Topic 1 Q and A

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Topic 1 Q and A [145 marks]
1.
How many atoms of nitrogen are there in 0.50 mol of (NH 4)2CO3?
[1 mark]
A. 1
B. 2
C. 3.01 × 10 23
D. 6.02 × 10 23
Markscheme
D
Examiners report
[N/A]
2.
What is the value of x when 32.2 g of Na 2SO4•xH2O are heated leaving 14.2 g of anhydrous Na 2SO4? M r(H2O) = 18; M r(Na 2SO4) = [1 mark]
142.
Na2SO4•xH2O (s) → Na 2SO4 (s) + xH2O (g)
A. 0.1
B. 1
C. 5
D. 10
Markscheme
D
Examiners report
[N/A]
3.
How many grams of sodium azide, NaN 3, are needed to produce 68.1 dm 3 of N 2 (g) at STP?
Molar volume at STP = 22.7 dm3 mol –1; M r(NaN 3) = 65.0
2NaN3 (s) → 3N 2 (g) + 2Na (s)
A. 32.5
B. 65.0
C. 130.0
D. 195.0
Markscheme
C
[1 mark]
Examiners report
[N/A]
4.
What is the sum of the coefficients when the following equation is balanced using the smallest whole numbers?
[1 mark]
__C6H12O6 (aq) → __C 2H5OH (aq) + __CO 2 (g)
A. 4
B. 5
C. 9
D. 10
Markscheme
B
Examiners report
[N/A]
5.
Which compound has the greatest percentage by mass of nitrogen atoms?
A.
N2H4
B.
NH3
C.
N 2O4
D.
NaNO 3
[1 mark]
Markscheme
A
Examiners report
[N/A]
6.
Which statements about mixtures are correct?
I.
The components may be elements or compounds.
II. All components must be in the same phase.
III. The components retain their individual properties.
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
Markscheme
B
[1 mark]
Examiners report
[N/A]
7.
5.0 cm3 of 2.00 mol dm–3 sodium carbonate solution, Na2CO3(aq), was added to a volumetric flask and the volume was made up to
[1 mark]
500 cm3 with water. What is the concentration, in mol dm–3, of the solution?
A.
0.0050
B.
0.0040
C.
0.020
D.
0.010
Markscheme
C
Examiners report
[N/A]
8.
What is the expression for the volume of hydrogen gas, in dm3, produced at STP when 0.30 g of magnesium reacts with excess
hydrochloric acid solution?
[1 mark]
Mg(s) + 2HCl(aq) → MgCl 2(aq) + H2(g)
Molar volume of an ideal gas at STP = 22.7 dm 3 mol −1
A.
0.30 ×2× 22.7
24.31
B.
0.30 × 22.7
24.31
C.
0.30 × 24.31
22.7
D.
0.30 × 22.7
24.31×2
Markscheme
B
Examiners report
[N/A]
9.
What is the sum of the coefficients when the equation is balanced with whole numbers?
—C8H18(g)
A.
26.5
B.
30
C.
53
D.
61
+ —O2(g) →
—CO(g)
+ —H2O(l)
Markscheme
C
[1 mark]
Examiners report
[N/A]
10.
How many moles of oxygen atoms are there in 0.500 mol of hydrated iron(II) ammonium sulfate, (NH 4)2Fe(SO4)2•6H2O(s)?
A.
4.00
B.
7.00
C.
8.00
D.
14.00
[1 mark]
Markscheme
B
Examiners report
[N/A]
11.
What is the maximum volume, in dm 3, of CO 2(g) produced when 1.00 g of CaCO3(s) reacts with 20.0 cm 3 of 2.00 mol dm–3
HCl(aq)?
[1 mark]
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
Molar volume of gas = 22.7 dm 3 mol –1; M r(CaCO 3) = 100.00
× 2.0
× 20.0
× 22.7
1000
A.
1
2
B.
20.0 × 2.0
1000
C.
1.0
100.00
× 22.7
D.
1.0
100.00
× 2 × 22.7
× 22.7
Markscheme
C
Examiners report
[N/A]
12.
Which factors affect the molar volume of an ideal gas?
I.
Pressure
II. Temperature
III. Empirical formula
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
Markscheme
A
[1 mark]
Examiners report
[N/A]
13.
Which solution neutralizes 50.0 cm 3 of 0.120 mol dm –3 NaOH (aq)?
[1 mark]
A. 12.5 cm3 of 0.080 mol dm –3 H3PO4
B. 25.0 cm3 of 0.120 mol dm –3 CH3COOH
C. 25.0 cm 3 of 0.120 mol dm –3 H2SO4
D. 50.0 cm 3 of 0.060 mol dm –3 HNO3
Markscheme
C
Examiners report
[N/A]
14.
What is the pressure, in Pa, inside a 1.0 m 3 cylinder containing 10 kg of H 2 (g) at 25 ºC?
[1 mark]
R = 8.31 J K–1 mol –1; pV = nRT
A.
1× 104× 8.31 × 25
1.0× 103
B.
5× 102× 8.31 × 298
1.0
C.
1× 8.31 × 25
1.0× 103
D.
5× 103× 8.31 × 298
1.0
Markscheme
D
Examiners report
[N/A]
15. A compound with M r = 102 contains 58.8 % carbon, 9.80 % hydrogen and 31 % oxygen by mass.
What is its molecular formula?
Ar: C = 12.0; H = 1.0; O = 16.0
A. C2H14O4
B. C3H4O4
C. C5H10O2
D. C6H14O
Markscheme
C
[1 mark]
Examiners report
[N/A]
A student titrated an ethanoic acid solution, CH 3COOH (aq), against 50.0 cm 3 of 0.995 mol dm –3 sodium hydroxide, NaOH (aq), to
determine its concentration.
The temperature of the reaction mixture was measured after each acid addition and plotted against the volume of acid.
16a. Using the graph, estimate the initial temperature of the solution.
[1 mark]
Markscheme
21.4 °C
Accept values in the range of 21.2 to 21.6 °C.
Examiners report
[N/A]
16b. Determine the maximum temperature reached in the experiment by analysing the graph.
Markscheme
29.0 «°C»
Accept range 28.8 to 29.2 °C.
Examiners report
[N/A]
–3
[1 mark]
–3
16c. Calculate the concentration of ethanoic acid, CH 3COOH, in mol dm .
[2 marks]
Markscheme
ALTERNATIVE 1
«volume CH3COOH =» 26.0 «cm3»
«[CH3COOH] = 0.995 mol dm –3 \( \times \frac{{50.0\,{\text{cm 3}}}}{{26.0\,{\text{cm3}}}} = \)» 1.91 «mol dm−3 »
ALTERNATIVE 2
«n(NaOH) =0.995 mol dm–3 x 0.0500 dm3 =» 0.04975 «mol»
«[CH3COOH] =
0.04975
0.0260
dm3 =» 1.91 «mol dm–3»
Accept values of volume in range 25.5 to 26.5 cm 3.
Award [2] for correct final answer.
Examiners report
[N/A]
16d. Determine the heat change, q, in kJ, for the neutralization reaction between ethanoic acid and sodium hydroxide.
Assume the specific heat capacities of the solutions and their densities are those of water.
Markscheme
«total volume = 50.0 + 26.0 =» 76.0 cm3 AND «temperature change 29.0 – 21.4 =» 7.6 «°C»
«q = 0.0760 kg x 4.18 kJ kg –1 K–1 x 7.6 K =» 2.4 «kJ»
Award [2] for correct final answer.
[2 marks]
Examiners report
[N/A]
16e.
Calculate the enthalpy change, ΔH, in kJ mol –1, for the reaction between ethanoic acid and sodium hydroxide.
Markscheme
«n(NaOH) = 0.995 mol dm–3 x 0.0500 dm3 =» 0.04975 «mol»
OR
«n(CH3COOH) = 1.91 mol dm –3 x 0.0260 dm3 =» 0.04966 «mol»
«ΔH = −
2.4 kJ
0.04975 mol
=» –48 / –49 «kJ mol –1»
Award [2] for correct final answer.
Negative sign is required for M2.
Examiners report
[N/A]
[2 marks]
Curves X and Y were obtained when a metal carbonate reacted with the same volume of ethanoic acid under two different conditions.
16f.
Explain the shape of curve X in terms of the collision theory.
[2 marks]
Markscheme
«initially steep because» greatest concentration/number of particles at start
OR
«slope decreases because» concentration/number of particles decreases
volume produced per unit of time depends on frequency of collisions
OR
rate depends on frequency of collisions
Examiners report
[N/A]
16g. Suggest one possible reason for the differences between curves X and Y.
[1 mark]
Markscheme
mass/amount/concentration of metal carbonate more in X
OR
concentration/amount of CH 3COOH more in X
Examiners report
[N/A]
Menthol is an organic compound containing carbon, hydrogen and oxygen.
17a.
Complete combustion of 0.1595 g of menthol produces 0.4490 g of carbon dioxide and 0.1840 g of water. Determine the empirical
[3 marks]
formula of the compound showing your working.
Markscheme
carbon: «
0.4490 g
44.01 g mo l−1
» = 0.01020 «mol» / 0.1225 «g»
OR
hydrogen: « 0.1840×2 » = 0.02042 «mol» / 0.0206 «g»
18.02
oxygen: «0.1595 – (0.1225 + 0.0206)» = 0.0164 «g» / 0.001025 «mol»
empirical formula: C 10H20O
Award [3] for correct final answer.
Examiners report
[N/A]
3
3
17b. 0.150 g sample of menthol, when vaporized, had a volume of 0.0337 dm at 150 °C and 100.2 kPa. Calculate its molar mass
showing your working.
[2 marks]
Markscheme
temperature = 423 K
OR
«M =
«M =
mRT
pV
0.150 g× 8.31 J K−1 mol−1× 423 K
100.2 kPa× 0.0337 dm3
=» 156 «g mol –1»
Award [1] for correct answer with no working shown.
Accept “pV = nRT AND n =
m
”
M
for M1.
Examiners report
[N/A]
Titanium is a transition metal.
18a.
Describe the bonding in metals.
[2 marks]
Markscheme
electrostatic attraction
between «a lattice of» metal/positive ions/cations AND «a sea of» delocalized electrons
Accept mobile electrons.
Do not accept “metal atoms/nuclei”.
[2 marks]
Examiners report
[N/A]
18b.
Titanium exists as several isotopes. The mass spectrum of a sample of titanium gave the following data:
Calculate the relative atomic mass of titanium to two decimal places.
Markscheme
(46× 7.98)+(47× 7.32)+(48× 73.99)+(49× 5.46)+(50× 5.25)
100
= 47.93
Answer must have two decimal places with a value from 47.90 to 48.00.
Award [2] for correct final answer.
Award [0] for 47.87 (data booklet value).
[2 marks]
Examiners report
[N/A]
[2 marks]
18c.
State the number of protons, neutrons and electrons in the
48Ti
22
atom.
[1 mark]
Markscheme
Protons: 22 AND Neutrons: 26 AND Electrons: 22
[1 mark]
Examiners report
[N/A]
18d.
State the full electron configuration of the
48Ti2+
22
Markscheme
1s22s22p 63s23p 63d 2
[1 mark]
Examiners report
[N/A]
ion.
[1 mark]
18e.
Explain why an aluminium-titanium alloy is harder than pure aluminium.
[2 marks]
Markscheme
titanium atoms/ions distort the regular arrangement of atoms/ions
OR
titanium atoms/ions are a different size to aluminium «atoms/ions»
prevent layers sliding over each other
Accept diagram showing different sizes of atoms/ions.
[2 marks]
Examiners report
[N/A]
18f.
State the type of bonding in potassium chloride which melts at 1043 K.
Markscheme
ionic
OR
«electrostatic» attraction between oppositely charged ions
[1 mark]
Examiners report
[N/A]
[1 mark]
18g. A chloride of titanium, TiCl 4, melts at 248 K. Suggest why the melting point is so much lower than that of KCl.
[1 mark]
Markscheme
«simple» molecular structure
OR
weak«er» intermolecular bonds
OR
weak«er» bonds between molecules
Accept specific examples of weak bonds such as London/dispersion and van der Waals.
Do not accept “covalent”.
[1 mark]
Examiners report
[N/A]
TiCl4 reacts with water and the resulting titanium(IV) oxide can be used as a smoke screen.
18h.
Formulate an equation for this reaction.
Markscheme
TiCl4(l) + 2H2O(l) → TiO2(s) + 4HCl(aq)
correct products
correct balancing
Accept ionic equation.
Award M2 if products are HCl and a compound of Ti and O.
[2 marks]
Examiners report
[N/A]
[2 marks]
18i.
Suggest one disadvantage of using this smoke in an enclosed space.
[1 mark]
Markscheme
HCl causes breathing/respiratory problems
OR
HCl is an irritant
OR
HCl is toxic
OR
HCl has acidic vapour
OR
HCl is corrosive
Accept “TiO2 causes breathing problems/is an irritant”.
Accept “harmful” for both HCl and TiO2.
Accept “smoke is asphyxiant”.
[1 mark]
Examiners report
[N/A]
Vanadium, another transition metal, has a number of different oxidation states.
19a. Determine the oxidation state of vanadium in each of the following species.
[2 marks]
Markscheme
V2O5: +5
VO2+ : +4
Do not penalize incorrect notation twice.
[2 marks]
Examiners report
[N/A]
19b.
Formulate an equation for the reaction between VO 2+ (aq) and V2+ (aq) in acidic solution to form V 3+ (aq).
[1 mark]
Markscheme
VO2+ (aq) + V2+ (aq) + 2H+(aq) → 2V 3+ (aq) + H2O(l)
Accept equilibrium sign.
[1 mark]
Examiners report
[N/A]
Two hydrides of nitrogen are ammonia and hydrazine, N 2H4. One derivative of ammonia is methanamine whose molecular structure is
shown below.
20a. Estimate the H−N−H bond angle in methanamine using VSEPR theory.
[1 mark]
Markscheme
107°
Accept 100° to < 109.5°.
Literature value = 105.8°
[1 mark]
Examiners report
[N/A]
20b.
Ammonia reacts reversibly with water.
[2 marks]
NH3(g) + H2O(l) ⇌ NH4+(aq) + OH−(aq)
Explain the effect of adding H+(aq) ions on the position of the equilibrium.
Markscheme
removes/reacts with OH −
moves to the right/products «to replace OH− ions»
Accept ionic equation for M1.
[2 marks]
Examiners report
[N/A]
20c. Hydrazine reacts with water in a similar way to ammonia. Deduce an equation for the reaction of hydrazine with water.
[1 mark]
Markscheme
N2H4(aq) + H2O(l) ⇌ N2H5+(aq) + OH–(aq)
Accept N2H4(aq) + 2H2O(l)
⇌ N2H62+ (aq) + 2OH–(aq).
Equilibrium sign must be present.
[1 mark]
Examiners report
[N/A]
20d.
Outline, using an ionic equation, what is observed when magnesium powder is added to a solution of ammonium chloride.
Markscheme
bubbles
OR
gas
OR
magnesium disappears
2NH4+(aq) + Mg(s) → Mg 2+ (aq) + 2NH3(aq) + H2(g)
Do not accept “hydrogen” without reference to observed changes.
Accept "smell of ammonia".
Accept 2H +(aq) + Mg(s) → Mg 2+ (aq) + H2(g)
Equation must be ionic.
[2 mark]
Examiners report
[N/A]
[2 marks]
20e.
Hydrazine has been used as a rocket fuel. The propulsion reaction occurs in several stages but the overall reaction is:
[1 mark]
N2H4(l) → N2(g) + 2H2(g)
Suggest why this fuel is suitable for use at high altitudes.
Markscheme
no oxygen required
[1 mark]
Examiners report
[N/A]
20f.
Determine the enthalpy change of reaction, Δ H, in kJ, when 1.00 mol of gaseous hydrazine decomposes to its elements. Use bond
[3 marks]
enthalpy values in section 11 of the data booklet.
N2H4(g) → N2(g) + 2H2(g)
Markscheme
bonds broken:
E(N–N) + 4E(N–H)
OR
158 «kJ mol –1» + 4 x 391 «kJ mol –1» / 1722 «kJ»
bonds formed:
E(N≡N) + 2E(H–H)
OR
945 «kJ mol –1» + 2 x 436 «kJ mol –1» / 1817 «kJ»
«ΔH = bonds broken – bonds formed = 1722 – 1817 =» –95 «kJ»
Award [3] for correct final answer.
Award [2 max] for +95 «kJ».
[3 marks]
Examiners report
[N/A]
20g.
The standard enthalpy of formation of N 2H4(l) is +50.6 kJ mol −1 . Calculate the enthalpy of vaporization, ΔHvap, of hydrazine in kJ
mol −1 .
N2H4(l) → N2H4(g)
(If you did not get an answer to (f), use −85 kJ but this is not the correct answer.)
[2 marks]
Markscheme
OR
ΔHvap= −50.6 kJ mol −1 − (−95 kJ mol −1 )
«ΔHvap =» +44 «kJ mol −1 »
Award [2] for correct final answer.
Award [1 max] for −44 «kJ
mol −1 ».
Award [2] for:
ΔHvap − = 50.6 kJ
mol −1 − (−85 kJ
mol −1 ) + = 34 «kJ
mol −1 ».
Award [1 max] for −34 «kJ
mol −1 ».
[2 marks]
Examiners report
[N/A]
Hydrazine is used to remove oxygen from water used to generate steam or hot water.
N2H4(aq) + O2(aq) → N 2(g) + 2H2O(l)
The concentration of dissolved oxygen in a sample of water is 8.0 × 10 −3 g dm−3 .
20h.
Calculate, showing your working, the mass of hydrazine needed to remove all the dissolved oxygen from 1000 dm 3 of the sample.
[3 marks]
Markscheme
total mass of oxygen «= 8.0 x 10–3 g dm–3 x 1000 dm3» = 8.0 «g»
n(O2) « =
8.0 g
32.00 g mo l−1
=» 0.25 «mol»
OR
n(N 2H4) = n(O2)
«mass of hydrazine = 0.25 mol x 32.06 g mol –1 =» 8.0 «g»
Award [3] for correct final answer.
[3 marks]
Examiners report
[N/A]
20i.
Calculate the volume, in dm3, of nitrogen formed under SATP conditions. (The volume of 1 mol of gas = 24.8 dm
Markscheme
«n(N2H4) = n(O2) =
8.0 g
32.00 g mo l−1
=» 0.25 «mol»
«volume of nitrogen = 0.25 mol x 24.8 dm 3 mol –1» = 6.2 «dm 3»
Award [1] for correct final answer.
[1 mark]
Examiners report
[N/A]
3
at SATP.)
[1 mark]
This question is about carbon and chlorine compounds.
21a.
Ethane, C2H6, reacts with chlorine in sunlight. State the type of this reaction and the name of the mechanism by which it occurs.
Markscheme
substitution AND «free-»radical
OR
substitution AND chain
Award [1] for “«free-»radical substitution” or “S R” written anywhere in the answer.
[1 mark]
Examiners report
[N/A]
[1 mark]
21b. Formulate equations for the two propagation steps and one termination step in the formation of chloroethane from ethane.
Markscheme
Two propagation steps:
C2H6 + •Cl → C 2H5• + HCl
C2H5• + Cl2 → C 2H5Cl + •Cl
One termination step:
C2H5• + C2H5• → C 4H10
OR
C2H5• + •Cl → C 2H5Cl
OR
•Cl + •Cl → Cl2
Accept radical without • if consistent throughout.
Allow ECF from incorrect radicals produced in propagation step for M3.
[3 marks]
Examiners report
[N/A]
[3 marks]
21c.
One possible product, X, of the reaction of ethane with chlorine has the following composition by mass:
carbon: 24.27%, hydrogen: 4.08%, chlorine: 71.65%
Determine the empirical formula of the product.
Markscheme
C=
24.27
12.01
= 2.021 AND H =
4.08
1.01
= 4.04 AND Cl =
«hence» CH2Cl
Accept
24.27
:
12.01
4.08
:
1.01
71.65
.
35.45
Do not accept C2H4Cl2.
Award [2] for correct final answer.
[2 marks]
Examiners report
[N/A]
1
71.65
35.45
= 2.021
[2 marks]
21d.
The mass and 1H NMR spectra of product X are shown below. Deduce, giving your reasons, its structural formula and hence the
name of the compound.
[3 marks]
Markscheme
molecular ion peak(s) «about» m/z 100 AND «so» C2H4Cl2 «isotopes of Cl»
two signals «in 1H NMR spectrum» AND «so» CH3CHCl2
OR
«signals in» 3:1 ratio «in 1H NMR spectrum» AND «so» CH3CHCl2
OR
one doublet and one quartet «in 1H NMR spectrum» AND «so» CH3CHCl2
1,1-dichloroethane
Accept “peaks” for “signals”.
Allow ECF for a correct name for M3 if an incorrect chlorohydrocarbon is identified
[3 marks]
Examiners report
[N/A]
21e.
Chloroethene, C2H3Cl, can undergo polymerization. Draw a section of the polymer with three repeating units.
Markscheme
Continuation bonds must be shown.
Ignore square brackets and “n”.
Accept
.
Accept other versions of the polymer, such as head to head and head to tail.
Accept condensed structure provided all C to C bonds are shown (as single).
[1 mark]
[1 mark]
Examiners report
[N/A]
There are many oxides of silver with the formula Ag xOy. All of them decompose into their elements when heated strongly.
22a.
After heating 3.760 g of a silver oxide 3.275 g of silver remained. Determine the empirical formula of Ag xOy.
[2 marks]
Markscheme
n(Ag) = «
3.275 g
107.87 g mol
=» 0.03036 «mol»
AND
n(O) = «
3.760 g−3.275 g
16.00 g mo l−1
=
0.485
16.00
=» 0.03031 «mol»
« 0.03036 ≈ 1 / ratio of Ag to O approximately 1 : 1, so»
0.03031
AgO
Accept other valid methods for M1.
Award [1 max] for correct empirical formula if method not shown.
[2 marks]
Examiners report
[N/A]
22b.
Suggest why the final mass of solid obtained by heating 3.760 g of Ag xOy may be greater than 3.275 g giving one design
improvement for your proposed suggestion. Ignore any possible errors in the weighing procedure.
[2 marks]
Markscheme
temperature too low
OR
heating time too short
OR
oxide not decomposed completely
heat sample to constant mass «for three or more trials»
Accept “not heated strongly enough”.
If M1 as per markscheme, M2 can only be awarded for constant mass technique.
Accept "soot deposition" (M1) and any suitable way to reduce it (for M2).
Accept "absorbs moisture from atmosphere" (M1) and "cool in dessicator" (M2).
Award [1 max] for reference to impurity AND design improvement.
[2 marks]
Examiners report
[N/A]
22c.
Naturally occurring silver is composed of two stable isotopes,
107Ag
The relative atomic mass of silver is 107.87. Show that isotope
Markscheme
Ar closer to 107/less than 108 «so more 107Ag»
OR
Ar less than the average of (107 + 109) «so more
Accept calculations that gives greater than 50%
[1 mark]
Examiners report
[N/A]
107Ag»
107Ag.
and 109Ag.
107Ag
is more abundant.
[1 mark]
22d.
Some oxides of period 3, such as Na 2O and P4O10, react with water. A spatula measure of each oxide was added to a separate
100 cm3 flask containing distilled water and a few drops of bromothymol blue indicator.
[3 marks]
The indicator is listed in section 22 of the data booklet.
Deduce the colour of the resulting solution and the chemical formula of the product formed after reaction with water for each oxide.
Markscheme
Do not accept name for the products.
Accept “Na + + OH–” for NaOH.
Ignore coefficients in front of formula.
[3 marks]
Examiners report
[N/A]
22e. Explain the electrical conductivity of molten Na 2O and P4O10.
[2 marks]
Markscheme
«molten» Na 2O has mobile ions/charged particles AND conducts electricity
«molten» P4O10 does not have mobile ions/charged particles AND does not conduct electricity/is poor conductor of electricity
Do not award marks without concept of mobile charges being present.
Award [1 max] if type of bonding or electrical conductivity correctly identified in each compound.
Do not accept answers based on electrons.
Award [1 max] if reference made to solution.
[2 marks]
Examiners report
[N/A]
22f.
Outline the model of electron configuration deduced from the hydrogen line emission spectrum (Bohr’s model).
[2 marks]
Markscheme
electrons in discrete/specific/certain/different shells/energy levels
energy levels converge/get closer together at higher energies
OR
energy levels converge with distance from the nucleus
Accept appropriate diagram for M1, M2 or both.
Do not give marks for answers that refer to the lines in the spectrum.
[2 marks]
Examiners report
[N/A]
2+
4+
An acidic sample of a waste solution containing Sn 2+ (aq) reacted completely with K 2Cr2O7 solution to form Sn 4+ (aq).
23a.
State the oxidation half-equation.
[1 mark]
Markscheme
Sn2+ (aq) → Sn 4+ (aq) + 2e –
Accept equilibrium sign.
Accept Sn2+ (aq) – 2e – → Sn 4+ (aq).
[1 mark]
Examiners report
[N/A]
23b.
Deduce the overall redox equation for the reaction between acidic Sn2+ (aq) and Cr2O72–(aq), using section 24 of the data booklet.
Markscheme
Cr2O72–(aq) + 14H +(aq) + 3Sn2+ (aq) → 2Cr 3+ (aq) + 7H2O(l) + 3Sn4+ (aq)
Accept equilibrium sign.
[1 mark]
Examiners report
[N/A]
[1 mark]
23c.
Calculate the percentage uncertainty for the mass of K2Cr2O7(s) from the given data.
[1 mark]
Markscheme
«13.239 g ± 0.002 g so percentage uncertainty» 0.02 «%»
Accept answers given to greater precision, such as 0.0151%.
[1 mark]
Examiners report
[N/A]
3
23d. The sample of K2Cr2O7(s) in (i) was dissolved in distilled water to form 0.100 dm solution. Calculate its molar concentration.
Markscheme
« [K2Cr2O7] =
13.239 g
294.20 g mo l−1× 0.100 dm3
=» 0.450 «mol dm–3»
[1 mark]
Examiners report
[N/A]
3
3
2+
[1 mark]
23e.
10.0 cm3 of the waste sample required 13.24 cm 3 of the K2Cr2O7 solution. Calculate the molar concentration of Sn2+ (aq) in the
waste sample.
[2 marks]
Markscheme
n(Sn 2+ ) = «0.450 mol dm–3 x 0.01324 dm 3 x
«[Sn2+ ]
=
0.0179 mol
0.0100 mol
=» 1.79
3 mol
1 mol
=» 0.0179 «mol»
«mol dm–3»
Award [2] for correct final answer.
[2 marks]
Examiners report
[N/A]
Soluble acids and bases ionize in water.
Sodium hypochlorite ionizes in water.
OCl–(aq) + H2O(l) ⇌ OH–(aq) + HOCl(aq)
24a.
Identify the amphiprotic species.
Markscheme
water/H2O
Accept “hydroxide ion/OH –”.
[1 mark]
Examiners report
[N/A]
[1 mark]
24b. Identify one conjugate acid-base pair in the reaction.
[1 mark]
Markscheme
[1 mark]
Examiners report
[N/A]
A solution containing 0.510 g of an unknown monoprotic acid, HA, was titrated with 0.100 mol dm –3 NaOH(aq). 25.0 cm 3 was required
to reach the equivalence point.
24c. Calculate the amount, in mol, of NaOH(aq) used.
Markscheme
«0.100 mol dm–3 x 0.0250 dm3» = 0.00250 «mol»
[1 mark]
Examiners report
[N/A]
[1 mark]
24d.
Calculate the molar mass of the acid.
[1 mark]
Markscheme
«M =
0.510 g
0.00250 mol
=» 204 «g mol –1»
[1 mark]
Examiners report
[N/A]
24e.
Calculate [H+] in the NaOH solution.
[1 mark]
Markscheme
«1.00 x 10–14 = [H+] x 0.100»
1.00 x 10–13 «mol dm–3»
[1 mark]
Examiners report
[N/A]
Analytical chemistry uses instruments to separate, identify, and quantify matter.
25a.
Outline how this spectrum is related to the energy levels in the hydrogen atom.
[1 mark]
Markscheme
electron transfer/transition between high«er» energy level to low«er» energy level
OR
electron transitions into first energy level causes UV series
OR
transition into second energy level causes visible series
OR
transition into third energy level causes infrared series
Accept any of the points shown on a diagram.
Examiners report
[N/A]
25b.
A sample of magnesium has the following isotopic composition.
Calculate the relative atomic mass of magnesium based on this data, giving your answer to two decimal places.
Markscheme
24 x 0.786 + 25 x 0.101 + 26 x 0.113
24.33
Award [2] for correct final answer.
Award [0] for 24.31 with no working (data booklet value).
Examiners report
[N/A]
[2 marks]
25c.
Complete combustion of 0.1595 g of menthol produces 0.4490 g of carbon dioxide and 0.1840 g of water. Determine the empirical
[3 marks]
formula of the compound showing your working.
Markscheme
carbon: «
0.4490 g
44.01 g mo l−1
=» 0.01020 «mol» / 0.1225 «g»
OR
hydrogen: «
0.1840×2
18.02 g mol−1
=» 0.02042 «mol» / 0.0206 «g»
oxygen: «0.1595 – (0.1225 + 0.0206)» = 0.0164 «g» / 0.001025 «mol»
empirical formula: C 10H20O
Award [3] for correct final answer.
Do not award M3 for a hydrocarbon.
Examiners report
[N/A]
25d.
0.150 g sample of menthol, when vaporized, had a volume of 0.0337 dm 3 at 150 °C and 100.2 kPa. Calculate its molar mass
showing your working.
[2 marks]
Markscheme
«temperature =» 423 K
OR
M=
mRT
pV
«M =
0.150 g× 8.31 J K −1 mol−1× 423 K
100.2 kPa× 0.0337 dm3
=» 156 «g mol –1»
Award [1] for correct answer with no working shown.
Accept “pV = nRT AND n =
m
”
M
for M1.
Examiners report
[N/A]
25e. Determine the molecular formula of menthol using your answers from parts (d)(i) and (ii).
[1 mark]
Markscheme
C10H20O
[1 Mark]
Examiners report
[N/A]
Nitric oxide reacts with chlorine.
2NO (g) + Cl2 (g) → 2NOCl (g)
The following experimental data were obtained at 101.3 kPa and 263 K.
25f.
Deduce the order of reaction with respect to Cl 2 and NO.
[2 marks]
Markscheme
Cl2: first
NO: second
Examiners report
[N/A]
25g.
State the rate expression for the reaction.
[1 mark]
Markscheme
rate = k [NO]2 [Cl2]
Examiners report
[N/A]
25h. Calculate the value of the rate constant at 263 K.
Markscheme
180 / 1.80 x 10 2 «dm6 mol –2 min –1»
Examiners report
[N/A]
[1 mark]
Vanadium has a number of different oxidation states.
26a.
Determine the oxidation state of vanadium in each of the following species.
[2 marks]
Markscheme
V2O5 : + 5
V O2+ : + 4
Do not penalize incorrect notation twice.
[2 marks]
Examiners report
[N/A]
Electrode potentials for the reactions of vanadium and other species are shown below.
26b.
Identify, from the table, a non-vanadium species that can reduce VO 2+ (aq) to V3+ (aq) but no further.
[1 mark]
Markscheme
H2SO3(aq)
OR
Pb(s)
[1 mark]
Examiners report
[N/A]
26c.
2+
Identify, from the table, a non-vanadium species that could convert VO+
2 (aq) to V (aq).
[1 mark]
Markscheme
Zn(s)
[1 mark]
Examiners report
[N/A]
26d.
Formulate an equation for the reaction between VO 2+ (aq) and V2+ (aq) in acidic solution to form V 3+ (aq).
Markscheme
VO2+ (aq) + V2+ (aq) + 2H+ (aq) → 2V3+ (aq) + H2O(l)
Accept equilibrium sign.
[1 mark]
Examiners report
[N/A]
[1 mark]
26e.
Comment on the spontaneity of this reaction by calculating a value for ΔG θ using the data given in (b) and in section 1 of the data
[3 marks]
booklet.
Markscheme
E θ ≪= +0.34 V − (−0.26 V) ≫= +0.60 ≪ V ≫
ΔG θ =≪ −nFE θ = −9.65 × 104 C mol− 1 × 0.60 J C − 1 =≫ −57 900 ≪ J mol− 1 ≫ / − 57.9 ≪ kJ mol− 1 ≫
spontaneous as ΔG θ is negative
Do not award M3 as a stand-alone answer.
Accept “spontaneous” for M3 if answer given for M2 is negative.
Accept “spontaneous as E θ is positive” for M3.
[3 marks]
Examiners report
[N/A]
Sodium chloride, NaCl, can be spread on icy roads to lower the freezing point of water.
The diagram shows the effects of temperature and percentage by mass of NaCl on the composition of a mixture of NaCl and H 2O.
27a. Estimate the lowest freezing point of water that can be reached by adding sodium chloride.
[1 mark]
Markscheme
–21 «ºC»
Examiners report
[N/A]
27b.
Estimate the percentage by mass of NaCl dissolved in a saturated sodium chloride solution at +10 ºC.
[1 mark]
Markscheme
28 «%»
Accept any specific answer in the range 27 to 29 «%».
Examiners report
[N/A]
27c.
Calculate the percentage of water by mass in the NaCl•2H2O crystals. Use the data from section 6 of the data booklet and give
your answer to two decimal places.
Markscheme
M r = 94.48
«2
(1.01 ×2+16.00)
94.48
× 100 =» 38.15 «%»
Award M2 only if answer is to 2 decimal places.
Award [2] for correct final answer.
Award [1 max] for 38.10 %.
Examiners report
[N/A]
[2 marks]
27d.
Suggest a concern about spreading sodium chloride on roads.
[1 mark]
Markscheme
rust/corrosion «of cars and bridges»
OR
waste of important raw material
OR
soil/water salination/pollution «from run off»
OR
erosion of/damage to the road surface
OR
specific example of damage to the ecosystem
OR
«outdoor» temperatures may go below effective levels for NaCl «to lower freezing point» so NaCl could be wasted
OR
roads can refreeze causing hazards
Do not accept “tyre damage”.
Do not accept “economic issues” OR “environmental issues” unless specified (eg accept “increase in costs for local councils road
budgets” but not “cost” alone).
Do not accept “makes roads more slippery”.
Examiners report
[N/A]
Consider the following lipid and carbohydrate.
28a.
Determine the empirical formula of linoleic acid.
Markscheme
C9H16O
[1 mark]
Examiners report
[N/A]
28b.
The empirical formula of fructose is CH 2O. Suggest why linoleic acid releases more energy per gram than fructose.
[1 mark]
Markscheme
ratio of oxygen to carbon in linoleic acid lower
OR
linoleic acid less oxidized
OR
linoleic acid more reduced
Accept “«average» oxidation state of carbon in linoleic acid is lower”.
Examiners report
[N/A]
In order to determine the number of carbon-carbon double bonds in a molecule of linoleic acid, 1.24 g of the lipid were dissolved in 10.0
cm 3 of non-polar solvent.
The solution was titrated with a 0.300 mol dm –3 solution of iodine, I 2.
28c.
State the type of reaction occurring during the titration.
Markscheme
«electrophilic» addition/AE
OR
oxidation–reduction/redox
Examiners report
[N/A]
[1 mark]
28d.
Calculate the volume of iodine solution used to reach the end-point.
[3 marks]
Markscheme
«
1.24 g
280.50 g mo l−1
=» 0.00442 «mol»
0.00884 mol of C=C
OR
ratio of linoleic acid : iodine = 1:2
«volume of I 2 solution =
0.00884 mol
0.300 mol dm−3
=» 0.0295 «dm 3» / 29.5 «cm3»
Award [3] for correct final answer.
Examiners report
[N/A]
28e.
Outline the importance of linoleic acid for human health.
[2 marks]
Markscheme
Any two of:
increases «ratio of» HDL «to LDL» cholesterol
OR
decreases LDL cholesterol «level»
removes plaque from/unblocks arteries
OR
decreases risk of heart disease
decreases risk of stroke «in the brain»
Accept "essential fatty acid".
Do not accept “bad cholesterol” for “LDL cholesterol” OR “good cholesterol” for “HDL cholesterol”.
Do not accept general answers such as “source of energy” OR “forms triglycerides” OR “regulates permeability of cell membranes” etc.
[Max 2 Marks]
Examiners report
[N/A]
A class was determining the concentration of aqueous sodium hydroxide by titrating it with hydrochloric acid, whilst monitoring the pH of
the solution. The sodium hydroxide solution was added into a glass beaker from a measuring cylinder and the hydrochloric acid added
using a burette. One group of students accidentally used a temperature probe rather than a pH probe. Their results are given below.
Volume of aqueous NaOH = 25.0 ± 0.5 cm 3
Concentration of HCl = 1.00 ± 0.01 mol dm−3
−3
−3
29. State and explain how the graph would differ if 1 mol dm sulfuric acid had been used instead of 1 mol dm hydrochloric acid.
[2 marks]
Markscheme
graph would peak/maximum at 17.5 cm 3
OR
smaller volume of acid «needed to reach equivalence»
sulfuric acid is dibasic/diprotic
higher temperature would be reached
Accept “gradient/slope «of graph» is greater/steeper” for M1.
Accept “one mole of sulfuric acid neutralizes two moles of NaOH” for M2.
[2 marks]
Examiners report
[N/A]
Disposable plastic lighters contain butane gas. In order to determine the molar mass of butane, the gas can be collected over water as
illustrated below:
30a.
List the data the student would need to collect in this experiment.
[4 marks]
Markscheme
mass/m of lighter before AND after the experiment
volume of gas/Vgas «collected in the cylinder»
«ambient» pressure/P «of the room»
temperature/T
Accept “change in mass of lighter”.
Accept “weight” for “mass”.
Do not accept just “mass of lighter/gas”.
Accept “volume of water displaced”.
Do not accept “amount” for “volume” or “mass”.
[4 marks]
Examiners report
[N/A]
30b.
Explain why this experiment might give a low result for the molar mass of butane.
[2 marks]
Markscheme
Any two of:
pressure of gas not equalized with atmospheric/room pressure
too large a recorded volume «of gas produces a lower value for molar mass of butane»
OR
cylinder tilted
difficult to dry lighter «after experiment»
OR
higher mass of lighter due to moisture
OR
smaller change in mass but same volume «produces lower value for molar mass of butane»
using degrees Celcius/°C instead of Kelvin/K for temperature
Accept “vapour pressure of water not accounted for” OR “incorrect vapour pressure of water used” OR “air bubbles trapped in cylinder”.
Do not accept “gas/bubbles escaping «the cylinder»” or other results leading to a larger molar mass.
Accept “lighter might contain mixture of propane and butane”.
Do not accept only “human errors” OR “faulty equipment” (without a clear explanation given for each) or “mistakes in calculations”.
[2 marks]
Examiners report
[N/A]
30c.
Suggest one improvement to the investigation.
Markscheme
record vapour pressure of water «at that temperature»
OR
equalize pressure of gas in cylinder with atmospheric/room pressure
OR
tap cylinder before experiment «to dislodge trapped air»
OR
collect gas using a «gas» syringe/eudiometer/narrower/more precise graduated tube
OR
collect gas through tubing «so lighter does not get wet»
OR
dry lighter «before and after experiment»
OR
hold «measuring» cylinder vertical
OR
commence experiment with cylinder filled with water
Accept “adjust cylinder «up or down» to ensure water level inside cylinder matches level outside”.
Accept “repeat experiment/readings «to eliminate random errors»”.
Accept “use pure butane gas”.
[1 mark]
[1 mark]
Examiners report
[N/A]
Analysis of amino acid and protein concentration is a key area of biological research.
The titration curve of aqueous glycine zwitterions with aqueous sodium hydroxide is shown from pH 6.0 to 13.0. Refer to section 33 of
the data booklet.
31a.
Deduce the pH range in which glycine is an effective buffer in basic solution.
Markscheme
«pH range» 8.6–10.6
Accept any value between 8.2 and 11.0.
[1 mark]
Examiners report
[N/A]
[1 mark]
31b.
Enzymes are biological catalysts.
[1 mark]
The data shows the effect of substrate concentration, [S], on the rate, v, of an enzyme-catalysed reaction.
Determine the value of the Michaelis constant (Km) from the data. A graph is not required.
Markscheme
«Km =» 0.67 «mmol dm–3»
Do not penalize if a graph is drawn to determine the value.
[1 mark]
Examiners report
[N/A]
31c.
Outline the action of a non-competitive inhibitor on the enzyme-catalysed reaction.
[2 marks]
Markscheme
does not compete for active site
OR
binds to allosteric site/away from «enzyme» active site
OR
alters shape of enzyme
reduces rate/Vmax
[2 marks]
Examiners report
[N/A]
31d. The sequence of nitrogenous bases in DNA determines hereditary characteristics.
Calculate the mole percentages of cytosine, guanine and thymine in a double helical DNA structure if it contains 17% adenine by
mole.
Markscheme
«% cytosine + % guanine = 100% – 17% – 17% = 66%»
Cytosine: 33 «%» AND Guanine: 33 «%»
Thymine: 17 «%»
[2 marks]
[2 marks]
Examiners report
[N/A]
© International Baccalaureate Organization 2018
International Baccalaureate® - Baccalauréat International® - Bachillerato Internacional®
Printed for Katoh Gakuen Gyoshu High School
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