Production and uses of NPK fertilisers (chemistry only)
Practise 30 exam-style questions on Production and uses of NPK fertilisers (chemistry only) for AQA GCSE Chemistry. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.
30 questions
1–6 marks each
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20 questions, marked as you go
Sample questions with model answers
Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.
Question 1
2 marks
NPK fertilisers contain compounds of three elements.
Name the three elements.
Model answer
Nitrogen, phosphorus and potassium.
Explanation
N, P and K are the chemical symbols of nitrogen, phosphorus and potassium. Be careful: P is phosphorus, and K (not P) is potassium.
Mark scheme
1 mark
any two of: nitrogen, phosphorus, potassium
do not accept the symbols N, P and K alone; ignore nitrate, phosphate
1 mark
all three correct: nitrogen, phosphorus and potassium
Question 2
2 marks
Triple superphosphate is made by treating phosphate rock with phosphoric acid. Single superphosphate is made by treating phosphate rock with sulfuric acid.
Explain why triple superphosphate contains a higher percentage of phosphorus than single superphosphate.
Model answer
Single superphosphate is a mixture of calcium phosphate and calcium sulfate. The calcium sulfate contains no phosphorus, so it dilutes the phosphate. Triple superphosphate is just calcium phosphate, and the phosphoric acid also adds phosphorus.
Explanation
The acid used decides what else ends up in the product. Phosphoric acid contributes phosphorus itself and produces no calcium sulfate, so the product is richer in phosphorus.
Mark scheme
1 mark
single superphosphate also contains calcium sulfate
1 mark
which contains no phosphorus / dilutes the calcium phosphate
allow phosphoric acid adds extra phosphorus to triple superphosphate
Explain how using NPK fertilisers allows farmers to produce more food.
Model answer
As crops grow, they remove compounds of nitrogen, phosphorus and potassium from the soil. NPK fertilisers replace these elements in soluble forms that plants can absorb, so the crops grow faster and bigger. This gives a higher yield, so more food is produced from the same area of land.
Explanation
Without fertilisers, soil becomes depleted of the elements crops need and yields fall. Fertilisers let farmers grow more food on the land they have.
Mark scheme
1 mark
crops remove nitrogen, phosphorus and potassium from the soil (as they grow)
max 3
1 mark
fertilisers replace these elements / provide them in a soluble form that plants can absorb
1 mark
so crops grow faster / bigger, giving a higher yield
1 mark
so more food is produced from the same area of land
Question 4
4 marks
A student titrates 25.0 cm³ of ammonia solution with sulfuric acid of concentration 0.100 mol/dm³. The ammonia is exactly neutralised by 20.0 cm³ of the acid. 2NH₃ + H₂SO₄ → (NH₄)₂SO₄
Calculate the concentration of the ammonia solution in mol/dm³.
Convert volumes from cm³ to dm³ by dividing by 1000. The equation shows two moles of ammonia react with each mole of sulfuric acid, so double the moles of acid before dividing by the volume of ammonia.
