G10 IB Bridging Year Chemistry
Topic 6.1 Acids and bases
Assignment (3)
Name: _____________________________
Concentrations of Solutions
1. Which sample contains the greatest number of ions?
2.
A.
25 cm3 of 0.40 mol dm-3 NaCl
B.
50 cm3 of 0.20 mol dm-3 MgCl2
C.
100 cm3 of 0.10 mol dm-3 KNO3
D.
200 cm3 of 0.05 mol dm-3 CuSO4
What amount of solute ions, in moles, is present in 50cm3 of 0.10 mol dm-3 sodium hydroxide solution?
A. 2.5 x 10-3
B. 5.0 x 10-3
C. 1.0 x 10-2
D. 5.0 x 10-2
3.
A 4.00 g sample of sodium hydroxide, NaOH, is dissolved in water and made up to 500cm3 of aqueous
solution. What is the concentration of the resulting solution?
A. 0.1mol dm-3
B. 0.2mol dm-3
C. 0.5mol dm-3
D. 1.0mol dm-3
4. What volume of 0.500 mol dm-3 sulfuric acid solution is required to react completely with 10.0g of calcium
carbonate according to the equation below?
CaCO3(s) + H2SO4(aq) g CaSO4(aq) + H2O(l) + CO2(g)
A. 100cm3
B. 200cm3
C. 300cm3
D. 400cm3
1
5. 25.0 cm3 of 2.00 mol dm-3 HNO3(aq) reacts completely with 20.0 cm3 of Ba(OH)2(aq). What is the
concentration of barium hydroxide solution?
A.
0.800 mol dm-3
B.
1.25 mol dm--3
C.
2.00 mol dm-3
D.
2.50 mol dm-3
6. 10.0 cm3 of 0.200 moldm-3 H3PO4(aq) is converted into Na2HPO4(aq).
What volume (in cm3) of 0.200 moldm-3 NaOH(aq) is required?
A.
10.0
B.
13.3
C.
20.0
D.
30.0
7. Powdered zinc reacts with Cu2+ ions according to the equation below:
Zn(s) + Cu2+(aq)
Zn2+ (aq) + Cu(s)
g
What will be the result of adding 3.25 g of Zn to 100 cm3 of 0.25 mol dm-3 CuSO4 solution?
A.
All the Cu2+ ions react and some solid zinc remains.
B.
All the Cu2+ ions react and no solid zinc remains.
C.
All the solid zinc reacts and Cu2+ ions remain.
D.
Neither solid zinc nor Cu2+ ions remain.
2
8. When excess BaCl2(aq) was added to a sample of Fe(NH4)2(SO4)2(aq) to determine the amount in moles
of sulfate present, 5.02 x 10-3 mol of BaSO4 was obtained.
How many moles of sulfate ions and iron ions were in the sample of Fe(NH4)2(SO4)2?
9.
A.
Amount of sulfate ions/
moles
5.02 x 10-3
Amount of iron ions/
moles
2.51 x 10-3
B.
10.04 x 10-3
5.02 x 10-3
C.
2.51 x 10-3
5.02 x 10-3
D.
10.04 x 10-3
2.51 x 10-3
Consider the following reaction:
CaCl2(aq) + 2AgNO3(aq) g 2AgCl(s) + Ca(NO3)2(aq)
2.0 dm3 of 0.50 moldm-3 CaCl2(aq) is mixed with 1.0 dm3of 2.0 mol dm-3 AgNO3(aq).
What are the concentrations of Ca2+(aq) and NO3-(aq) after mixing?
[Ca2+]/moldm-3
[NO3-]/mol dm-3
A.
0.66
0.33
B.
0.33
0.66
C.
1.0
2.0
D.
3.0
1.5
10. Which would be the best method to decrease the random uncertainty of a measurement in an acid-base
titration
A.
Repeat the titration
B.
Ensure your eye is at the same height as the meniscus when reading from the burette
C.
Use a different burette
D.
Use a different indicator for the titration
3
11.
Vinegar is a solution of ethanoic acid. A 10.0 cm3 portion of a certain brand of vinegar needed 55.0 cm3
of 0.200 mol dm-3 sodium hydroxide solution to neutralise the ethanoic acid in it.
g
CH3COOH(aq) + NaOH(aq)
CH3COONa(aq) + H2O(1)
Calculate the concentration of ethanoic acid in the vinegar in mol dm-3.
•
n(NaOH) = 0.200 x 0.0550 = 0.0110 mol
•
Mole ratio of NaOH : CH3COOH = 1:1
o
•
[3]
n(CH3COOH) = 0.0110 mol
Concentration of CH3COOH =
!.!##!
!.!#!!
= 1.10 mol dm-3
12.
A household cleaner contains aqueous ammonia. A 2.447 g sample of the cleaner is diluted with water to
20.00 cm3. This solution requires 28.51 cm3 of 0.4040 mol dm-3 sulfuric acid for complete neutralisation.
(a) Write a balanced chemical equation for the reaction of sulfuric acid with ammonia to form
ammonium sulfate.
•
[1]
NH3 (aq) + H2SO4 (aq) à (NH4)2SO4 (aq)
(b) Calculate the amount (moles) of sulfuric acid required for this reaction, and the amount (in moles),
mass and percentage by mass of ammonia present in the household cleaner.
[4]
• n(H2SO4) = 0.4040 x 0.02851 = 0.01152 mol
• Mole ratio H2SO4 : NH3 = 1:2
o
n(NH3) = 0.01152 x 2
= 0.02304 mol
• Mass of NH3 = 0.02304 x (14.01 + 1.01 x 3)
= 0.3925 g
• Percentage by mass =
!.$%&'
&.(()
× 100%
= 16.04 %
4
13.
The percentage by mass of calcium carbonate in eggshell was determined by adding excess hydrochloric acid
to ensure that all the calcium carbonate had reacted. The excess acid left was then titrated with aqueous
sodium hydroxide.
(a)
A student added 27.20cm3 of 0.200mol dm-3 HCl to 0.188g of eggshell. Calculate the amount, in mol,
of HCl added.
[1]
•
(b)
Number of moles of HCl added = 0.200 x 0.02720
= 0.00544 mol
The excess acid requires 23.80cm3 of 0.100mol dm-3 NaOH for neutralization. Calculate the amount,
in mol, of acid that is in excess.
[1]
•
Number of moles of NaOH titrated = 0.100 x 0.02380
= 0.00238 mol
(Mole ratio of NaOH : HCl = 1:1)
Number of moles of excess HCl (titrated) = 0.00238 mol
(c)
Determine the amount, in mol, of HCl that reacted with the calcium carbonate in the eggshell.
•
(d)
(e)
Number of moles of HCl reacted with the CaCO3 in the eggshell = 0.00544 – 0.00238
= 0.00306 mol
State the equation for the reaction of HCl with the calcium carbonate in the eggshell.
•
!.!!$!*
= 0.00153 mol
&
Calculate the mass and the percentage by mass of calcium carbonate in the eggshell sample.
•
Mass of CaCO3 in the sample = 0.00153 x (40.08 + 12.01 + 16.00 x 3)
= 0.153 g
•
Percentage by mass =
•
[1]
Mole ratio of HCl reacted : CaCO3 = 2:1
Number of moles of CaCO3 =
(f)
[2]
CaCO3 (s) + 2 HCl (aq) à CaCl2 (aq) + H2O (l) + CO2 (g)
Determine the amount, in mol of calcium carbonate in the sample of the eggshell.
•
[1]
!.#'$
x 100%
!.#++
= 81.5 %
5
[3]
(g)
Deduce one assumption mass in arriving at the percentage of calcium carbonate in the eggshell
sample.
•
[1]
CaCO3 is the only substance in the egg shell that reacts with acid/ impurities in the egg shell do
not react with acid/ no other carbonates in the egg shell
6