CDS Chemistry · Industrial and Applied Chemistry
Fertilizers
What fertilizers supply (nitrogen, phosphorus, potassium), which compounds are nitrogen fertilizers, and how too much nitrate poisons groundwater.
Why this matters
Three CDS questions, from 2016, 2021 and 2025. Each is one fact: which nutrient fertilizers do not carry, which compound is not a nitrogen fertilizer, and which fertilizer pollutes groundwater.
Concept 1 of 2: What fertilizers supply
Definition
The facts:
- Fertilizers supply the major nutrients N, P and K.
- Nitrogen fertilizers: urea (NH₂)₂CO (46% N), ammonium sulphate (NH₄)₂SO₄, ammonium nitrate NH₄NO₃, calcium ammonium nitrate.
- Nitrogen gas, N₂, is not a fertilizer: most plants cannot use it until it is fixed by bacteria or by industry.
- Phosphorus: superphosphate. Potassium: muriate of potash (KCl).
- Micronutrients such as iron, zinc and boron are not usually in fertilizers; they come from manure and the soil.
Practice this concept3 quick reps
The same idea in a real exam question:
Example 1 · Industrial and Applied Chemistry · Fertilizers
Nitrogen gas is not a fertilizer
Iron is not an NPK nutrient
Concept 2 of 2: Nitrate pollution of groundwater
Definition
The effect:
- Excess nitrogen fertilizer → nitrate leaches into groundwater.
- Nitrate in drinking water causes methaemoglobinaemia (blue baby syndrome) in infants.
- Run-off of fertilizer into lakes also feeds algal growth (eutrophication).
| Fertilizer | Moves into groundwater? | Harm |
|---|---|---|
| Nitrogen (as nitrate) | Yes — very soluble | Blue baby syndromeQ |
| Phosphate | Little — held by soil | Eutrophication in lakes via run-off |
| Potassium | Little — held by soil | Rarely a problem |
Practice this concept2 quick reps
The same idea in a real exam question:
Example 2 · Industrial and Applied Chemistry · Fertilizers
Nitrate, not phosphate, reaches groundwater
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (2)
What fertilizers supply4 rows
Nitrate pollution of groundwater3 rows
| Fertilizer | Moves into groundwater? | Harm |
|---|---|---|
| Nitrogen (as nitrate) | Yes — very soluble | Blue baby syndromeQ |
| Phosphate | Little — held by soil | Eutrophication in lakes via run-off |
| Potassium | Little — held by soil | Rarely a problem |
Watch out for (3)
- Nitrogen gas is not a fertilizer→ What fertilizers supply
- Iron is not an NPK nutrient→ What fertilizers supply
- Nitrate, not phosphate, reaches groundwater→ Nitrate pollution of groundwater
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