10.2 Fertilisers
- Syllabus
- 0620–2026–2027
- Topic
- 10.2
- Level
- —
Learning objectives
Recognise ammonium and nitrate fertilisers
Ammonium salts and nitrates are used as fertilisers. They supply nitrogen in a form that can support plant growth.
| Substance | Formula clue | Why it matches |
|---|---|---|
| ammonium nitrate | NH₄NO₃ | contains ammonium, NH₄⁺, and nitrate, NO₃⁻ |
| ammonium sulfate | (NH₄)₂SO₄ | is an ammonium salt |
| potassium nitrate | KNO₃ | is a nitrate |
To recognise a suitable example from a name or formula, look for the ammonium ion, NH₄⁺, or the nitrate ion, NO₃⁻. A compound may contain one of these ions or both.
Ammonia, NH₃, is not itself an ammonium salt. Also keep nitrate, NO₃⁻, distinct from nitrogen gas, N₂.
Choose compounds for an NPK fertiliser
NPK fertilisers provide the elements nitrogen (N), phosphorus (P) and potassium (K) for improved plant growth.
| Nutrient supplied | Symbol | Common formula clue |
|---|---|---|
| nitrogen | N | NH₄⁺ or NO₃⁻ |
| phosphorus | P | a phosphate ion such as PO₄³⁻ |
| potassium | K | K in the compound formula |
When choosing compounds, scan the complete formula of each substance and record which of N, P and K it supplies. The chosen compound or mixture must cover all three nutrients without counting the same symbol twice.
For example, ammonium phosphate supplies nitrogen and phosphorus, while potassium sulfate supplies potassium. Together they provide N, P and K.
An NPK fertiliser may be a mixture: every individual compound does not need to contain all three elements, but the full fertiliser must provide all three. P means phosphorus and K means potassium.