Haber Process and use of NPK Fertilisers (10.4) (M)

Question 1

What can the Haber process be used to do?

Answer 1

manufacture ammonia

Question 2

What can ammonia be used to do?

Answer 2

to produce nitrogen-based fertilisers

Question 3

What are the raw materials for the Haber process?

Answer 3

nitrogen and hydrogen

Question 4

What is a source of nitrogen?

Answer 4

air

Question 5

What is a source of hydrogen?

Answer 5

By reacting natural gas (methane normally) with steam

Question 6

What happens to hydrogen and nitrogen in the Haber process to manufacture ammonia?

Answer 6

The purified gases are passed over a catalyst of iron at a high temperature (about 450°C) and a high pressure (about 200 atmospheres)

Question 7

What is type of reaction is the one in the hater process?

Answer 7

a reversible reaction

Question 8

What is the equation for the Haber process?

Answer 8

Question 9

The Haber process is reversible, what does this mean?

Answer 9

Only some of the hydrogen and nitrogen reacts to form ammonia.

Some of the ammonia produced breaks down into nitrogen and hydrogen

Question 10

How is ammonia collected after being produced?

Answer 10

It is cooled, the ammonia liquefies and is removed

Question 11

What happens to the hydrogen and nitrogen in the Haber process that don’t react?

Answer 11

They are recycled

to save money and increase effective overall yield

Question 12

In the Haber process, the forward reaction is (…) and the backward reaction is (…)

Answer 12

exothermic

endothermic

Question 13

Why is iron used in the Haber process?

Answer 13

Iron is a catalyst for the reaction.

It increases the rate of the reaction without being used up in the reaction (what a catalyst does)

Doesn’t change equilibrium position

Question 14

What is the problem with using very high pressures (and temperatures) in the Haber process?

Answer 14

expensive and dangerous

Question 15

Explain how the commercially used conditions for the Haber process are related to the availability and cost of raw materials and energy supplies

Answer 15

You need to use natural gas to heat the reaction and to get the hydrogen. If the price of these goes up, the cost of fertiliser increases

if in low availability, the price will be high

Question 16

Compounds containing what are used in an NPK fertiliser?

Answer 16

(the elements) nitrogen, phosphorus and potassium

Question 17

Why are (NPK) fertilisers used?

Answer 17

to improve agricultural productivity

fertilisers provide mineral ions for healthy growth

Question 18

What do nitrogen, phosphorus and potassium each provide as a fertiliser to plants?

Answer 18

N - healthy foliage (leaves)

P - strong roots

K - healthy growth

Question 19

What are NPK fertilisers?

Answer 19

formulations of various salts containing appropriate percentages of the elements nitrogen, phosphorus and potassium

Question 20

How can industrial production of NPK fertilisers be achieved?

Answer 20

using a variety of raw materials in several integrated processes

Question 21

What can ammonia can be used to manufacture? (not nitrogen-based fertiliser answer, this is a chemical one)

Answer 21

ammonium salts and nitric acid

Question 22

How can potassium chloride, potassium sulfate and phosphate rock be obtained?

Answer 22

by mining

Question 23

Phosphate rock is insoluble in water and so cannot be taken up by plants, what does this mean?

Answer 23

phosphate rock cannot be used directly as a fertiliser

so must be converted into salts (which are soluble)

Question 24

How is phosphate rock treated for use in fertilisers?

Answer 24

Phosphate rock is treated with nitric acid or sulfuric acid to produce soluble salts that can be used as fertilisers

Question 25

What is the salt produced when phosphate rock is treated with nitric acid?

Answer 25

Calcium nitrate (which can be used as a fertiliser) and phosphoric acid, the latter is neutralised with ammonia to make ammonium phosphate

Question 26

What is the salt produced when phosphate rock is treated with sulfuric acid?

Answer 26

Single superphosphate, which is a mixture of calcium sulfate and calcium phosphate

Question 27

What is the salt produced when phosphate rock is treated with phosphoric acid?

Answer 27

Triple superphosphate (calcium phosphate)

Question 28

How are fertilisers produced in the lab?

Answer 28

Do neutralisation one time with indicator

Do it without indicator second time

Evaporate gently

This is small scale and takes a short time - easier to do

Question 29

How are fertilisers produced in industrial processes?

Answer 29

Large scale production

Starts with raw materials - cheaper than buying in ammonia and acid or other compounds

It is a continuous process - keep adding raw materials as is cheaper to do so

Question 30

Why has the demand for ammonia has increased?

Answer 30

The world population has increased

So demand for fertiliser (for producing food) has increased

Question 31

What is the purpose of pipe x?

Answer 31

to recycle unreacted hydrogen and nitrogen

Question 32

Key exam technique - 6 points

Suggest and explain why the conditions used to produce ammonia in the Haber process are a temperature of 450 °C and a pressure of 200 atmospheres

Answer 32

reaction is reversible

forward reaction is exothermic so increased temperature lowers the yield of ammonia

a lower temperature would decrease rate of reaction, so that the reaction is too slow

a higher pressure would increase the yield of ammonia because the forward reaction produces the least number of (gaseous) molecules / moles

higher pressures would involve high cost / energy

450^oC gives a reasonable yield at a fast rate

Question 33

2 marker

Why is a temp of 450^oC used in the haber process?

Answer 33

A higher temperature would reduce the yield

A lower temperature would reduce the rate of reaction

Question 34

Why would showing a ratio label of elements in an NPK fertiliser be useful to the farmer?

Answer 34

shows fertilisers are formulations

so farmer can choose fertiliser with required properties

Question 35

2 marks

Why would the haber process cause the closure of mines?

Answer 35

Ammonia/Haber process can be used to make a fertiliser

raw materials for haber process are readily available or haber process is continuous or transport costs are lower

Question 36

What are the three salts/materials that can be obtained by mining?

Answer 36

• potassium chloride
• potassium sulfate
• phosphate rock