12.3 Chemistry in Agriculture and Industries

1. Fertility of Soil

• Fertility is enhanced by applying chemical substances produced in industries.

• Limestone (CaCO₃) is a valuable resource found in Sunamgonj district and Saint Martin Island. It is used in cement production.

• If soil is acidic (increased H⁺ concentration), limestone is applied to reduce acidity.

• Limestone reacts with H⁺ to produce calcium ions (Ca²⁺), carbon dioxide, and water, lowering acidity.

• Reaction: CaCO₃ + 2H⁺ → Ca²⁺ + CO₂ + H₂O

2. Urea

• Urea (NH₂-CO-NH₂) is produced by heating ammonium carbamate (NH₂COONH₂) at high pressure (130°C–150°C).

• Formation of ammonium carbamate:

• CO₂ + 2NH₃ → NH₂COONH₂

• Urea is used as fertilizer in agriculture, providing nitrogen to plants.

• Reaction with Urease Enzyme: Urea reacts with water in the presence of Urease Enzyme to release ammonium ions (NH₄⁺).

• NH₂CO-NH₂ + 3H₂O → 2NH₄⁺ + 2OH⁻ + CO₂

3. Ammonium Sulphate

• Ammonium sulphate (NH₄)₂SO₄ is produced by reacting ammonia (NH₃) with sulphuric acid (H₂SO₄).

• 2NH₃ + H₂SO₄ → (NH₄)₂SO₄ + H₂O

• It is used in agriculture to reduce alkali content in soil, providing nitrogen and sulphur to plants.

4. Chemicals in Processing Agricultural Commodities

• Processing: Involves using chemicals to preserve agricultural commodities (fruits, vegetables, fish) and prevent decay.

• Ripening Fruits: Traders sometimes use calcium carbide (CaC₂) to ripen fruits like mangoes, which produces acetylene gas.

• CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂

• Ethylene Gas: Naturally released by ripe fruits, it helps other fruits ripen, but excessive use of carbide (acetylene) can be harmful.

5. Chemicals in Preserving Agricultural Commodities

• Preservation Methods: Ice, vinegar, and salt are commonly used to preserve agricultural commodities.

• Formalin: Not safe for food preservation; it can be harmful or fatal if ingested.

• Vinegar: Used to preserve tomatoes, green mangoes, etc., and is safe for consumption.

6. Recommended Food Preservatives

• Safe Preservatives: Substances approved by the World Health Organization (WHO) such as sodium benzoate, benzoic acid, vinegar, and salt solutions.

• Unauthorized Preservatives: Ethylene and acetylene, which can harm the body.

7. Industrial Disposal and Environmental Pollution

• Industrial waste, such as heavy metals (chromium, lead, mercury, cadmium), is harmful when it enters soil and water.

• Effects of Industrial Waste: These metals harm kidneys, liver, and can cause death when ingested via contaminated plants or water.

• Caustic Soda (NaOH): Waste from soap and detergent factories can increase water alkalinity, harming aquatic life.