3.3Chemistry In Society
Fertilisers — SQA National 5 Chemistry — SQA National 5 Chemistry Revision Notes & Topical Questions
5 min read 2 parts Lesson 3 of 5
Section 1 of 2Essential elements and fertiliser requirements
- Growing crops remove essential nutrients from the soil; fertilisers restore these nutrients:
- Nitrogen (N)Essential for leaf growth and protein synthesis.
- Phosphorus (P)Vital for healthy root system development.
- Potassium (K)Crucial for flower and fruit production and disease resistance.
- Fertilisers must be soluble in water so plant roots can absorb them through soil water.
Section 2 of 2Industrial manufacture of fertilisers
1The Haber Process (Production of ammonia)4 points
- Raw materials: Nitrogen from air and hydrogen from natural gas (methane).
- Equation: N2(g) + 3H2(g) ⇌ 2NH3(g)
- Conditions: Iron catalyst, moderately high temperature (~450 °C), high pressure (~200 atm).
- Unreacted nitrogen and hydrogen gases are recycled back through the catalyst chamber to increase efficiency.
2The Ostwald Process (Production of nitric acid)3 points
- Raw materials: Ammonia, oxygen, and water.
- Catalyst: Platinum gauge at ~800 °C.
- Ammonia is oxidised in stages to nitrogen monoxide, nitrogen dioxide, and finally nitric acid (HNO3).
3Synthetic fertiliser production4 points
- Ammonia reacts with acids to produce ammonium salts:
- Ammonia + Nitric acid → Ammonium nitrateNH3 + HNO3 → NH4NO3
- Ammonia + Sulfuric acid → Ammonium sulfate2NH3 + H2SO4 → (NH4)2SO4
- Ammonia + Phosphoric acid → Ammonium phosphate: 3NH3 + H3PO4 → (NH4)3PO4
4Percentage mass calculation
- % of element = (total mass of element in formula / GFM) × 100%
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🌳 Student Search Tree & Frequently Asked Exam Questions: fertilisers
Step-by-step problem-solving guide, mark scheme criteria, and experimental error analysis curated by Dr. Khaled Dabour (DABOURHUB).
1. Identify all given values and convert non-standard units, 2. State the primary formula or physiological/chemical principle, 3. Calculate to 3 significant figures and clearly state units.
Avoid confusing independent vs dependent variables in practical questions. In calculation questions, double-check percentage change formula: (change / original) × 100.
Where can I find fertilisers past paper questions by topic with the mark scheme?
On DABOURHUB every fertilisers question is grouped by syllabus point and shown with the mark-scheme wording, so you can see exactly which sentence earns the mark instead of scrolling through whole year papers.
What is the most common fertilisers exam question and why do students lose marks on it?
The repeated pattern on IGCSE papers is a short stem that asks you to apply fertilisers and then justify it with a command word (explain, suggest, compare). Marks are lost by stating the fact without linking it back to the wording of the question, so each fertilisers item here is written as a full-mark answer.
Is there an alternative to Save My Exams or Physics and Maths Tutor for fertilisers?
Yes: the fertilisers notes, topical questions and MCQ quizzes on this site follow the same syllabus headings as the official specification, and they open straight from the search result with no download step.
How do I revise fertilisers in two weeks before the exam?
Three passes: read the fertilisers notes once, then do the topical questions and mark them against the mark scheme, then redo only the ones you missed. The quiz on the page gives instant feedback so the third pass takes minutes rather than an evening.