C6.1 - Improving Processes And Products

Question 1

What are the essential elements for plants to grow?

Answer 1

Nitrogen, phosphorus and potassium. Plants do not grow well if there are limited supply in the soil - may show symptoms of mineral deficiency. Quality and yield of food will also be reduced.

Question 2

What are fertilisers?

Answer 2

Substances that replace the elements used by plants as they grow.

Question 3

What form do fertilisers need to be in to be absorbed by plants?

Answer 3

Fertilisers need to be in a water-soluble form in order to be absorbed by the plant roots.

Question 4

What are the typical symptoms of deficiency when a plant lacks an essential element?

Answer 4

Question 5

What is the Haber process?

Answer 5

The Haber process manufactures ammonia from nitrogen and hydrogen:

Question 6

What are the raw materials for the Haber process?

Answer 6

Air, natural gas, steam

Question 7

How is nitrogen manufactured for the Haber process?

Answer 7

It is manufactured by the fractional distillation of liquefied air (air is 78% nitrogen).

Question 8

How is hydrogen manufactured for the Haber process?

Answer 8

It is manufactured by reacting natural gas (mostly methane) with steam.

Question 9

What are the conditions needed for the Haber process?

Answer 9

Temperature of 450C
200 atm pressure
Iron catalyst

Question 10

What are the steps for the Haber process?

Answer 10

In the Haber process:

1. nitrogen (extracted from the air) and hydrogen (obtained from natural gas) are pumped through pipes.
2. the pressure of the mixture of gases is increased to 200 atmospheres.
3. the pressurised gases are heated to 450 °C and passed through a tank containing an iron catalyst.
4. the reaction mixture is cooled so that ammonia liquefies and can be removed.
5. unreacted nitrogen and hydrogen are recycled (improves yield to around 97%).

Question 11

What factors determine the pressure chosen for the Haber process?

Answer 11

If the pressure is increased, the equilibrium position moves to the right and the yield of ammonia increases as it is the side that has the fewer number of moles. However, it would be hazardous and expensive to choose a very high pressure. The higher equilibrium yield would not justify the additional costs, so a compromise pressure is chosen.

Question 12

What factors determine the temperature chosen for the Haber process?

Answer 12

The backward reaction of the Haber process is endothermic so if the temperature is increased, the equilibrium position moves to the left and the equilibrium yield of ammonia decreases. Hence, a high equilibrium yield is favoured by a low temperature. The temperature chosen is low enough to achieve a reasonable yield, but high enough to achieve a reasonable rate of reaction. Iron catalyst also works more efficiently above 400C.

Question 13

What happens in a fertiliser factory?

Answer 13

A range of compounds are made in a fertiliser factory which will be used to create fertilisers for different needs.

These include:

Question 14

Raw materials and processes in fertiliser manufacture.

Answer 14

Question 15

How do you make potassium sulfate in the lab?

Answer 15

Question 16

How do you make ammonium sulfate in the lab?

Answer 16

Question 17

How are industrial processes different to lab processes?

Answer 17

When you make a substance in the school laboratory, you usually make a small amount at one time, using a batch process. On the other hand, many industrial processes are continuous processes. They make large amounts and go on all the time.

Question 18

Compare batch process to continuous process.

Answer 18

Question 19

What is the difference between how the processes start in the lab vs fertiliser factories?

Answer 19

In the laboratory, you start with pure substances bought from a chemical manufacturer. Fertiliser factories start with raw materials (substances obtained from the ground, air, or sea). These must be purified before use, or the product must be purified at the end.

Question 20

What is the contact process and what are the raw materials required?

Answer 20

The contact process, for making sulfuric acid, is a process which involves a reversible reaction.

The raw materials needed to make sulfuric acid are:

sulfur
air (source of oxygen)
water

Question 21

What is stage 1 of the Contact process?

Answer 21

In stage 1, sulfur burns in air to produce sulfur dioxide.

Question 22

What is stage 2 of the Contact process?

Answer 22

In stage 2 of the contact process, sulfur dioxide and oxygen react together to produce sulfur trioxide.

Question 23

What are the conditions chosen for the reversible reaction in stage 2 of the contact process?

Answer 23

The conditions chosen for this reversible reaction are usually:

a pressure of 2 atmospheres (200kPa)
a temperature of 450C
a vanadium(V) oxide catalyst, V2O5.

Under these conditions, the equilibrium yield of sulfur trioxide is about 96%.

Question 24

What factors determine the pressure chosen in stage 2 of the Contact process?

Answer 24

In the balanced equation for the reaction in stage 2, there are 3 mol of gas on the left, but only 2 mol of gas on the right. If pressure is increased, then equilibrium position moves to the right and the equilibrium yield of sulfur trioxide increases. However, in this reaction, the equilibrium position is already far to the right. Hence, there is no need for high pressures as it would end up being expensive and potentially dangerous.

Question 25

What factors determine the temperature chosen in stage 2 of the Contact process?

Answer 25

The forward reaction in stage 2 is exothermix, so the backward reaction is endothermic. If temperature is increased, the equilibrium position moves to the left and the equilibrium yield of sulfur trioxide decreases. A high equilibrium yield is favoured by a low temperature.

The temperature chosen is a compromise: low enough for a reasonable equilbirum yield, but high enough for a reasonable rate of reaction. In addition, the vanadium(V) oxide catalyst only works above 380C.

Question 26

What is stage 3 of the Contact process?

Answer 26

In stage 3, sulfur trioxide is converted to sulfuric acid.

Question 27

What is the problem with stage 3 of the Contact process and how is it managed?

Answer 27

The reaction between sulfur trioxide and water in stage 3 is very exothermic. It would produce a hazardous acidic mist, so it is carried out in 2 steps:

1. sulfur trioxide is passed through concentrated sulfuric acid (made previously) to make a compound called oleum (H2S2O7)
2. The oleum is then added to water, and the reaction makes a larger volume of concentrated sulfuric acid.

Question 28

How is alcohol made from renewable raw materials?

Answer 28

Renewable raw materials can be replaced and in principle should not run out. Ethanol is made from plant sugars using fermentation, which relies on single-celled fungi called yeast. Yeast cells contain enyzmes that catalyse the conversion of glucose solution to carbon dioxide and ethanol.

Question 29

How can you carry out fermentation in a school laboratory and what conditions are needed?

Answer 29

It can be carried out using simple apparatus as shown below (limewater will become milky white due to CO2). Yeast cells become inactive if the temperature is too low, and their enzymes become denatured and stop working above about 50C. This means that fermentation is carried out at about 35C under normal atmospheric pressure. Industrial fermentation uses the same conditions but with more complex equipment.

Question 30

How is alcohol made from non-renewable raw materials?

Answer 30

Non-renewable raw materials are used faster than they can be replaced - they will run out one day if you keep using them. Ethene is obtained from crude oil, which is a non-renewable raw material. It can be produced by the hydration of ethene.

Question 31

Why can’t the hydration of ethene be done in a school laboratory?

Answer 31

It is only suitable as an industrial process because it needs a temperature of 300C, and a pressure of 60 atm in the presence of a phosphoric acid catalyst.

Question 32

What are the other differences between the two processes for making ethanol?

Answer 32

Question 33

What is an ore?

Answer 33

An ore is a rock or mineral that contains enough metal (or metal compound) to make it economical to extract the metal - the value of the metal is more than the cost of extracting it.

Question 34

What metal compound is found in malachite?

Answer 34

Copper carbonate

Question 35

What metal compound is found in bauxite?

Answer 35

Aluminium oxide

Question 36

What metal compound is found in haematite?

Answer 36

Iron(III) oxide

Question 37

What happens to the metal ore?

Answer 37

An ore must be mined, and then processed to separate the metal compound from the other substances in the ore. The metal is extracted from the pure metal compound using chemical reactions and the method chosen to extract the metal depends on the position in the reactivity series.

Question 38

What is the reactivity series?

Answer 38

Question 39

How are different metals extracted based on the reactivity series?

Answer 39

In theory, all metals could be extracted from their compounds using electrolysis, but electricity is expensive.

If the metal is less reactive than carbon, you can heat the compounds with carbon or carbon monoxide (reduction with carbon) and this is a much cheaper method.

If it is more reactive than carbon, electrolysis is used.

Question 40

How is copper extracted?

Answer 40

Copper can be extracted from copper (II) sulfide in two stages.

Question 41

How is the extarction of copper with carbon a redox reaction?

Answer 41

Copper(II) oxide loses oxygen and is reduced
Carbon gains oxugen and is oxidised.

Carbon is acting as a reducing agent.

Question 42

How else can copper(II) oxide be reduced to copper?

Answer 42

Question 43

How can you reduce copper(II) oxide with charcoal?

Answer 43

Question 44

What is a blast furnace?

Answer 44

Iron is extracted from its ore using a large reaction container called a blast furnace. Modern blast furnaces can be around 30m high and produce about 10000 tonnes of iron per day.

Question 45

What is put into a blast furnace?

Answer 45

These raw materials are added to the top of the blast furnace:

iron ore, such as haematite, which contains iron(III) oxide.
coke, which is mostly carbon, and is made by heating coal in the absence of air.
limestone, which is used to purify the iron.

Hot air is forced in at the bottom of the blast furnace.

Question 46

What reactions happen in a blast furnace?