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Calculations revision qs
Part 1
Date:
Time: 1 hour 2 minutes
Total marks available: 60
Total marks achieved: ______
Q1. A student used the apparatus in the diagram to determine the molar volume of a gas.
The student used a piece of magnesium ribbon, which was about 5 cm in length, and the dilute hydrochloric
acid was in excess. The experiment was repeated three times at 24°C and the following results were
obtained.
The equation for the reaction is
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
(a) (i) Calculate the number of moles of magnesium used by the student in each experiment.
(1)
(ii) Use your answer from part (a)(i)
produced.
to deduce the number of moles of hydrogen gas that should be
(1)
(iii) Calculate, using the Ideal Gas Equation, the volume of hydrogen gas, in cm3, that should be
produced in each of these experiments.
[pV = nRT R = 8.31 J mol−1 K−1 p = 101 000 Pa]
(4)
(b) Give a reason why the student repeated the experiment three times.
(1)
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(c) Give three reasons for the difference between your calculated value in (a)(iii) and the actual volumes
of hydrogen gas obtained by the student.
For each reason, identify a change to either the apparatus or the chemicals that could be made by the
student to improve the result.
(6)
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(Total for question = 13 marks)
Q2.
Brand X is unlike many conventional toilet cleaners in that it does not contain bleach, but instead contains
hydrochloric acid. The label states that the toilet cleaner contains 9 g of HCl per 100 cm3 of the toilet
cleaner.
An industrial technician was given the task of checking the validity of this statement. Using 25.0 cm3
portions of the toilet cleaner, the technician carried out a titration using 2.50 mol dm−3 sodium hydroxide
solution and obtained the following results.
(a) (i) Complete the table and calculate the mean titre by selecting the appropriate results.
(1)
(ii) Write the equation for the titration reaction. State symbols are not required.
(1)
(iii) Calculate the number of moles of sodium hydroxide that reacted.
(1)
(iv) Hence state the number of moles of hydrochloric acid that reacted with the sodium hydroxide.
(1)
(v) Calculate the mass of HCl present in 100 cm3 of the toilet cleaner. Give your answer to 3 significant
figures.
(2)
(vi) Using the technician's results, comment on the validity of the manufacturer's statement that the
toilet cleaner contained 9 g of HCl per 100 cm3. Justify your answer.
(1)
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(vii) Explain why titrations involving the use of a 2.50 mol dm−3 sodium hydroxide solution would not be
advisable in a school or college laboratory.
(1)
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(b) Conventional toilet cleaners contain a bleaching agent. Chloric(I) acid, HOCl, is one such substance.
Draw the dot and cross diagram for chloric(I) acid. Show outer electrons only.
(1)
(c) The instructions for the use of Brand X state that the toilet cleaner should not be used with bleaching
agents.
Complete the equation for the reaction between the hydrochloric acid in the toilet cleaner and the
chloric(I) acid in the bleaching agent. Give a reason why this reaction is to be avoided in accordance with
the instructions for the use of the toilet cleaner.
(2)
Equation
HCl
+
HOCl
→
Reason
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(d) Another bleaching agent is sodium chlorate(I), NaClO, which can be purchased as a solution. It can
also be obtained by bubbling chlorine gas into sodium hydroxide solution.
(i) Give the oxidation numbers of the chlorine-containing species in the equation below and classify the
reaction as a result of your answer.
(2)
Type of reaction
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(ii) State how the reaction conditions would need to be changed in order to produce sodium chlorate(V)
instead of sodium chlorate(I).
(1)
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(iii) Give the equation for the reaction between chlorine and sodium hydroxide solution that forms
sodium chlorate(V) as one of the products. State symbols are not required.
(2)
(Total for question = 16 marks)
Q3.
What is the number of ions in 9.53 g of magnesium chloride, MgCl2?
[Avogadro constant = 6.02 × 1023 mol–1]
(1)
A
B
6.02 × 1022
1.20 × 1023
C
D
1.81 × 1023
6.02 × 1023
(Total for question = 1 mark)
Q4. Ethanol, C2H5OH, is a member of the homologous series of alcohols.
Calculate the number of molecules in 55.2kg of ethanol.
[Avogadro Constant = 6.02 × 1023 mol–1]
(2)
(Total for question = 2 marks)
Q5. How many molecules are present in 16 g of oxygen gas, O2(g)?
[Avogadro constant = 6 × 1023 mol−1]
A
B
96 × 1023
12 × 1023
C
D
6 × 1023
3 × 1023
(Total for question = 1 mark)
Q6. The properties of elements and their compounds are determined by their structure and bonding.
(i) In a dry container, a fluoride of silver reacts with sulfur to produce disulfur difluoride. Complete the
equation for this reaction. State symbols are not required.
(1)
(ii) Explain, by using the oxidation numbers of all the atoms, whether or not this is a redox reaction.
(3)
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(Total for question = 4 marks)
Q7. Lithium reacts with water to produce hydrogen.
Li(s) + H2O(l) → LiOH(aq) + ½H2(g)
(a) In an experiment, 0.069 g (0.01 mol) of lithium produced 90 cm3 of hydrogen at room temperature and
pressure. What is the percentage yield of hydrogen?
[1 mol of any gas occupies 24 dm3 at room temperature and pressure.]
(1)
A
45%
C
75%
B
60%
D
90%
(b) Which of the following is not a possible reason for the yield being less than 100%?
(1)
A
Some oil remained on the surface of the lithium.
B
Hydrogen gas is very soluble in water.
C
A layer of oxide was present on the surface of the lithium.
D
Some of the hydrogen gas escaped collection.
Q8. 1.40 g of an alkene gave 3.77 g of a dichloroalkane on reaction with chlorine.
What is the molecular formula of the alkene?
A
C2H4
C
C4H8
B
C3H6
D
C6H12
(Total for question = 1 mark)
Q9.
This question is about the reaction between sodium carbonate solution and dilute nitric acid.
Na2CO3(aq) + 2HNO3(aq) → 2NaNO3(aq) + CO2(g) + H2O(l)
(a) What is the ionic equation for this reaction?
(1)
A
Na2CO3(aq)
+
2H+(aq)
→
2Na+(aq)
B
Na+(aq)
+
NO3-(aq)
→
NaNO3(aq)
C
CO32-(aq)
D
CO32-(aq)
+
+
2H+(aq)
2HNO3(aq)
→
→
+
CO2(g)
CO2(g) +
H2O(l)
2 NO3-(aq)
+
+
H2O(l)
CO2(g) + H2O(l)
(b) What is the volume of carbon dioxide produced from the complete reaction of 0.10 mol of nitric acid at
room temperature and pressure?
[1 mol of any gas occupies 24 dm3 at room temperature and pressure.]
(1)
A
1.2 dm
3
3
C
2.4 dm
B
1.8 dm3
D
3.6 dm3
(c) What volume of sodium carbonate solution of concentration 0.500 mol dm−3, would be needed to
completely react with 25.0 cm3 of nitric acid of concentration 0.250 mol dm−3?
(1)
A
6.25 cm3
B
12.50 cm3
C
18.75 cm3
D
25.00 cm3
Q10.
Nickel is an element in the d-block of the Periodic Table.
(a) Complete the electronic configuration of a nickel atom using the s, p, d notation.
(1)
2
1s ....................................................................................................................
(b) A sample of nickel is made up of three isotopes. The percentage abundances are shown in the table
below.
Calculate the relative atomic mass of nickel. Give your answer to two decimal places.
(2)
(c) Nickel reacts with carbon monoxide, CO, to give the compound nickel carbonyl, Ni(CO)4.
Ni(s) + 4CO(g) → Ni(CO)4(g)
(i) Calculate the volume of carbon monoxide, in dm3, measured at room temperature and pressure, that
is required to react completely with 5.87 g of nickel.
[Relative atomic mass: Ni = 58.7
Molar volume of a gas = 24 dm3 mol−1 at room temperature and pressure.]
(3)
(ii) Calculate the number of carbon monoxide molecules present in the volume of gas you have
calculated in (c)(i).
[The Avogadro constant, L = 6.02 × 1023 mol−1]
(1)
(d) Nickel(II) nitrate, Ni(NO3)2, can be made by several different methods.
Method 1
Nickel(II) oxide, NiO, was reacted with dilute nitric acid according to the equation
NiO(s) + 2HNO3(aq) → Ni(NO3)2(aq) + H2O(l)
(i) Calculate the volume of 2.00 mol dm−3 dilute nitric acid, in cm3, that was required to exactly
neutralize 1.494 g of nickel(II) oxide.
Use the relative atomic masses: Ni = 58.7, O = 16.0
(3)
Method 2
A volume of 25.0 cm3 of 2.00 mol dm−3 nitric acid, HNO3, was transferred to a beaker. Solid nickel(II)
carbonate, NiCO3, was added until it was in excess.
(ii) Why was excess nickel(II) carbonate used?
(1)
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(iii) Why must the beaker be much larger than the volume of acid used?
(1)
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(iv) Write a balanced equation for the reaction between nickel(II) carbonate and dilute nitric acid,
including state symbols.
(2)
*(v) For Method 2, describe the practical steps that you would take to obtain pure dry crystals of
hydrated nickel(II) nitrate, Ni(NO3)2.6H2O, from a mixture of nickel(II) nitrate solution and unreacted solid
nickel(II) carbonate.
(4)
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(Total for question = 18 marks)
Q11. A compound has the following percentage composition by mass.
C 61.0%
H 15.3%
N 23.7%
The empirical formula of the compound is
A
CH3N
B
C3H9N
C
C6H9N2
D
C8H2N3
(Total for question = 1 mark)