Chapter 21 (41 marks)

Question 2 (03 Chem1)

Part of the Contact Process for the manufacture of sulfuric acid involves the conversion of sulfur dioxide to sulfur trioxide, as shown by the equation

2SO2(g) + O2(g) ⇌ 2SO3(g) ΔH = –192 kJ mol–1

As part of a laboratory study of this process, a container was filled with an equilibrium mixture of sulfur dioxide, sulfur trioxide and oxygen in the presence of a catalyst. The container was initially at 450oC. The container had a fixed volume and was thermally well insulated.

Concentrations during a following experiment are shown on the diagram below.

a. What change occurred at the 10 minute point?1 mark

b. Which components of the equilibrium mixture are represented by X and Y? 1 mark

c. Give explanations for the changes in concentration that occur in X, Y and O2between 10 and 20 minutes. 3 marks

d. Would the temperature of the mixture increase, decrease or remain the same between 10 and 20 minutes? Explain your reasoning. 2 marks

Question 5 (04 Chem1)

The industrial production of sulfuric acid can be described as a four-stage process beginning with the burning of raw sulfur with oxygen.

a. Stage 1 The burning of sulfur

Give the equation for the burning of sulfur in oxygen.1 mark

b. Stage 2 The oxidation of sulfur from the +4 to the +6 oxidation state

i. Give the equation for this reaction.1 mark

ii. What goes wrong in the industrial process if the temperature for this stage of the process is too high, and why? 2 marks

iii. What goes wrong in the industrial process if the temperature for this stage of the process is too low, and why? 1 mark

c. Stage 3 The conversion of S in the +6 oxidation state from a gaseous to a liquid form by reacting the +6 form of the gas with a suitable solvent

i. Give the chemical reaction for this process.1 mark

ii. Explain why water is not used as the solvent for this process.1 mark

d. Stage 4 The production of liquid sulfuric acid

Give the chemical reaction for this process.1 mark

Question 5 (05 Chem1)

Sulfuric acid can be produced from mined sulfur via the Contact Process. The Þ rst two stages in the industrial

production of sulfuric acid by this process are represented below.

a. Give a reason why, in stage I, the molten sulfur is sprayed into the burner rather than being allowed to flow through it. 1 mark

b. A conflict is involved in choosing the best temperature to be used in stage II, where the reaction is

2SO2(g) + O2(g) ⇌ 2SO3(g)

i. Describe the nature of the conflict and explain how the conflict is resolved.2 marks

ii. Would increasing the pressure of the reacting mixture in the converter affect the amount of SO3

produced in stage II? Explain your answer.2 marks

c. Sulfuric acid is a diprotic acid. The Þ rst ionisation reaction of sulfuric acid is complete while its secondionisation is that of a weak acid. Give chemical equations for both the first and second ionisation reactionsof sulfuric acid. 2 marks

d. Give one major industrial use of sulfuric acid.1 mark

Question 8 (06 Chem1)

One of the steps involved in the industrial preparation of sulfuric acid is the oxidation of sulfur dioxide to sulphur trioxide according to the equation

2SO2(g) + O2(g) ⇌ 2SO3(g)

a. Give the name or formula for the catalyst that is most widely used for this reaction.1 mark

b. The graph below shows the percentage conversion of sulfur dioxide to sulfur trioxide at equilibrium at1 atm pressure and various temperatures.

There is almost complete conversion of sulfur dioxide to sulfur trioxide at 300°C. However, this reactionis performed at a higher temperature of approximately 450°C in industry. Why? 1 mark

c. Explain why

i. high pressures would increase the equilibrium yield of sulfur trioxide in this reaction.1 mark

ii. atmospheric pressure is usually used in industry, even though high pressures increase the equilibriumyield of sulfur trioxide in this reaction. 1 mark

d. A chemical reaction that involves sulfuric acid occurs in each of the following situations. Write a balancedchemical equation for each reaction, showing the states of all reactants and products.

i. Dilute sulfuric acid is added to sodium carbonate solution.2 marks

ii. Sulfur trioxide gas is bubbled through concentrated sulfuric acid.1 mark

iii. A piece of zinc metal is added to 6 M sulfuric acid. Zinc ions are formed as well as an oxide of sulphur in which sulfur exhibits an oxidation state of +4. 2 marks

Question 4 (07 Chem1)

Sulfur dioxide (SO2) is a chemical of major industrial significance.

a. SO2 gas can be produced in a reaction between concentrated sulfuric acid and nickel metal. A solutioncontaining Ni2+ ions is also formed.

Write balanced equations for the

i. oxidation reaction1 mark

ii. reduction reaction1 mark

iii. overall reaction, showing the states of all reactants and products.2 marks

b. SO2 can also be produced in a chemical reaction between zinc sulfate (ZnSO3) and hydrochloric acidaccording to the equation

ZnSO3(s) + 2H+(aq) → Zn2+(aq) + SO2(g) + H2O(l)

Is this reaction also a redox reaction? Explain your answer.1 mark

c. The SO2 produced as a by-product of the extraction of lead from its ore can cause serious pollution. Inorder to avoid releasing the SO2 into the atmosphere it is often collected and used to produce chemicalsof industrial importance. Give the formula of such a chemical. 1 mark

d. The following pairs of statements refer to the reaction of SO2(g) with O2(g) in the presence of

vanadium (V) oxide. Each statement contains one or more missing words.Circle the most appropriate words beside each statement.

i.

Statements / Circle the most appropriate words
1. The product of this reaction is______. / oleum sulphuric acid sulfur trioxide
2. At constant temperature, the chemical energy of the product is ______the chemical energy of the reactants. / equal to more than less than

1 mark

ii.

1. The equilibrium yield of product is
______as temperature
decreases at constant pressure. / Unchanged increased decreased
2. The equilibrium yield of product is
______as pressure increases
at constant temperature. / Unchanged increased decreased

1 mark

iii.

1. The reaction rate is ______as
the temperature increases at constant
pressure. / Unchanged increased decreased
2. The activation energy of the reaction
is ______by the presence of
vanadium (V) oxide. / Unchanged increased decreased

1 mark