Unit 4: Fertilizers and Pesticides

Course Code: CHM-DSC-353

Paper Name: Industrial Chemistry

1. Introduction to Fertilizers

Fertilizers are natural or synthetic substances containing chemical elements that improve the growth and productiveness of plants.

Essential Nutrients

• Primary Nutrients: Nitrogen (N), Phosphorus (P), and Potassium (K).
• Secondary Nutrients: Calcium, Magnesium, and Sulphur.
• Micronutrients: Iron, Manganese, Boron, Zinc, etc.

NPK Value: A label on fertilizer bags (e.g., 10-20-10) indicating the percentage by weight of Nitrogen, Phosphorus (as P2O5), and Potassium (as K2O).

2. Nitrogenous Fertilizers: Urea

Nitrogen is essential for the synthesis of chlorophyll and proteins.

Manufacturing of Urea [NH2CONH2]

Urea is the most important nitrogenous fertilizer due to its high nitrogen content (~46.6%). It is produced by the reaction of liquid ammonia and liquid carbon dioxide at high pressure and temperature.

[Image of Urea production process flow diagram]

• Reaction: 2NH3 + CO2 ⇌ NH2COONH4 (Ammonium Carbamate) → NH2CONH2 + H2O
• Forms: Usually sold as "Prills" or granules to prevent caking and facilitate easy spreading.

3. Phosphatic Fertilizers

Phosphorus is crucial for root development and energy transfer in plants.

• Single Superphosphate (SSP): Produced by reacting phosphate rock with Sulphuric acid. It contains 16-20% P2O5.
• Triple Superphosphate (TSP): Produced by reacting phosphate rock with Phosphoric acid. It is much more concentrated (~45-50% P2O5).

4. Pesticides: Classification

Pesticides are chemicals used to kill or control pests that damage crops.

5. Environmental Impacts

While agro-chemicals increase food production, they pose significant environmental risks.

• Eutrophication: Runoff of nitrate and phosphate fertilizers into water bodies causes excessive algae growth, depleting oxygen and killing aquatic life.
• Bioaccumulation: Persistent pesticides (like DDT) accumulate in the fatty tissues of organisms and increase in concentration up the food chain (Biomagnification).
• Soil Degradation: Excessive use of chemical fertilizers can alter soil pH and kill beneficial soil microorganisms.

6. Exam Focus: Tips and FAQs

Exam Tips

• Urea Reaction: Memorize the two-step synthesis involving ammonium carbamate as an intermediate.
• Pesticide Safety: Mention the shift from organochlorines (DDT) to organophosphates (Malathion) because the latter are more biodegradable.
• Calculation: Be prepared to calculate the percentage of Nitrogen in Urea based on its molecular formula.

Frequently Asked Questions

Q: Why is DDT banned in many countries?
A: Because it is non-biodegradable, persists in the environment for decades, and causes reproductive failure in birds (thinning of eggshells).

Q: What is the composition of Bordeaux mixture?
A: It is a mixture of Copper Sulphate (CuSO4) and Slaked Lime [Ca(OH)2].

Q: What does the term "Bio-pesticide" mean?
A: These are pesticides derived from natural materials like animals, plants (e.g., Neem oil), and certain minerals.