GCSE Chemistry revision

Production and uses of NPK fertilisers

The Haber process and the use of NPK fertilisers (chemistry only)

AQA 4.10.4.2 Foundation & Higher

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Treating insoluble phosphate rock with nitric acid produces phosphoric acid (H₃PO₄) and calcium nitrate (Ca(NO₃)₂).
Example: The produced phosphoric acid is subsequently neutralized with ammonia gas to yield ammonium phosphate, a key soluble component in NPK fertilisers.

Treating phosphate rock with sulfuric acid produces single superphosphate, which is a soluble mixture of calcium phosphate and calcium sulfate (CaSO₄).
Example: Single superphosphate is applied directly to agricultural fields to supply both phosphorus and sulfur nutrients to crops.

Treating phosphate rock directly with phosphoric acid produces triple superphosphate, which consists of pure calcium phosphate (Ca(H₂PO₄)₂).
Example: Triple superphosphate contains a higher percentage of plant-available phosphorus than single superphosphate, promoting stronger root growth in farming.

3. Phosphoric Acid Treatment AQA

Treating phosphate rock directly with phosphoric acid produces triple superphosphate, which consists of pure calcium phosphate (Ca(H₂PO₄)₂).
Example: Triple superphosphate contains a higher percentage of plant-available phosphorus than single superphosphate, promoting stronger root growth in farming.

Scale and Process Type: Industrial fertiliser production operates as a continuous process producing thousands of tonnes per day, whereas laboratory preparation is a small-scale batch process producing only a few grams per run.
Example: In industry, raw materials are continuously fed into automated reactors to produce uninterrupted output, whereas a student in a laboratory performs a single titration step in a flask before re-setting.
Reactant Concentration and Energy Control: Laboratory synthesis uses dilute, safe aqueous solutions at room temperature, whereas industrial manufacturing uses concentrated gases and liquids, utilizing the intense heat released from the exothermic reaction to evaporate water automatically.
Example: Industrial production injects pure ammonia gas into concentrated sulfuric acid so the reaction heat boils off excess water instantly, whereas a lab setup requires manual heating over a Bunsen burner to crystallize the salt.

4. Comparing Industrial vs Laboratory Preparation of Fertilisers AQA

Scale and Process Type: Industrial fertiliser production operates as a continuous process producing thousands of tonnes per day, whereas laboratory preparation is a small-scale batch process producing only a few grams per run.
Example: In industry, raw materials are continuously fed into automated reactors to produce uninterrupted output, whereas a student in a laboratory performs a single titration step in a flask before re-setting.
Reactant Concentration and Energy Control: Laboratory synthesis uses dilute, safe aqueous solutions at room temperature, whereas industrial manufacturing uses concentrated gases and liquids, utilizing the intense heat released from the exothermic reaction to evaporate water automatically.
Example: Industrial production injects pure ammonia gas into concentrated sulfuric acid so the reaction heat boils off excess water instantly, whereas a lab setup requires manual heating over a Bunsen burner to crystallize the salt.

Laboratory preparation uses low-cost glass apparatus (burettes, pipettes, evaporating dishes) with high manual labor per unit mass, while industrial production requires high capital investment for heavy stainless-steel plant infrastructure but operates with minimal labor costs per tonne.
Example: Neutralizing dilute sulfuric acid with aqueous ammonia in a lab requires precise manual titration using a glass burette, whereas an industrial chemical plant uses computer-automated reaction towers.

5. Equipment and Cost Considerations AQA

Laboratory preparation uses low-cost glass apparatus (burettes, pipettes, evaporating dishes) with high manual labor per unit mass, while industrial production requires high capital investment for heavy stainless-steel plant infrastructure but operates with minimal labor costs per tonne.
Example: Neutralizing dilute sulfuric acid with aqueous ammonia in a lab requires precise manual titration using a glass burette, whereas an industrial chemical plant uses computer-automated reaction towers.