IB2 Revision
1.
Topic 7
What changes occur when the temperature is increased in the following reaction at equilibrium?
Br2(g) + Cl2(g)
ο
2BrCl(g)
∆H = +14 kJ
–1
mol
Position of equilibrium
Shifts towards the reactants
Shifts towards the reactants
Shifts towards the products
Shifts towards the products
A.
B.
C.
D.
2.
Value of equilibrium constant
Decreases
Increases
Decreases
Increases
The sequence of diagrams represents the system as time passes for a gas phase reaction in which
reactant X is converted to product Y.
Diagram 1
t = 7 seconds
Diagram 2
t = 5 minutes
Diagram
t = 10 minutes
Diagram 4
t = 5 days
Time, t
X=
Y=
Which statement is correct?
A.
B.
C.
D.
3.
At t = 5 days the rate of the forward reaction is greater than the rate of the backward
reaction.
At t = 7 seconds the reaction has reached completion.
At t = 10 minutes the system has reached a state of equilibrium.
At t = 5 days the rate of the forward reaction is less than the rate of the backward
reaction.
The equation for the Haber process is:
Ө
N2(g) + 3H2(g)
2NH3(g) ∆H = −92.2 kJ
Which conditions will favour the production of the greatest amount of ammonia at equilibrium?
A.
B.
C.
D.
High temperature and high pressure
High temperature and low pressure
Low temperature and high pressure
Low temperature and low pressure
1
4.
Sulfur dioxide and oxygen react to form sulfur trioxide according to the equilibrium.
2SO2(g) + O2(g)
2SO3(g)
How is the amount of SO2 and the value of the equilibrium constant for the reaction affected by
an increase in pressure?
A.
B.
C.
D.
5.
The amount of SO3 and the value of the equilibrium constant both increase.
The amount of SO3 and the value of the equilibrium constant both decrease.
The amount of SO3 increases but the value of the equilibrium constant decreases.
The amount of SO3 increases but the value of the equilibrium constant does not change.
What is the equilibrium constant expression, Kc, for the reaction below?
N2(g) + 2O2(g)
A.
B.
6.
2NO2(g)
[NO 2 ]
Kc = [N ][O ]
2
2
2[NO 2 ]
Kc = 3[N ][O ]
2
2
C.
Kc =
D.
Kc =
[NO 2 ]2
[N 2 ][O 2 ]2
[NO 2 ]2
[N 2 ] + [O 2 ]2
Consider the following equilibrium reaction in a closed container at 350°C
SO2(g) + Cl2(g)
Ө
SO2Cl2(g) ∆H = −85 kJ
Which statement is correct?
A.
B.
C.
D.
7.
Decreasing the temperature will increase the amount of SO2Cl2(g).
Increasing the volume of the container will increase the amount of SO2Cl2(g).
Increasing the temperature will increase the amount of SO2Cl2(g).
Adding a catalyst will increase the amount of SO2Cl2(g).
Which of the following equilibria would not be affected by pressure changes at constant
temperature?
A.
B.
C.
D.
4HCl(g) + O2(g)
2H2O(g) + 2Cl2(g)
CO(g) + H2O(g)
H2(g) + CO2(g)
C2H5OH(g)
C2H4(g) + H2O(g)
PF3Cl2(g)
PF3(g) + Cl2(g)
2
8.
Consider the following equilibrium reaction in a closed container at 350°C.
SO2(g) + Cl2(g)
SO2Cl2(g)
Ө
∆H = −85 kJ
Which statement is correct?
A.
B.
C.
D.
9.
Decreasing the temperature will increase the amount of SO2Cl2(g).
Increasing the volume of the container will increase the amount of SO2Cl2(g).
Increasing the temperature will increase the amount of SO2Cl2(g).
Adding a catalyst will increase the amount of SO2Cl2(g).
Iron(III) ions react with thiocyanate ions as follows.
3+
–
Fe (aq) + CNS (aq)
2+
Fe(CNS) (aq)
What are the units of the equilibrium constant, Kc, for the reaction?
10.
–3
A.
mol dm
B.
mol dm
C.
mol dm
D.
mol dm
2
–6
–1
3
–2
6
Which changes cause an increase in the equilibrium yield of SO3(g) in this reaction?
2SO2(g) + O2(g)
I.
II.
III.
A.
B.
C.
D.
11.
Ө
2SO3(g) ∆H = –196 kJ
increasing the pressure
decreasing the temperature
adding oxygen
I and II only
I and III only
II and III only
I, II and III
The equation for a reaction used in the manufacture of nitric acid is
4NH3(g) + 5O2(g)
4NO(g) + 6H2O(g)
Ө
∆H = –900 kJ
Which changes occur when the temperature of the reaction is increased?
A.
B.
C.
D.
Position of equilibrium
Value of Kc
shifts to the left
shifts to the left
shifts to the right
shifts to the right
increases
decreases
increases
decreases
3
12. The equation for a reversible reaction used in industry to convert methane to hydrogen is shown
below.
CH4(g) + H2O(g)
Ө
CO(g) + 3H2(g)
∆H = +210 kJ
Which statement is always correct about this reaction when equilibrium has been reached?
13.
A.
B.
C.
The concentrations of methane and carbon monoxide are equal.
The rate of the forward reaction is greater than the rate of the reverse reaction.
The amount of hydrogen is three times the amount of methane.
D.
The value of ∆H for the reverse reaction is –210 kJ.
Which statement is always true for a chemical reaction that has reached equilibrium?
A.
B.
C.
D.
14.
Ө
The yield of product(s) is greater than 50%.
The rate of the forward reaction is greater than the rate of the reverse reaction.
The amounts of reactants and products do not change.
Both forward and reverse reactions have stopped.
Which changes will shift the position of equilibrium to the right in the following reaction?
2CO2(g)
I.
II.
III.
A.
B.
C.
D.
15.
adding a catalyst
decreasing the oxygen concentration
increasing the volume of the container
I and II only
I and III only
II and III only
I, II and III
A sealed container at room temperature is half full of water. The temperature of the container is
increased and left for equilibrium to re-establish. Which statement is correct when the
equilibrium is re-established at the higher temperature?
A.
B.
C.
D.
16.
2CO(g) +O2(g)
The rate of vaporization is greater than the rate of condensation.
The amount of water vapour is greater than the amount of liquid water.
The amount of water vapour is greater than it is at the lower temperature.
The rate of condensation is greater than the rate of vaporization.
The manufacture of sulfur trioxide can be represented by the equation below.
2SO2(g) + O2(g)
2SO3(g)
ο
∆H = –197 kJ mol
–1
What happens when a catalyst is added to an equilibrium mixture from this reaction?
A.
B.
The rate of the forward reaction increases and that of the reverse reaction decreases.
The rates of both forward and reverse reactions increase.
C.
D.
The value of ∆H increases.
The yield of sulfur trioxide increases.
ο
4
17.
Which statements are correct for a reaction at equilibrium?
I.
II.
III.
A.
B.
C.
D.
18.
I and II only
I and III only
II and III only
I, II and III
A liquid and its vapour are at equilibrium inside a sealed container. Which change will alter the
equilibrium vapour pressure of the liquid in the container?
A.
B.
C.
D.
19.
The forward and reverse reactions both continue.
The rates of the forward and reverse reactions are equal.
The concentrations of reactants and products are equal.
Adding more liquid
Adding more vapour
Decreasing the volume of the container
Decreasing the temperature
For the reaction below:
H2(g) + I2(g)
2HI(g)
–3
at a certain temperature, the equilibrium concentrations, in mol dm , are
[H2(g)] = 0.30, [I2(g)] = 0.30, [HI(g)] = 3.0
What is the value of K?
20.
–2
A.
B.
C.
1.0×10
10
33
D.
1.0×10
2
3
A 1.0 dm reaction vessel initially contains 6.0 mol of P and 6.0 mol of Q. At equilibrium 4.0
mol of R is present. What is the value of Kc for the following reaction?
P(g) + Q(g)
A.
B.
C.
D.
21.
R(g) + S(g)
0.11
0.25
0.44
4.00
The expression for the equilibrium constant for a reaction is
Kc =
[B][C]
[A ]2
–3
At a certain temperature the values of [A], [B] and [C] are all 0.2 mol dm . What happens to
–3
the value of Kc when all three values are doubled to 0.4 mol dm ?
A.
It is halved.
B.
It does not change.
C.
It doubles.
D.
It increases by a factor of four.
5
22.
Hydrogen and carbon dioxide react as shown in the equation below.
H2(g) + CO2(g)
H2O(g) + CO(g)
For this reaction the values of Kc with different temperatures are
Kc
Temperature / K
500
7.76×10
700
1.23×10
900
6.01×10
–3
–1
–1
Which statement for the reaction is correct?
A.
B.
C.
D.
23.
The forward reaction is endothermic.
H2O(g) and CO(g) are more stable than H2(g) and CO2(g).
The reaction goes almost to completion at high temperatures.
The reverse reaction is favoured by high temperatures.
The equation for the main reaction in the Haber process is:
N2(g) + 3H2(g)
(i)
2NH3(g)
∆H is negative
Determine the equilibrium constant expression for this reaction.
.........................................................................................................................................................
(1)
(ii)
State and explain the effect on the equilibrium yield of ammonia with increasing the
pressure and the temperature.
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
(4)
(iii)
In practice, typical conditions used in the Haber process involve a temperature of 500°C
and a pressure of 200 atm. Explain why these conditions are used rather than those that
give the highest yield.
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
(2)
6
(iv)
3
3
At a certain temperature and pressure, 1.1 dm of N2(g) reacts with 3.3 dm of H2(g).
Calculate the volume of NH3(g), that will be produced.
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
(1)
(v)
Suggest why this reaction is important for humanity.
.........................................................................................................................................................
.........................................................................................................................................................
(1)
(vi)
A chemist claims to have developed a new catalyst for the Haber process, which increases
the yield of ammonia. State the catalyst normally used for the Haber process, and
comment on the claim made by this chemist.
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
(2)
(Total 11 marks)
24.
The diagrams below represent equilibrium mixtures for the reaction Y + X2
XY + X at
350 K and 550 K respectively. Deduce and explain whether the reaction is exothermic or
endothermic.
X=
350 K
550 K
Y=
.........................................................................................................................................................
.........................................................................................................................................................
(Total 2 marks)
7
25.
In the gaseous state, methane and steam react to form hydrogen and carbon dioxide.
(i)
Write an equation for the endothermic equilibrium reaction. Deduce the equilibrium
expression for the reaction and state its units.
.........................................................................................................................................................
(4)
(ii)
Deduce and explain the conditions of temperature and pressure under which the forward
reaction is favoured.
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
(4)
(iii)
Explain, at the molecular level, why the reaction is carried out at high pressure in
industry.
.........................................................................................................................................................
.........................................................................................................................................................
(2)
(Total 10 marks)
26.
The equation for the exothermic reaction in the Contact process is given below:
2SO2(g) + O2(g)
(i)
2SO2(g)
Write the equilibrium constant expression for the reaction.
.........................................................................................................................................................
.........................................................................................................................................................
(1)
(ii)
State and explain qualitatively the pressure and temperature conditions that will give the
highest yield of sulfur trioxide.
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
(4)
(iii)
In practice, conditions used commercially in the Contact process are 450°C and 2
atmospheres of pressure. Explain why these conditions are used rather than those that
give the highest yield.
.........................................................................................................................................................
.........................................................................................................................................................
(3)
8
(iv)
Name a catalyst used in the Contact process. State and explain its effect on the value of
the equilibrium constant.
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
(3)
(Total 11 marks)
Consider the following reaction where colourless bromide ions react with colourless hydrogen
peroxide to form a red-brown bromine solution.
27.
–
+
2Br (aq) + H2O2(aq) + 2H (aq)
(a)
Br2(aq) + 2H2O(l)
∆H = negative
Predict and explain the effect on the position of equilibrium when
(i)
a small amount of sodium bromide solution is added.
.............................................................................................................................................
.............................................................................................................................................
(2)
(ii)
a small amount of sodium hydroxide solution is added.
.............................................................................................................................................
.............................................................................................................................................
(2)
(iii)
a catalyst is added.
.............................................................................................................................................
.............................................................................................................................................
(2)
(b)
State and explain the effect on the value of the equilibrium constant when the
temperature of the reaction is increased.
.........................................................................................................................................................
.........................................................................................................................................................
(2)
(c)
State and explain the colour change when hydrochloric acid is added to the reaction
solution at equilibrium.
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
(3)
(Total 11 marks)
9
28.
Ammonia is produced by the Haber process according to the following reaction.
N2(g) + 3H2(g)
(a)
2NH3(g) ∆H is negative
State the equilibrium constant expression for the above reaction.
....................................................................................................................................
....................................................................................................................................
(1)
(b)
Predict, giving a reason, the effect on the position of equilibrium when the pressure in the
reaction vessel is increased.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(c)
State and explain the effect on the value of Kc when the temperature is increased.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(d)
Explain why a catalyst has no effect on the position of equilibrium.
....................................................................................................................................
....................................................................................................................................
(1)
(Total 6 marks)
29.
The equation for a reaction used in industry is
CH4(g) + H2O(g)
3H2(g) + CO(g)
Ө
∆H = +210 kJ
Deduce the equilibrium constant expression, Kc, for this reaction.
....................................................................................................................................
(Total 1 mark)
10
30.
Many reversible reactions in industry use a catalyst. State and explain the effect of a catalyst on
the position of equilibrium and on the value of Kc.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(Total 4 marks)
31.
Consider the following reaction in the Contact process for the production of sulfuric acid for
parts (a) to (c) in this question.
2SO3
2SO2 + O2
(a)
Write the equilibrium constant expression for the reaction.
....................................................................................................................................
(1)
(b)
(i)
State the catalyst used in this reaction of the Contact process.
....................................................................................................................................
(1)
(ii)
State and explain the effect of the catalyst on the value of the equilibrium constant
and on the rate of the reaction.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(4)
(c)
Using Le Chatelier’s principle explain the effect on the position of equilibrium of
(i)
increasing the pressure at constant temperature.
....................................................................................................................................
....................................................................................................................................
(2)
(ii)
removing sulfur trioxide.
....................................................................................................................................
....................................................................................................................................
(2)
(Total 10 marks)
11
32.
Consider the following reaction in the Contact process for the production of sulfuric acid for
parts (a) to (d) in this question.
2SO2 + O2
2SO3
(a)
Write the equilibrium constant expression for the reaction.
....................................................................................................................................
(1)
(b)
(i)
State the catalyst used in this reaction of the Contact process.
....................................................................................................................................
(1)
(ii)
State and explain the effect of the catalyst on the value of the equilibrium constant
and on the rate of the reaction.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(4)
(c)
Use the collision theory to explain why increasing the temperature increases the rate of
the reaction between sulfur dioxide and oxygen.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(d)
Using Le Chatelier’s principle state and explain the effect on the position of equilibrium
of
(i)
increasing the pressure at constant temperature.
....................................................................................................................................
....................................................................................................................................
(2)
(ii)
removing of sulfur trioxide.
....................................................................................................................................
....................................................................................................................................
(2)
(iii)
using a catalyst.
....................................................................................................................................
....................................................................................................................................
(2)
(Total 14 marks)
12
33.
The equation for one reversible reaction involving oxides of nitrogen is shown below:
N2O4(g)
Ө
2NO2(g)
∆H = +58 kJ
Experimental data for this reaction can be represented on the following graph:
1.0
product
0.8
concentration
/ mol dm –3
0.6
reactant
0.4
0.2
0
(i)
2
4
6
Time / min
8
10
Write an expression for the equilibrium constant, Kc, for the reaction. Explain the
significance of the horizontal parts of the lines on the graph. State what can be deduced
about the magnitude of Kc for the reaction, giving a reason.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(4)
(ii)
Use Le Chatelier’s principle to predict and explain the effect of increasing the
temperature on the position of equilibrium.
....................................................................................................................................
....................................................................................................................................
(2)
(iii)
Use Le Chatelier’s principle to predict and explain the effect of increasing the pressure on
the position of equilibrium.
....................................................................................................................................
....................................................................................................................................
(2)
(iv)
State and explain the effects of a catalyst on the forward and reverse reactions, on the
position of equilibrium and on the value of Kc.
....................................................................................................................................
....................................................................................................................................
(6)
(Total 14 marks)
13
34.
The equation for another reaction used in industry is
CO(g) + H2O(g)
(i)
H2(g) + CO2(g)
Ө
∆H = −42 kJ
Under certain conditions of temperature and pressure, 2.0 mol of carbon monoxide and
3.2 mol of steam were left to reach equilibrium. At equilibrium, 1.6 mol of both hydrogen
and carbon dioxide were present.
Calculate the amounts of carbon monoxide and steam at equilibrium and the value of Kc.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
(ii)
Under the same conditions of temperature and pressure, 2.0 mol of carbon monoxide and
2.0 mol of steam were left to reach equilibrium.
Calculate the amounts of each reactant and product at equilibrium.
(If you were unable to calculate a value for Kc in (i) use the value 9.0, although this is not
the correct value.)
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 5 marks)
35.
(a)
The equation for the decomposition of hydrogen iodide is
Ө
2HI(g)
H2(g) + I2(g)∆H = +52 kJ
Predict and explain the effect on the position of equilibrium of
(i)
increasing the pressure, at constant temperature.
....................................................................................................................................
....................................................................................................................................
(2)
(ii)
increasing the temperature, at constant pressure.
....................................................................................................................................
....................................................................................................................................
(2)
14
15
(iii)
adding a catalyst, at constant temperature and pressure.
....................................................................................................................................
....................................................................................................................................
(2)
(b)
Deduce the expression for Kc for the forward reaction.
....................................................................................................................................
....................................................................................................................................
(1)
(c)
The equilibrium formed during this reaction was investigated in two experiments carried
out at different temperatures. The results are shown in the table below.
Experiment
number
1
2
(i)
Initial concentration / mol
–3
[HI]
0.06
0.00
dm
[H2]
0.00
0.04
Equilibrium concentration
–3
[I2]
0.00
0.04
/ mol dm
[H2]
[HI]
0.01
0.04
[I2]
For each experiment, deduce the concentrations of the other species present at
equilibrium. Calculate the values of Kc for the forward reaction for each
experiment.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(6)
(ii)
Use the two calculated values of Kc to deduce which of the two experiments was
carried out at the higher temperature, and explain your choice. (If you were not
able to calculate the values of Kc in (c)(i), assume that the values are 0.1 for
experiment 1 and 0.2 for experiment 2, although these are not the correct values.)
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 15 marks)
16
IB2 Revision
36.
Which methods will distinguish between equimolar solutions of a strong base and a strong acid?
I.
II.
Add magnesium to each solution and look for the formation of gas bubbles.
Add aqueous sodium hydroxide to each solution and measure the temperature
change.
Use each solution in a circuit with a battery and lamp and see how bright the lamp
glows.
III.
A.
B.
C.
D.
37.
I and II only
I and III only
II and III only
I, II and III
–3
Which substance, when dissolved in water, to give a 0.1 mol dm solution, has the highest pH?
A.
B.
C.
D.
38.
Topic 8
HCl
NaCl
NH3
NaOH
Which species can act as a Lewis acid?
A.
BF3
B.
C.
D.
OH
H2O
NH3
–
–
39.
What is the conjugate base of the HSO4 (aq) ion?
A.
H2SO4(aq)
B.
C.
SO4 (aq)
H2O(l)
D.
H3O (aq)
2–
40.
+
The pH of a solution changes from pH = 1 to pH = 3. What happens to the [H ] during this pH
change?
A.
B.
C.
D.
41.
+
It increases by a factor of 100.
It decreases by a factor of 100.
It increases by a factor of 1000.
It decreases by a factor of 1000.
Which acids are strong?
I.
II.
III.
A.
B.
C.
HCl(aq)
HNO3(aq)
H2SO4(aq)
I and II only
I and III only
II and III only
17
D.
42.
Solutions of hydrochloric acid (HCl(aq)) and ethanoic acid (CH3COOH(aq)) of the same
concentration reacted completely with 5.0 g of calcium carbonate in separate containers. Which
statement is correct?
A.
B.
C.
D.
43.
CH3COOH(aq) reacted slower because it has a lower pH than HCl(aq).
A smaller volume of CO2(g) was produced with CH3COOH(aq) than with HCl(aq).
A greater volume of CO2(g) was produced with CH3COOH(aq) than with HCl(aq).
The same volume of CO2(g) was produced with both CH3COOH(aq) and HCl(aq).
Solutions of hydrochloric acid (HCl(aq)) and ethanoic acid (CH3COOH(aq)) of the same
concentration reacted completely with 5.0 g of calcium carbonate in separate containers. Which
statement is correct?
A.
B.
C.
D.
44.
I, II and III
CH3COOH(aq) reacted slower because it has a lower pH than HCl(aq).
A smaller volume of CO2(g) was produced with CH3COOH(aq) than with HCl(aq).
A greater volume of CO2(g) was produced with CH3COOH(aq) than with HCl(aq).
The same volume of CO2(g) was produced with both CH3COOH(aq) and HCl(aq).
Which is a Brønsted-Lowry acid-base pair?
2–
A.
H2O and O
B.
CH3COOH and CH3COO
C.
NH4 and NH2
D.
H2SO4 and SO4
–
+
–
2–
45.
Lime is added to a lake to neutralize the effects of acid rain. The pH value of the lake water
+
rises from 4 to 7. What is the change in concentration of H ions in the lake water?
A.
B.
C.
D.
46.
Which is not a strong acid?
A.
B.
C.
D.
47.
An increase by a factor of 3
An increase by a factor of 1000
A decrease by a factor of 3
A decrease by a factor of 1000
Nitric acid
Sulfuric acid
Carbonic acid
Hydrochloric acid
Which species are a conjugate pair according to the Brønsted-Lowry theory?
A.
B.
CH3COOH and CH3CHO
NH3 and BF3
C.
H2NO3 and NO3
D.
H2SO4 and HSO4
+
–
–
18
19
48.
Which methods can distinguish between solutions of a strong monoprotic acid and a weak
monoprotic acid of the same concentration?
I.
Add magnesium to each solution and measure the rate of the formation of gas
bubbles.
Add aqueous sodium hydroxide to each solution and measure the temperature
change.
Use each solution in a circuit with a battery and lamp and see how bright the lamp
glows.
II.
III.
A.
B.
C.
D.
49.
50.
+
Which change in [H ] causes the biggest increase in pH?
52.
–3
–2
–3
+
–3
–4
–3
+
–4
–2
–3
+
–4
–6
–3
A change in [H (aq)] from 1×10 to 1×10 mol dm
B.
A change in [H (aq)] from 1×10 to 1×10 mol dm
C.
A change in [H (aq)] from 1×10 to 1×10 mol dm
D.
A change in [H (aq)] from 1×10 to 1×10 mol dm
Which statement about indicators is always correct?
The mid-point of the pH range of an indicator is 7.
The pH range is greater for indicators with higher pKa values.
The colour red indicates an acidic solution.
The pKa value of the indicator is within its pH range.
–2
At 25°C, Ka for an acid is 1.0×10 . What is the value of Kb for its conjugate base?
2
A.
1.0×10
B.
1.0×10
C.
1.0×10
D.
1.0×10
–2
12
–12
–3
Which values are correct for a 0.010 mol dm solution of NaOH(aq) at 298 K?
–14
(Kw = 1.0×10
53.
+
A.
A.
B.
C.
D.
51.
I and II only
I and III only
II and III only
I, II and III
2
–6
mol dm at 298 K)
+
–12
A.
[H ] = 1.0×10
B.
[OH ] = 1.0×10
C.
[H ] = 1.0×10
D.
[OH ] = 1.0×10
–
+
–
–3
mol dm and pH = 12.00
–12
–12
–3
mol dm and pH = 12.00
–3
mol dm and pOH = 12.00
–12
–3
mol dm and pOH = 12.00
An acid-base indicator has a pKa value of 4.0. At what pH will this indicator change colour?
A.
B.
C.
2.0
4.0
8.0
20
D.
54.
Which salt forms the most acidic solution when added to water?
A.
B.
C.
D.
55.
12.0
NaCl
MgSO4
Al(NO3)3
KHCO3
+
–3
What is the value of [H ] in a buffer solution in which [CH3COOH] = 2.0 mol dm and
–
–3
–5
–3
[CH3COO ] 1.0 mol dm ? For CH3COOH, Ka = 1.8×10 mol dm .
56.
–3
A.
6.0×10
B.
3.6×10
C.
1.8×10
D.
9.1×10
–5
–5
–6
–3
3
A base of concentration 0.10 mol dm is titrated with 25 cm of an acid of concentration 0.10
–3
mol dm . Which base-acid pair would have the highest pH at the equivalence point?
A.
B.
C.
D.
57.
3
–3
3
10 cm of 0.01 mol dm nitric acid (HNO3) is diluted with 90 cm of water. What is the pH of
the resulting solution?
A.
B.
C.
D.
58.
NaOH(aq) and CH3COOH(aq)
NaOH(aq) and HNO3(aq)
NH3(aq) and HNO3(aq)
NH3(aq) and CH3COOH(aq)
1
2
3
4
The pKa values of four acids are as follows.
W
X
Y
Z
4.87
4.82
4.86
4.85
What is the correct order when these acids are arranged in order of increasing acid strength?
A.
B.
C.
D.
X, Z, Y, W
X, Y, Z, W
W, Z, Y, X
W, Y, Z, X
21
59.
Ammonia (NH3) is a weak base in aqueous solution with an ionization constant Kb. What
expression is equal to the ionization constant for the following reaction?
+
NH4 (aq) + H2O(l)
A.
B.
C.
D.
60.
Kw
Ka
Ka
Kw
Kw
Kb
Kb
Kw
3
Which mixture would produce a buffer solution when dissolved in 1.0 dm of water?
A.
B.
C.
D.
61.
+
NH3(aq) + H3O (aq)
0.30 mol of NH3(aq) and 0.30 mol of HCl(aq)
0.30 mol of NH3(aq) and 0.15 mol of HCl(aq)
0.30 mol of NH3(aq) and 0.60 mol of HCl(aq)
0.30 mol of NH3(aq) and 0.15 mol of H2SO4(aq)
Water dissociates according to the equation
H2O(l)
+
–
H (aq) + OH (aq)
∆H = +56 kJ
At 25°C water has a pH of 7. Which of the following occurs when water is heated to 30°C?
A.
B.
C.
D.
62.
Which neutralization reaction could use phenolphthalein (pKa = 9.3) and not methyl orange
(pKa = 3.7) as an indicator?
A.
B.
C.
D.
63.
It remains neutral and its pH decreases.
It becomes acidic and its pH decreases.
It remains neutral and its pH increases.
It becomes acidic and its pH increases.
NaOH(aq) and HNO3(aq)
NH3(aq) and CH3COOH(aq)
NaOH(aq) and CH3COOH(aq)
NH3(aq) and HNO3(aq)
Which solution has the lowest pH value?
A.
B.
C.
D.
Aluminium sulfate
Sodium nitrate
Potassium chloride
Sodium ethanoate
22
64.
–3
Which salt, when dissolved in water to form a 1.0 mol dm solution, produces the lowest pH
value?
A.
B.
C.
D.
65.
66.
67.
Ammonium chloride
Ammonium ethanoate
Sodium ethanoate
Sodium chloride
Which is the correct statement about the pH and pOH values of an aqueous solution at 25°C?
A.
pH + pOH =14.0
B.
C.
pH + pOH =1.0 ×10
pH × pOH =14.0
D.
pH × pOH =1.0 ×10
–14
–14
The strengths of organic acids can be compared using Ka and pKa values. Which acid is the
strongest?
A.
B.
C.
Acid A
Acid B
Acid C
pKa = 6
pKa = 3
D.
Acid D
Ka = 1×10
–5
Ka = 1×10
–4
When the following acids are listed in decreasing order of acid strength (strongest first), what is
the correct order?
Ka
–5
benzoic
6.31×10
A.
B.
C.
D.
–3
chloroethanoic
1.38×10
ethanoic
1.74×10
–5
chloroethanoic > benzoic > ethanoic
benzoic > ethanoic > chloroethanoic
chloroethanoic > ethanoic > benzoic
ethanoic > benzoic > chloroethanoic
23
68.
Which graph shows how the pH changes when a weak base is added to a strong acid?
pH
pH
14
14
A
B
7
7
0
0
volume of base
volume of base
pH
14
pH
14
C
D
7
7
0
0
volume of base
69.
An aqueous solution has a pH of 10. Which concentrations are correct for the ions below?
+
[H (aq)] mol dm
70.
volume of base
A.
10
B.
10
C.
10
D.
10
4
–4
–10
–10
–3
–
[OH (aq)] mol dm
10
10
–3
–10
–10
10
10
–4
–4
Which compound will dissolve in water to give a solution with a pH greater than 7?
A.
B.
C.
D.
sodium chloride
potassium carbonate
ammonium nitrate
lithium sulfate
24
71.
The pKb values of some amines are shown in Table 15 of the Data Booklet. Write an equation
for the reaction of ethylamine with water. State and explain how the basicity of ethylamine
compares to that of ammonia.
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
(Total 4 marks)
(a) (i)
A solution of hydrochloric acid has a concentration of 0.10 mol dm
and a pH value of 1. The solution is diluted by a factor of 100. Determine the
concentration of the acid and the pH value in the diluted solution.
..........................................................................................................................
72.
–3
..........................................................................................................................
..........................................................................................................................
(2)
(ii)
–3
Explain why 0.10 mol dm ethanoic acid solution and the diluted solution in (a) (i)
+
have similar [H ] values.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(3)
(b)
Suggest one method, other than measuring pH, which could be used to distinguish
between solutions of a strong acid and a weak acid of the same concentration. State the
expected results.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 7 marks)
25
73.
State an equation for the reaction of propanoic acid with water. Identify one conjugate
Brønsted-Lowry pair.
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
(Total 2 marks)
74.
Propanoic acid is classified as a weak acid.
(a) State the meaning of the term weak acid.
....................................................................................................................................
....................................................................................................................................
(1)
(b)
State, giving a reason in each case, two methods other than measuring pH, that could be
–3
–3
used to distinguish between 0.100 mol dm propanoic acid and 0.100 mol dm nitric
acid.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 3 marks)
75.
State and explain two methods, other than measuring pH, which could be used to distinguish
–3
between 1.0 mol dm solutions of nitric acid and ethanoic acid.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(Total 4 marks)
26
76.
The pH values of three acidic solutions, X, Y and Z, are shown in the following table:
Solution
X
Y
Z
(i)
Acid
HCl(aq)
HCl(aq)
CH3COOH(aq)
pH
2
4
4
Solutions X and Z have the same acid concentration. Explain, by reference to both acids,
why they have different pH values.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(ii)
+
Deduce by what factor the values of [H ] in solutions X and Y differ.
....................................................................................................................................
....................................................................................................................................
(1)
(Total 3 marks)
77.
Define the terms Brønsted-Lowry acid and Lewis acid. For each type of acid, identify one
example other than water and write an equation to illustrate the definition.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(Total 5 marks)
78.
Vinegar has a pH of approximately 3 and some detergents have a pH of approximately 8. State
+
and explain which of these has the higher concentration of H and by what factor.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(Total 1 mark)
27
79.
Identify one example of a strong acid and one example of a weak acid. Outline three different
methods to distinguish between equimolar solutions of these acids in the laboratory. State how
the results would differ for each acid.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(Total 5 marks)
80.
The equilibrium reached when ethanoic acid is added to water can be represented by the
following equation:
–
CH3COOH(l) + H2O(l)
+
CH3COO (aq)+H3O (aq)
Define the terms Brønsted-Lowry acid and Lewis base, and identify two examples of each of
these species in the equation.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(Total 4 marks)
81.
(a)
The dissociation of water takes place as follows:
(i)
H2O(l)
H (aq) + OH (aq)
State the expression for the ionic product constant of water, Kw.
+
–
.........................................................................................................................
.........................................................................................................................
(1)
(ii)
The value of Kw is 2.4×10
–14
2
–6
+
mol dm at 310 K. Calculate the [H ] at 310 K.
.........................................................................................................................
.........................................................................................................................
(1)
28
(b)
Lactic acid CH3CH(OH)COOH is a weak monoprotic acid
–4
–3
(pKa = 3.85 and Ka = 1.4×10 mol dm ).
(i)
Write an equation for the reaction of lactic acid with water.
.........................................................................................................................
.........................................................................................................................
(1)
(ii)
State the ionization constant expression, Ka, for lactic acid.
.........................................................................................................................
.........................................................................................................................
(1)
(iii)
–3
Calculate the pH of a 0.20 mol dm solution of lactic acid.
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
(2)
(iv)
–3
Determine the pH of a solution containing 0.10 mol dm of lactic acid and 0.10
–3
mol dm of sodium lactate.
.........................................................................................................................
.........................................................................................................................
(1)
(Total 7 marks)
82.
The pH of a solution is 4.8. Using information from Table 17 of the Data Booklet, deduce and
explain the colours of the indicators bromophenol blue and phenol red in this solution.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(Total 3 marks)
83.
–3
Calculate the pH of a buffer solution containing 0.0500 mol dm of ethanoic acid
–5
–3
(Ka = 1.74×10 ) and 0.100 mol of sodium ethanoate.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(Total 3 marks)
29
84.
Describe the composition and behaviour of a buffer solution.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(Total 3 marks)
(a)
85.
(i)
Write the equation for the reaction of ammonia with water.
.........................................................................................................................
.........................................................................................................................
(1)
(ii)
Derive the expression for Kb for this reaction.
.........................................................................................................................
.........................................................................................................................
(1)
(b)
Using information from Table 16 in the Data Booklet, determine the pOH of a
–3
0.20 mol dm solution of ammonia.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
(Total 5 marks)
86.
(i)
Define the term pH.
....................................................................................................................................
....................................................................................................................................
(1)
30
(ii)
3
–3
A 25.0 cm sample of 0.100 mol dm hydrochloric acid was placed in a conical flask,
–3
3
and 0.100 mol dm sodium hydroxide is added until a total of 50.0 cm had been added.
Sketch a graph of pH against volume of NaOH(aq) added, clearly showing the volume of
NaOH(aq) needed for complete reaction and the pH values at the start, the equivalence
point and finish.
(4)
(iii)
3
–3
The experiment in (ii) was repeated, but with a 25.0 cm sample of 0.100 mol dm
ethanoic acid in the conical flask instead of the hydrochloric acid. Use information from
Table 16 of the Data Booklet to calculate the pH at the start of the experiment. State the
approximate pH value at the equivalence point.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(5)
(Total 10 marks)
(i)
87.
Describe how an indicator, HIn, works.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
(ii)
Name a suitable indicator for the reaction between ethanoic acid and sodium hydroxide.
Use information from Table 17 in the Data Booklet to explain your choice.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 5 marks)
31
(i)
88.
Identify two substances that can be added to water to form a basic buffer solution.
....................................................................................................................................
....................................................................................................................................
(1)
(ii)
Describe what happens when a small amount of acid solution is added to the buffer
solution prepared in (i). Use an equation to support your explanation.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 3 marks)
89.
–3
Predict and explain whether an aqueous solution of 0.10 mol dm AlCl3 will be acidic, alkaline
or neutral.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(Total 2 marks)
90.
3
A titration was carried out to determine the concentration of 25.0 cm of an aqueous solution of
–3
nitric acid. The pH value of the liquid in the flask was measured as 0.100 mol dm , aqueous
sodium hydroxide was added. The results are shown on the graph below.
14
12
10
pH
8
6
4
2
0
(i)
30
20
10
Volume of NaOH(aq) / cm 3
40
+
Use the graph to determine the value of [H ] of the nitric acid solution.
....................................................................................................................................
....................................................................................................................................
(1)
32
(ii)
+
–3
–3
Determine the pH value when the value of [H ] has decreased to 1×10 mol dm .
....................................................................................................................................
....................................................................................................................................
(1)
(iii)
–3
Use the graph to determine the volume of 0.100 mol dm aqueous sodium hydroxide
solution needed to exactly neutralize the nitric acid.
....................................................................................................................................
....................................................................................................................................
(1)
(iv)
–3
Calculate the concentration, in mol dm , of the nitric acid.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 5 marks)
91.
In aqueous solution at 298 K, ammonia is a weak base with a pKb value of 4.75 and a Kb value
–5
–3
of 1.7×10 mol dm .
(a) Write an equation for the reaction of ammonia with water.
....................................................................................................................................
....................................................................................................................................
(1)
(b)
State the ionization constant expression, Kb, for ammonia.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(1)
(c)
–3
Calculate the pH of a 0.25 mol dm solution of ammonia.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
(Total 5 marks)
33
(a)
92.
–3
Explain why a 1.0 mol dm solution of sodium hydroxide has a pH of 14 whereas
–3
1.0 mol dm ammonia solution has a pH of about 12. Use equations in your answer.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(5)
(b)
3
20.0 cm of a known concentration of sodium hydroxide is titrated with a solution of
nitric acid. The graph for this titration is given below.
13
pH
7
0
(i)
10
20
Volume of nitric acid / cm 3
30
State an equation for the reaction between sodium hydroxide and nitric acid.
....................................................................................................................................
....................................................................................................................................
(1)
(ii)
Calculate the concentration of the sodium hydroxide solution before the titration.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(iii)
From the graph determine the volume of nitric acid required to neutralize the
sodium hydroxide and calculate the concentration of the nitric acid.
....................................................................................................................................
....................................................................................................................................
(2)
34
35
(iv)
Predict the volume of ethanoic acid of the same concentration as the nitric acid in
3
(b) (iii), required to neutralize 20.0 cm of this sodium hydroxide solution.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(1)
(Total 11 marks)
93.
Nitric acid and ammonia may be used to make a buffer solution.
(i)
Describe the behaviour of a buffer solution.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(ii)
–3
Describe how you could prepare a buffer solution using 0.100 mol dm solutions of
nitric acid and ammonia.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
(Total 5 marks)
94.
Benzoic acid, C6H5COOH, is a weak acid.
(a) Deduce the equation for the ionization of benzoic acid in water.
....................................................................................................................................
....................................................................................................................................
(1)
(b)
Use information from Table 16 in the Data Booklet to calculate a value for the
dissociation constant, Ka, for benzoic acid.
....................................................................................................................................
....................................................................................................................................
(1)
36
(c)
Derive the ionization constant expression for benzoic acid and use it to determine the pH
–3
of a 0.20 mol dm aqueous solution of benzoic acid.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
(Total 5 marks)
95.
–3
With reference to Table 16 in the Data Booklet, determine the pH of a 0.100 mol dm solution
of propanoic acid.
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
(Total 3 marks)
96.
The hydrogen ion concentration in pure water varies with temperature. At a particular
+
–7
–3
temperature [H ] =1.7×10 mol dm .
(a) State the expression for the ionic product constant of water, Kw, and calculate the value
of Kw at this temperature.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(b)
Calculate the pH of water at this temperature.
....................................................................................................................................
....................................................................................................................................
(1)
37
(c)
State and explain whether water at this temperature is acidic, neutral or alkaline.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 5 marks)
97.
–3
3
–3
0.100 mol dm hydrochloric acid solution is added to 25.0 cm 0.100 mol dm ammonia
3
solution and the pH is recorded until a total of 35.0 cm hydrochloric acid has been added.
(i)
Sketch a graph to show how the pH changes as hydrochloric acid is added to the
3
ammonia solution. Use a pH scale of 0–14, and an acid volume scale of 0–35 cm .
Explain the shape of the curve.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(6)
(ii)
Use table 17 of the Data Booklet to suggest an indicator that could be used in the
titration, explaining your choice.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 8 marks)
98.
(i)
State the composition of an acidic buffer solution.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(1)
38
(ii)
Suggest the identity of an acid and its amount that could be added to a solution
containing 0.10 mol ammonia in order to prepare a buffer.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(iii)
Explain how the solution you prepare in (ii) can act as a buffer solution when a strong
acid and a strong base are added to separate portions of it. Write an equation to
illustrate the buffer action in each case.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(4)
(iv)
Write an equation for the reaction of ammonia with water, and write its Kb expression.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(2)
(Total 9 marks)
99.
(a) Predict and explain, using equations where appropriate, whether the following
solutions are acidic, alkaline or neutral.
(i)
–3
0.1 mol dm FeCl3(aq)
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
–3
0.1 mol dm NaNO3(aq)
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
39
(1)
(iii)
–3
0.1 mol dm Na2CO3(aq)
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(1)
(b)
Acidic gases can be released into the atmosphere that have an environmental impact
when they are deposited as acid rain. State two elements that form the acidic gases and
describe two impacts they have on the natural environment.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(Total 6 marks)
100. An experiment was carried out to determine the concentration of aqueous ammonia by titrating
–3
3
it with a 0.150 mol dm sulfuric acid solution. It was found that 25.0 cm of the aqueous
3
ammonia required 20.1 cm of the sulfuric acid solution for neutralization.
(a)
–3
Write the equation for the reaction and calculate the concentration, in mol dm , of the
aqueous ammonia.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(4)
(b)
Several acid-base indicators are listed in Table 16 of the Data Booklet. Identify one
indicator that could be used for this experiment. Explain your answer.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(3)
40
(c)
(i)
4.75).
–3
Determine the pOH of 0.121 mol dm aqueous ammonia (pKb =
....................................................................................................................................
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(4)
(ii)
State what is meant by the term buffer solution, and describe the composition of an
acid buffer solution in general terms.
....................................................................................................................................
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(3)
(iii)
3
–3
Calculate the pH of a mixture of 50.0 cm of 0.100 mol dm aqueous ammonia
3
–3
and 50.0 cm of 0.0500 mol dm hydrochloric acid solution.
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(4)
(Total 18 marks)
41
1.
2.
3.
4.
5.
6.
7.
8.
D
C
C
D
C
A
B
A
9.
10.
11.
12.
13.
14.
15.
16.
C
D
B
D
C
C
C
B
A
D
D
D
B
A
17.
18.
19.
20.
21.
22.
[NH 3 ] 2
23.
[N 2 ][H 2 ]3
(i)
(Kc =)
(ignore units);
1
(ii)
Increasing the pressure:
Yield increases/equilibrium moves to the right/more ammonia;
4 gas molecules → 2/decrease in volume/fewer gas molecules
on right hand side;
Increasing the temperature:
Yield decreases/equilibrium moves to the left/less ammonia;
Exothermic reaction/OWTTE;
4
(iii)
(iv)
Higher temperature increases rate;
Lower pressure is less expensive/lower cost of operating at low
pressure/reinforced pipes not needed;
Do not award a mark just for the word “compromise”.
2
3
2.2 (dm );
1
Penalize incorrect units.
(v)
(vi)
Fertilizers/increasing crop yields;
Production of explosives for mining;
1 max
Fe/iron;
Allow magnetite/iron oxide.
Claim is not valid since catalysts do not alter the yield/position
of equilibrium/only increase the rate of reaction;
2
[11]
24.
less product is present at higher temperatures;
Therefore the forward reaction is exothermic;
2
[2]
25.
(i)
CH4(g) + 2H2O(g)
4H2(g) + CO2(g);
States not required. Award [1] for balanced equation and [1] for equilibrium sign.
[H 2 ] 4 [CO 2 ]
Kc =
[CH 4 ][H 2 O] 2
;
ECF
2
−6
2 −2
2 −2
2
units: mol dm /mol L /mol l ; do not accept: M
ECF
(ii)
(iii)
4
(endothermic reaction) increase in temperature (favours the forward
reaction);
absorbs (some of) the heat supplied/OWTTE;
Award no marks for saying: “because of Le Chatelier’s principle”.
low pressure (will allow system to occupy more volume);
Vproduct > Vreactant/reaction proceeds to greater number of gaseous moles
/molecules/more moles of gases on right/OWTTE;
ECF from (i)
4
at high pressure concentration increases/reaction rate faster;
more frequent collisions;
2
[10]
26.
(i)
(ii)
KC =
[SO 3 ] 2
[SO 2 ] 2 [O 2 ]
;
1
pressure
high pressure (will allow system to occupy smaller volume);
Vproduct <Vreactant/equilibrium moves to the right to reduce pressure
/reaction proceeds to lower/lowest number of gaseous molecules
/OWTTE;
Temperature
42
(iii)
(iv)
low temperature;
(exothermic reaction) forward reaction favoured to replace some
of the heat removed/equilibrium moves to the right to produce heat
/OWTTE;
No mark for just saying “due to Le Chatelier's principle”
rate is faster at 450°C (than at low temperatures);
>95%/90 − 99% yield/(very) high conversion takes place;
unnecessary to use expensive high pressure equipment/(to achieve) high
pressure is very expensive;
vanadium pentoxide/vanadium(V) oxide/V2O5/finely divided
platinum/Pt;
no effect on Kc;
forward and reverse rates speeded up (equally);
4
3
3
[11]
27.
(a)
(i)
(ii)
(iii)
(b)
(c)
shifts to the right/toward products/forward reaction favoured;
−
to consume excess Br added;
Do not accept “due to Le Chatelier’s principle”.
shifts to the left/toward reactants/reverse reaction favoured;
+
NaOH reacts to consume H /an increase in the amount of H2O
resulting from neutralization;
Do not accept “due to Le Chatelier’s principle”.
no effect;
catalyst increases the rate of the forward and backward reactions
equally/lowers the activation energy of both forward and backward
reaction equally/lowers EA so rate of forward and backward reactions
increase equally;
equilibrium constant decreases;
forward reaction is exothermic/produces heat/reverse reaction is endothermic
/absorbs heat;
colour change from red-brown to darker red-brown of Br2/red-brown colour
intensifies/OWTTE;
equilibrium position shifts to the right/products;
+
to consume H ;
2
2
2
2
3
[11]
28.
(a)
(k c ) =
[NH 3 ] 2
[H 2 ]3 [ N 2 ]
;
1
Do not allow round brackets unless Kp is used.
(b)
(c)
(d)
equilibrium shifts to the right/products;
4 mol → 2 mol of gas/fewer moles of gas on the right/products;
2
Kc decreases;
equilibrium position shifts to the left/reactants/forward reaction is exothermic
/reverse reaction is endothermic;
2
catalyst increases the rate of the forward and backward reactions equally
/lowers the activation energy of both forward and backward reaction equally
/lowers Ea so rate of forward and backward reactions increase;
1
[6]
29.
kc =
[H 2 ]3 [CO]
;
[CH 4 ][H 2 O]
[1]
30.
no effect on position of equilibrium;
forward and reverse reactions speeded up equally/affects the rate of reaction
but not the extent of the reaction;
no effect on value of Kc;
no change in concentrations of reactants or products/Kc only changes if
temperature alters;
[4]
31.
(a)
(b)
2
2
K / Kc = [SO3] ÷[SO2] [O2];
Exactly as written.
Accept correct Kp expression.
(i)
vanadium(V) oxide/(di)vanadium pentaoxide/V2O5/Pt;
Allow just vanadium oxide but not incorrect formula.
1
1
43
(ii)
(c)
(i)
(ii)
catalyst does not affect the value of Kc;
forward and reverse rate increase equally/by the same factor;
catalyst increases the rate of the reaction;
(by providing an alternative path for the reaction with) lower
activation energy;
shifts equilibrium position to the products/right;
to the side with least gas molecules or moles/lower volume of gas;
shifts equilibrium position to the products/right;
to compensate for loss of SO3/produce more SO3;
4
2
2
[10]
32.
(a)
2
2
K/Kc = [SO3] ÷[SO2] [O2];
Accept correct Kp expression.
1
(b)
(i)
1
(ii)
(c)
(d)
vanadium(V) oxide/(di)vanadium pentaoxide/V2O5;
Allow just vanadium oxide but not correct formula.
catalyst does not affect the value of Kc;
forward and reverse rates increase equally/by the same factor;
catalyst increases the rate of the reaction;
(by providing an alternative path for the reaction with) lower
activation energy;
more energetic collisions/more molecules have energy greater than
activation energy;
more frequent collisions;
Do not accept more collisions without reference to time.
(i)
(ii)
(iii)
shifts equilibrium position to the products/right;
to the side with fewer gas molecules or moles/lower volume of gas;
shifts equilibrium position to the products/right;
to compensate for loss of SO3/produce more SO3;
no effect;
forward and backward rates increased equally/by the same factor;
4
2
2
2
2
[14]
33.
(i)
(ii)
(iii)
(iv)
[NO 2 ] 2
( K c =)
;
[N 2 O 4 ]
(horizontal line) concentration of reactant and product remains constant/equilibrium reached;
(magnitude of) Kc greater than 1;
Accept 1.6.
product concentration greater than reactant concentration;
increased temperature shifts equilibrium position to right;
(forward) reaction is endothermic/absorbs heat;
increased pressure shifts equilibrium to left;
fewer (gas) moles/molecules on left;
both/forward and reverse rates increased/increase in forward reverse
rates are equal;
activation energy reduced;
position of equilibrium unchanged;
concentration/amount of reactants and products remain constant;
value of Kc unchanged;
Kc only affected by changes in temperature;
6
4
2
2
14]
34.
(i)
(ii)
CO = 0.4 (mol);
H2O = 1.6 (mol);
2
Kc (= 1.6 ÷0.4×1.6) = 4.0/4;
Apply ECF from Kc expression.
Ignore units.
H2 and CO2/products = 1.33/1.3 (mol);
CO and H2O/reactants = 0.67/0.7 (mol);
Using Kc = 9.0, values for H2 and CO2 are 1.5 and values for CO and H2O are 0.5.
3
2
5]
35.
(a)
(i)
(ii)
(iii)
no effect;
equal gas moles on each side;
shift to right;
forward reaction absorbs heat/endothermic/OWTTE;
no effect;
catalyst speeds up both forward and reverse reactions equally;
2
2
2
44
(b)
Kc =
[H 2 ][I 2 ]
[HI]2
;
1
Ignore state symbols.
(c)
(i)
−3
[HI] = 0.04 (mol dm );
−3
[I2] = 0.01 (mol dm );
experiment 1
Kc =
(0.01) 2
= 6.25 ×10 − 2 ;
2
(0.04)
ECF from above values.
−3
[H2] = 0.02 (mol dm );
−3
[I2] = 0.02 (mol dm );
experiment 2
Kc =
(ii)
(0.02) 2
= 0.25;
(0.04) 2
6
ECF from above values.
experiment 2 (at higher temperature);
higher Kc value/equilibrium shifted to right;
2
[15]
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
71.
A
D
A
B
B
D
D
D
B
D
C
D
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
D
D
D
D
A
B
C
B
A
C
D
C
+
–
CH3CH2NH2 + H2O → CH3CH2NH3 + OH ;
(ethylamine) more basic/higher basicity/lower pKb;
because of presence of electron-releasing (ethyl or alkyl) group/
N more electron-rich;
+
attracts H (or H from H2O) more easily;
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
B
A
C
A
A
A
B
A
C
C
B
4
[4]
72.
(a)
(i)
(ii)
−3
−3
0.0010 / 1.0×10 (mol dm );
pH = 3; 2
HCl: strong acid/fully dissociated;
CH3COOH : weak acid/partially dissociated;
HCl less concentrated/CH3COOH more concentrated;
+
only one molecule in 100 dissociates in ethanoic acid so [H ]
1/100/OWTTE
(b)
measure electrical conductivity;
strong acids are good conductors/weak acids are poor conductors;
OR
react with magnesium or a named active metal/(metal) carbonate;
hydrogen carbonate/bicarbonate;
strong acids have a faster reaction/more gas bubbles (per unit time)
/more heat produced/weak acids have a slower reaction/less gas
bubbles (per unit time)/less heat produced;
Accept answers based on:
titration curves: namely strong acid and strong base will have an equivalence
point pH of 7 and a weak acid and strong base will have an equivalence point
pH of >7.
OR
temperature change: on neutralization for temperature change: namely,
+
−
neutralization (H + OH ) is exothermic, weak acid is partially dissociated
so some energy used up in dissociation of weak acid − net result, weak acid
would produce less energy/less temperature increase compared to
neutralization of strong acid.
3
2
[7]
45
73.
CH3CH2COOH + H2O
−
+
CH3CH2COO + H ;
−
+
CH3CH2COO + H3O /CH3CH2COOH
required for mark.
−
+
CH3CH2COOH and CH3CH2COO /H3O and H2O;
2
[2]
74.
(a)
(b)
an acid that partially dissociates/ionizes/doesn’t fully dissociate/ionize;
conductivity - propanoic acid will be lower because lower ion concentration
/less dissociated;
reaction with metal/metal carbonate/metal hydrogencarbonate - propanoic
+
acid will react slower/less vigorously because lower [H ]/less dissociated;
reaction with alkali - temperature change will be less for propanoic acid
+
because lower [H ]/less dissociated;
Award [1] mark each for two.
1
2
3]
75.
conductivity;
nitric acid will contain more ions and have a higher conductivity/ethanoic acid
will have fewer ions and have a lower conductivity;
rate of reaction with metal/carbonate/hydrogencarbonate;
nitric acid will react more rapidly/produce bubbles faster/ethanoic
acid will react less rapidly/produce bubbles more slowly;
reaction with alkali;
temperature change will be less for ethanoic acid;
Accept any two methods and explanations from above.
4
[4]
76.
(i)
(ii)
HCl/X is strong and CH3COOH/Z is weak;
HCl/X is fully dissociated and CH3COOH is slightly dissociated;
+
[H ] is greater in HCl/X than in CH3COOH/Z;
Any two for [1] each.
a factor of 100;
2
1
[3]
77.
Brønsted-Lowry acid
a proton donor;
Lewis acid
electron pair acceptor;
Brønsted-Lowry acid
Any suitable equation;
Lewis acid − BF3/AlCl3/transition metal ions that form complex ion
with ligands;
For example
2+
2+
−
BF3 + NH3 → BF3NH3/Cu + 4NH3 → [Cu(NH3)4] /AlCl3 + Cl →
Or any suitable equation.
AlCl 4− ;
5
[5]
78.
5
vinegar and factor of 10 ;
[1]
79.
HCl/H2SO4/HNO3/any strong acid;
CH3COOH/H2CO3/any weak acid;
Measure pH − the strong acid has the lower pH;
Accept universal indicator and two correct colours.
Measure (electrical) conductivity − this is greater for the stronger acid;
Add magnesium/carbonate − more gas bubbles with the stronger acid/Mg or
carbonate would disappear faster with stronger acid;
[5]
Brønsted-Lowry acid
proton donor/OWTTE;
+
CH3COOH and H3O ;
Lewis base
electron pair donor/OWTTE;
−
H2O and CH3COO ;
80.
4
[4]
81.
(a)
(i)
(ii)
(b)
(i)
+
−
Kw = [H ][OH ];
+
−7
−3
[H ] = 1.5×10 (mol dm );
Accept answer in range 1.5 to 1.55.
CH3CH(OH)COOH + H2O
−
+
CH3CH(OH)COO + H3O ;
1
1
1
46
Ignore state symbols even if incorrect.
The double arrow is necessary for the mark.
ka =
(ii)
[CH 3 CH(OH)COO − ][H +
;
[CH 3 CH(OH)COOH]
+
+
Allow [H3O ] for [H ] in the expression.
−3
+
5.3×10 = [H ];
pH = 2.3;
+
Allow ECF pH based on wrong [H ] in the value, award [1].
Award [2] for correct pH.
pH = 3.85;
Accept answer in range 3.8 to 3.9.
(iii)
(iv)
1
2
1
[7]
bromophenol blue is blue and phenol red is yellow;
pH of 4.8 is above range of bromophenol blue/bromphenol blue shows
its alkaline colour/OWTTE;
pH of 4.8 is below range of phenol red/phenol red shows its acidic
colour/OWTTE;
82.
3
[3]
Ka =
83.
[CH 3 COO − ][H + ]
+
[CH 3 COOH] /rearrangement for [H ];
[H + ] =
1.74 ×10 −5 × 0.0500
= 8.70 ×10 −6 (mol dm −3 ) ;
0.100
+
pH ( = −log[H ]) = 5.06;
OR
pH =
p k a + log
pH = 4.76 + log
3
[CH 3 COO − ]
;
[CH 3 COOH]
 0.10 

;
 0.05 
pH = 5.06;
Accept answer in range 5.0 to 5.1.
+
ECF from [H ].
Award [3] for correct final answer.
[3]
84.
weak acid + salt of weak acid/weak acid + conjugate base.
Accept equivalent descriptions of a basic buffer.
the solution resists pH change;
Do not accept pH does not change.
when small amounts of acid or base are added;
Only award if previous answer correct.
[3]
85.
(a)
(i)
(ii)
(b)
+
−
NH3 + H2O
NH4 + OH ;
Do not penalise →
Do not accept NH4OH
Kb =
[NH 4 + ][OH − ]
;
[NH 3 ]
1
1
−4.75
−5
Kb = 10
= 1.78×10 ;
[OH − ] = 1.78 ×10 −5 × 0.2 = (1.89 ×10 −3 );
−
pOH = −log[OH ] = 2.72;
Accept answer in range 2.68 to 2.76.
Correct answer scores [3].
Apply ECF throughout this part.
3
[5]
86.
(i)
(ii)
+
pH = − log[H ];
curve should include the following:
starting pH = 1;
3
equivalence point: 25.0 cm of NaOH;
1
47
pH at equivalence point = 7;
pH to finish = 12−13;
pH
13
7
1
Volume / cm3
25
4
Penalise [1] if profile incorrect.
(iii)
−4.76
−5
Ka = 10
/1.74×10 ;
+2
−5
Ka = [H ] ÷[CH3COOH]/1.74×10 =
[H + ] 2
;
0.100
+
−3
−3
[H ] = 1.32×10 (mol dm );
starting pH = 2.88;
Accept 3 sig. fig.
Award [4] for correct pH.
Allow ECF.
pH at equivalence point: 8−9;
5
[10]
87.
(i)
(ii)
HIn is a weak acid;
+
−
H + In and two colours indicated;
HIn
In acid equilibrium moves left or vice versa;
phenolphthalein/phenol red/bromothymol blue;
colour change of indicator occurs within the range of pH at equivalence
point/on vertical part of graph;
3
2
[5]
88.
(i)
(ii)
specific examples of weak base and its salt/specific strong acid and
weak base;
Name of structure acceptable.
e.g. NH3 and NH4Cl.
pH changes very little/most acid neutralized by base;
equation from (i);
Any other suitable example.
+
+
+
+
e.g. NH3 + H → NH 4 /NH4OH + H → NH 4 + H2O.
1
2
[3]
89.
acidic;
+
is (weak) acid due to the formation of H /
3+
2+
+
[Al(H2O)5(OH)] + H ;
[Al(H2O)6]
[Al(H2O6)]
3+
2
[2]
90.
(i)
(ii)
(iii)
(iv)
−3
0.1 (mol dm );
3;
3
28(.0) (cm );
−3
nNaOH/HNO3 ( = 0.100×0.0280) = 2.80×10 (mol);
ECF from value in (iii).
−3
−3
[HNO3] (= 2.80×10 ÷0.025) = 0.112 (mol dm );
ECF from n above.
Correct final answer scores [2].
1
1
1
2
[5]
91.
(a)
(b)
+
−
NH3(aq) + H2O(l)
N H 4 (aq) + OH (aq);
Ignore state symbols and accept →.
Kb =
[NH 4+ ][OH − ]
[NH 3 ]
1
1
48
(c)
−
−3
[OH ] = 2.1×10
+
−12
pOH = 2.7/[H ] = 4.8×10
pH = 11.3;
Allow ECF for the value of pOH and pH.
3
[5]
92.
(a)
(b)
NaOH is a strong base/NH3 is a weak base;
NaOH completely dissociates/ionizes;
NH3 partially dissociates/ionizes;
−
+
−
+
pH 14 has high [OH ]/low [H ]/pH 12 has lower [OH ]/higher [H ];
+
−
NaOH → Na + OH ;
+
−
NH4 + OH ; (
required)
NH3 + H2O
NaOH + HNO3 → NaNO3 + H2O;
1 pH/pOH unit represents a 10 fold change in concentration;
−3
So if a 1.0 mol dm NaOH solution has a pH of 14
−3
then a 0.10 mol dm solution will have a pH of 13;
Units needed for the mark.
Award [2] for correct final answer.
3
18.0 cm ;
(i)
(ii)
(iii)
(
0.10 × 20.0
=) 0.11 mol dm −3 ;
18.0
Allow ECF from an incorrect value of concentration in part (ii).
3
18.0 cm ;
(iv)
5
1
2
2
1
[11]
93.
(i)
(ii)
a solution which resists change in pH;
when a small amount of strong acid or base is added to it;
react excess ammonia with nitric acid;
stated volumes with about 50% more ammonia solution;
gives a solution containing the weak base and its salt with the acid/
+
NH4 and NH3;
3
3
nd
Accept suitable volumes from about 20 cm to about 500 cm for 2 mark.
2
3
[5]
94.
(a)
−
+
C6H5COOH + H2O
C6H5COO + H3O ;
Ignore state symbols.
Accept C6H5COOH
1
−
+
C6H5COO + H .
needed for mark.
(b)
(c)
−4.20
−5
−3
Ka (= 10
) = 6.31×10 (mol dm );
Units not needed for mark, but penalize incorrect units.
Ka
=
1
[C 6 H 5 COO − ][H + ] [C 6 H 5 CO 2− ][H 3 O + ]
/
;
[C 6 H 5 COOH]
[C 6 H 5 CO 2 H]
+
−3
−3
[H ] = √ Ka[C6H5COOH]/3.55×10 (mol dm );
pH = 2.45;
+
Apply ECF from (b) and from [H ] to pH.
Correct final answer scores [3].
3
[5]
95.
(pKa (propanoic) = 4.87)
ka
=
[CH 3 CH 2 COO − ][H 3 O + ]
;
[CH 3 CH 2 COOH]
+
−3
−3
[H3O ]= 1.16×10 (mol dm );
pH = 2.94;
Award [3] for correct answer.
3
[3]
96.
(a)
+
−
+
−
(Kw = ) [H ][OH ]/[H3O ] [OH ];
−14
−14
= 2.89×10
/ 2.9×10
;
2
49
Units not needed.
(b)
pH = 6.8;
1
Accept answer in range 6.7 to 6.8.
(c)
neutral;
+
−
+
−
[H ] = [OH ]/[H3O ] = [OH ]/OWTTE;
2
[5]
97.
(i)
13
pH
7
1
25
(ii)
/ cm 3 Hcl
graph starting at pH < 13;
Award [0] for pH=13.
equivalence point pH < 7;
Accept anything between 4 and 6
bottom end of graph: pH between 3 and 1;
−
−3
NH3 is a weak base/partially dissociated/[OH ]</<<0.10mol dm
(therefore, pH < 13);
+
+
+
+
NH4 formed is a weak acid/NH4
NH3 + H /NH4 dissociates into
a weak base and a strong acid (thus acidic at equivalence point);
HCl is a strong acid, thus graph finishes close to pH = 1;
methyl orange/bromocresol green/bromophenol blue/methyl red;
pKa of indicator centred around pH at equivalence/end point/indicator
pH range falls where there is a sharp pH change/OWTTE;
6
2
[8]
98.
(i)
(ii)
(iii)
(iv)
weak acid and salt of the weak acid/its conjugate base;
HCl/HNO3/H2SO4;
Amount < 0.10 mol for HCl/HNO3/< 0.05 mol for H2SO4;
−
+
(added) OH reacts with NH4 present/acid of buffer;
+
(added) H reacts with NH3 present/base of buffer;
−
+
OH + NH4 → NH3 + H2O (strong base replaced by weak base);
+
+
H + NH3 → NH4 (strong acid replaced by weak acid);
+
−
NH3(aq) + H2O(l)
NH4 (aq) + OH (aq);
States not required for mark
Kb =
[NH 4 + ][OH − ]
;
[NH 3 ]
1
2
4
2
[9]
99.
(a)
(i)
(ii)
(iii)
(b)
3+
acidic and [Fe(H2O)6] is a weak acid
3+
2+
+
[Fe(H2O)6] (aq) → [Fe(OH)(H2O)5] (aq) + H (aq);
“FeCl3 is acidic” is not acceptable.
neutral and NaNO3/sodium nitrate is formed from strong base
and strong acid/ions do not hydrolyze;
2–
alkaline and CO3 is a weak base/
2–
–
–
CO3 (aq) + H2O(l) → HCO3 (aq) + OH (aq);
Award [1] only for correct identification of solutions as acidic, neutral and alkaline
only, without explanation.
1
1
1
nitrogen and sulfur;
50
kills/harms fish/aquatic life in lakes/rivers;
leaching of soils damages plant life/trees;
3
[6]
100.
(a)
2NH3(aq) + H2SO4(aq) → (NH4)2SO4(aq);
Accept correct equation with NH4OH instead of NH3.
n(H2SO4) = 0.0201×0.150 (mol);
–3
n(NH3) = 6.03×10 (mol);
–3
[NH3] = 0.241 (mol dm );
Award [3] for the correct final answer for the concentration calculation.
(b)
bromocresol green;
reaction of weak base and strong acid;
pH range of bromocresol green is 3.8 to 5.4/occurs at pH < 7;
(c)
(i)
4
3
–4.75
–5
Kb = 10
= 1.78×10 ;
Kb =
[ NH 4+ ][OH − ]
/[OH − ] = K b [ NH 3 ];
[ NH 3 ]
−5
–
[OH ] = 1.78 × 10 × 0.121;
pOH = 2.83;
Award [4] for the correct final answer.
4
–
Allow ECF, for example any correct conversion of [OH ] to pOH.
(ii)
(iii)
a solution which resists change in pH/changes pH very slightly;
when small amounts of acid or base are added;
weak acid and its salt/weak acid and its conjugate base;
3
n(NH3) = 0.00500 (mol) and n(HCl) = 0.00250 (mol);
[ NH 4+ ] = [ NH 3 ];
–
–5
[OH ] = Kb = 1.78×10 ;
(pOH = 4.75 so) pH = 9.25 (allow 9.2 to 9.3);
Award [4] for correct final answer.
Accept other valid methods.
4
[18]
51