7.8.1 Sulphur Chemistry

Questions

Section A

For each of the questions only one of the lettered responses (A – D) is correct.

Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet.

1. Which one of the following is not produced in the reaction of sodium iodide with concentrated sulphuric acid?

A Hydrogen sulphide

B Iodine

C Sulphur dioxide

D Sulphur trioxide

2 In the production of sulphuric acid one of the steps involves the conversion of sulphur dioxide to sulphur trioxide.

2SO₂ (g) + O₂ (g) � 2SO₃ (g)

Which one of the following statements is true?

A The forward reaction is favoured by reducing the pressure of the system to two-thirds of

atmospheric pressure.

B Since the forward reaction is endothermic the reaction is carried out at about 450^oC.

C A catalyst of iron is used to speed up the rate of attainment of equilibrium.

$D The rate of formation of sulphur trioxide is twice the rate of disappearance of oxygen.

Section B

Answer all questions in the spaces provided.

1. Describe, with experimental details, how you would prove a colourless solution contained the sulphite ion but not the sulphate ion.

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2. Sodium thiosulphate is white, crystalline compound of formula Na₂S₂O₃.5H₂O.

(a)(i) Describe fully how crystals of sodium thiosulphate may be obtained in the

laboratory.

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(ii) Suggest reasons why this preparation should not be carried out under acidic conditions.

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(b) Thiosulphate ions can behave as reducing agents. Write ionic equations for the

reaction of thiosulphate ions with

(i) Chlorine

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(ii) Iodine

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(c)(i) Does the oxidising power of the halogens increase or decrease with increase in

atomic number?

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(ii) Explain using oxidation numbers, how this trend is shown by the reactions in part

(b).

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3 Sulphuric acid is the chemical industry’s major product, with ammonia in second place.

The conversion of sulphur to sulphuric acid is represented in the scheme below:

sulphur step A sulpur step B sulphur step C 95.8%

dioxide trioxide sulphuric

acid

water step D

air air

98%

sulphuric

acid

storage

(a) Sulpur can be stored as powder in the rhombic form.

(i) Draw the shape of a sulphur molecule in rhombic sulphur.

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(ii) Suggest a reason why the sulphur is melted before combustion.

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(iii) Describe what happens to the sulphur molecules as the temperature rises from room temperature to just below the boiling point.

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(b)(i) Write equations for steps A and B.

step A

step B

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(ii) State the conditions used in step B.

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(iii) Explain how consideration of reaction rate and equilibrium principles contribute to the choice of reaction conditions.

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(iv) In step C, why is sulphur trioxide passed into 98% sulphuric acid rather than water?

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(b) Concentrated sulphuric acid is used in the nitration of benzene.

Using an equation, explain the role which it plays in this process.

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