The Industrial Manufacture of Chemicals

Question 1

What is produced in the contact process?

Answer 1

• Sulphuric acid

Question 2

What are the uses of sulphuric acid?

Answer 2

1. Most used industrial acid
2. Lead acid batteries
3. Refining ore
4. Waste water purification
5. Fertiliser
6. Detergent
7. Paint

Question 3

How is sulphuric acid used in the manufacture of detergents?

Answer 3

Used to make sulphonate products

Question 4

How is sulphuric acid used in the manufacture of fertiliser?

Answer 4

Reacted to make:

1. Phosphates soluble to plants
2. Ammonia easier to handle

Question 5

How is sulphuric acid used in the manufacture of paint?

Answer 5

Reacted with titanium ore to make a main pigment in paint

Question 6

What are the four steps of the Contact Process?

Answer 6

1. Make sulphur dioxide
2. Convert sulphur dioxide to sulphur trioxide
3. Dissolve sulfur trioxide in concentrated sulfuric acid to form liquid oleum
4. Oleum is diluted with measured amounts of water to form concentrated sulfuric acid

Question 7

What are the two methods of making sulphur dioxide?

Answer 7

1. Burn sulphur in an excess of air
   S (s) + O₂ (g) → SO₂ (g)
2. Heat sulphides in an excess of air
   4FeS₂ (s) + 11O₂ (g) → 2Fe₂O₃ (s) + 8SO₂ (g)

Question 8

What is the equation for making sulphur trioxide?

What are the required conditions?

Answer 8

2SO₂ (g) + O₂ ⇌ 2SO₃
ΔH = -ve

Catalyst: Vanadium (V) oxide, V₂O₅
Temperature: 400-450 ˚C
Pressure: 1-2 atm

Question 9

Why is a temperature of about 450˚C used in the making of sulphur trioxide?

Answer 9

It is a compromise between percentage yield of sulphur trioxide and rate of reaction

Question 10

Why is a low pressure used in the making of sulphur trioxide?

Answer 10

Lowers the cost of production

Question 11

Why isn’t sulphuric acid made by dissolving sulphur trioxide in water?

Answer 11

The reaction produces fumes which:

1. Are dangerous
2. Reduce the yield of acid obtained

Question 12

How is sulphuric acid made from sulphur trioxide?

Answer 12

1. Dissolve SO₃ in sulphuric acid to form oleum
   SO₃ (g) + H₂SO₄ (l) → H₂S₂O₇ (l)
2. Dissolve oleum in water
   H₂S₂O₇ (l) + H₂O (l) → 2H₂SO₄ (l)

Question 13

What is produced from the Haber process?

Answer 13

Ammonia

Question 14

What is the main use of ammonia?

Answer 14

Fertilisers for crops - used for the food production for half the world’s population

Question 15

Give reasons why it is important for farmers to use fertilisers on their land

Answer 15

1. Provides essential plant nutrients
2. Increases the yield of crops
3. Replaces nutrients removed by growing plants

Question 16

What is the equation for the Haber process? Is it exothermic or endothermic?

Answer 16

N2 (g) + 3H₂ (g) ⇌ 2NH₃ (g)

Exothermic

Question 17

What raw materials are used to supply the hydrogen and nitrogen for the Haber process?

Answer 17

• Hydrogen*: from natural gas or cracking hydrocarbons

* Nitrogen*: air

Question 18

How are the unreacted gases separated from the ammonia formed?

Answer 18

The reaction mixture is cooled until ammonia liquefies and can be removed

Question 19

What happens to any unreacted reactants in the Haber process?

Answer 19

They are recycled. Continual recycling leads to an overall conversion rate of about 98%

Question 20

Looking at the equation, describe and explain conditions in temperature and pressure which would favour a high yield of ammonia:

N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)
ΔH = -91 kJ/mol

Answer 20

• Temperature*: low - forwards reaction releases heat to oppose the low temperature
• Pressure*: high - fewer moles on RHS

Question 21

What are the actual conditions used for the Haber process?

Answer 21

• Temperature*: 400-450 ˚C
• Pressure*: 200 atm
• Catalyst*: iron catalyst

Question 22

Why are the compromise conditions for temperature and pressure in the Haber process used?

Answer 22

Temperature: higher temperatures lead to a faster rate of reaction despite lower % yield of ammonia

• Pressure*
• high building costs - equipment has to be strong to withstand the pressure
• using high pressures increases the running costs of the plant
• safety aspects

Question 23

When using HCl, what is the main danger? How can this be mitigated when using it in experiments?

Answer 23

It is corrosive and can cause burns

1. Wear safety gloves
2. Wear eye protection
3. Place bung in the end of the tube