Mr. Robert Zammit M.Sc.

Unit 10.2 – Sulfur & its compounds - Lesson 1 of 2 Page 1 of 4

Unit 10.2:

Sulfur & its compounds Lesson 2 of 2

Sulfuric Acid

• Sulfuric acid is highly corrosive but is also a very important substance. It is used to make fertilisers, paints, pigments, dyes, detergents and artificial fibres amongst other products. Sulfuric acid is also the acid used in car batteries.

• While dilute sulfuric acid is a normal diprotic acid, concentrated sulfuric acid acts differently. Concentrated sulfuric acid is:

Hygroscopic. If left exposed to air, it absorbs moisture and the volume of the liquid can be seen to increase. As a result, sulfuric acid is used as a drying agent in the laboratory preparation of pure, dry chlorine, hydrogen chloride and sulfur dioxide.

A dehydrating agent, which means that it can take away the elements of

water from a number of substances. These include hydrated salts and sugar. With sugar a black mass of carbon is left.

CuSO4∙5H2O(aq) conc. H2SO4 → CuSO4(aq) + 5H2O(l)

C6H12O6(s) conc. H2SO4 → 6C(s) + 6H2O(l)

A strong oxidizing agent, getting itself reduced to sulfur dioxide in the

process. It can, for example, oxidize copper: 2H2SO4(l) + Cu(s) → CuSO4(s) + SO2(g) + 2H2O(l)

A very strong acid such that it can be used to prepare other acids. For

example, its action on chlorides: H2SO4(l) + NaCl(s) → NaHSO4(s) + HCl(g)

https://www.youtube.com/watch?v=aamm2EHCpBIhttps://www.youtube.com/watch?v=DhCHECcvKOAhttps://www.youtube.com/watch?v=bJBPhpqQxs8https://www.youtube.com/watch?v=aamm2EHCpBIhttps://www.youtube.com/watch?v=DhCHECcvKOAhttps://www.youtube.com/watch?v=bJBPhpqQxs8

Mr. Robert Zammit M.Sc.

Unit 10.2 – Sulfur & its compounds - Lesson 1 of 2 Page 2 of 4

The Contact Process – Industrial Manufacture of Sulfuric acid.

• Sulfuric acid is produced in the Contact process which is composed of

four main steps: 1. Sulfur is burnt in a good supply of air.

S(s) + O2(g) → SO2(g)

2. Sulfur dioxide with more oxygen is heated to high temperatures and passed over a vanadium(V) oxide (V2O5) catalyst. This is done at a temperature of 400-450°C and a pressure of 2atm.

2SO2(g) + O2(g) ⇌ 2SO3(g)

3. If sulfur trioxide is added directly to water, sulfuric acid will be produced. However the reaction gives a large amount of energy, is difficult to control and results in the sulfuric acid evaporating. Instead, sulfur trioxide is added to the recently prepared concentrated sulfuric acid to produce oleum.

SO3(g) + H2SO4(l) → H2S2O7(l)

4. Oleum can be added to the correct amount of water to produce sulfuric acid of the needed concentration.

H2S2O7(l) + H2O(l) → 2H2SO4(l)

By the end of this lesson you should be able to:

Recall and describe the stages in the manufacture of sulfuric acid; recall the actual operating conditions used in the Contact process.

Distinguish between the reactions of sulfuric acid as a dilute acid and as a concentrated acid. Describe and explain specific examples to show concentrated sulfuric acid to be hygroscopic, an

oxidising agent and a dehydrating agent. Recall some uses of sulfuric acid to illustrate its importance in industry and in everyday life.

https://www.youtube.com/watch?v=xjLUJ-7m5v8https://www.youtube.com/watch?v=xjLUJ-7m5v8

Mr. Robert Zammit M.Sc.

Unit 10.2 – Sulfur & its compounds - Lesson 1 of 2 Page 3 of 4

Exercise 2:

1. Fill in the blanks using words from below. Each item can be used once, more than once or not at all.

2 450 600 Vanadium (V) oxide Hydrogen

200 Sulfur trioxide Allotropes Oxygen Water

Rhombic Monoclinic Iron Fertilisers Sulfur dioxide

Sulfur has two ___(a)___ with the most common one being yellow, ___(b)___ sulfur. The other allotrope is ___(c)___ sulfur, which exists as amber needle like crystals. In the first stage of the Contact process, sulfur is burned in air to form ___(d)___ . This gas is then used in the second stage of the process. It is mixed with ___(e)___ gas, then passed over the catalyst ___(f)___ at a temperature of ___(g)___ ºC and ___(h)___ atmospheres pressure. The product of this reaction is ___(i)___ gas. Finally, this gas is absorbed in concentrated sulfuric acid forming a liquid called ‘oleum’ to which the correct amount of ___(j)___ is added in order to obtain ordinary concentrated sulfuric acid. One use of sulfuric acid is to make ___(k)___ .

2. Write balanced chemical equations for all the steps involved in the Contact process.

3. These are some reactions of sulfuric acid: Reaction 1. A + sulfuric acid → copper(II) sulfate + water Reaction 2. B + sulfuric acid → copper(II) sulfate + water + sulfur dioxide Reaction 3. C + sulfuric acid → sodium sulfate + water + carbon dioxide Reaction 4. D + sulfuric acid → sodium hydrogensulfate + hydrogen chloride Reaction 5. E + sulfuric acid → carbon + water + dil. sulfuric acid a. Name the reagents A to E. b. State whether sulfuric acid has to dilute or concentrated in reactions 1 to 5. c. What is the role of sulfuric acid in reaction 2? d. What is the role of sulfuric acid in reaction 5? e. Write balanced chemical reactions for equations 1 to 5.

4. Sulfuric acid is a strong oxidizing agent. It can oxidize bromide ions to bromine and iodide ions to iodine. However, sulfuric acid cannot oxidize chloride ions to chlorine. Explain why this is so.

Mr. Robert Zammit M.Sc.

Unit 10.2 – Sulfur & its compounds - Lesson 1 of 2 Page 4 of 4

Model Answers to Exercise 2:

1) Question 1

a) allotropes b) rhombic c) monoclinic d) sulfur dioxide e) oxygen f) vanadium(V) oxide g) 450oC h) 2 atmospheres (atm) i) sulfur trioxide j) water k) fertilisers

2) Question 2 a) Step 1: S(s) + O2(g) → SO2(g) b) Step 2: 2SO2(g) + O2(g) ⇌ 2SO3(g) c) Step 3: SO3(g) + H2SO4(l) → H2S2O7(l) d) Step 4: H2S2O7(l) + H2O(l) → 2H2SO4(l)

3) Question 3 a) A: copper(II) oxide (or copper(II) hydroxide); B: copper; C: sodium carbonate (or sodium

hydrogen carbonate); D: sodium chloride; E: glucose b) 1: dilute; 2: concentrated; 3: dilute; 4: concentrated; 5: concentrated c) Oxidising agent (it oxidises Cu to Cu2+). d) Dehydrating agent (removes water causing a chemical change). e) Reaction 1: CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l)

Or: Cu(OH)2(s) + H2SO4(aq) → CuSO4(aq) + 2H2O(l) Reaction 2: Cu(s) + 2H2SO4(l) → CuSO4(s) + SO2(g) + 2H2O(l) Reaction 3: Na2CO3(s) + H2SO4(aq) → Na2SO4(aq) + H2O(l) + CO2(g) Or: 2NaHCO3(s) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) + 2CO2(g) Reaction 4: NaCl(s) + H2SO4(l) → NaHSO4(s) + HCl(g) Reaction 5: C6H12O6(s) conc. H2SO4 → 6C(s) + 6H2O(l)

4) Question 4 Sulfuric acid is a stronger oxidising agent than Bromine and Iodine, BUT NOT chlorine. The latter is a stronger oxidising agent than sulfuric acid.

Sulfuric AcidThe Contact Process – Industrial Manufacture of Sulfuric acid.By the end of this lesson you should be able to:Exercise 2:Model Answers to Exercise 2: