Problem 36 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following substances is used as a fertilizer? (a) \(\mathrm{Ca}(\mathrm{CN})_{2}\) (b) \(\mathrm{CaSO}_{4}\) (c) \(\mathrm{K}_{2} \mathrm{SO}_{4} \cdot \mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3} .14 \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2} \mathrm{H}_{2} \mathrm{O} \cdot 2\left(\mathrm{CaS} \mathrm{O}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\right)\)

Step-by-Step Solution

Answer

The substance used as a fertilizer is (d) \( \mathrm{Ca} (\mathrm{H}_{2} \mathrm{PO}_{4})_{2} \cdot \mathrm{H}_{2} \mathrm{O} \cdot 2 (\mathrm{CaSO}_{4} \cdot 2\mathrm{H}_{2} \mathrm{O}) \).

Step 1: Identifying fertilizers

Fertilizers are substances that supply essential nutrients to plants, such as nitrogen, phosphorus, and potassium. We need to recognize which compounds among the given options supply these nutrients.

Step 2: Analyzing the options

Let’s examine each option: (a) \( \mathrm{Ca} ( \mathrm{CN} )_{2} \) is calcium cyanamide and primarily used as a nitrogen fertilizer.(b) \( \mathrm{CaSO}_{4} \) is gypsum, used as a soil conditioner but not typically for fertilization purposes.(c) \( \mathrm{K}_{2} \mathrm{SO}_{4} \cdot \mathrm{Al}_{2} \left( \mathrm{SO}_{4} \right)_{3} \cdot 14 \mathrm{H}_{2} \mathrm{O} \) is potash alum which is not used as a fertilizer.(d) \( \mathrm{Ca} \left( \mathrm{H}_{2} \mathrm{PO}_{4} \right)_{2} \cdot \mathrm{H}_{2} \mathrm{O} \cdot 2 \left( \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O} \right) \) is superphosphate, which contains phosphorus and is used as a fertilizer.

Step 3: Selecting the correct option

Based on the analysis, options (a) and (d) have usage as fertilizers. However, (d) \( \mathrm{Ca} \left( \mathrm{H}_{2} \mathrm{PO}_{4} \right)_{2} \cdot \mathrm{H}_{2} \mathrm{O} \cdot 2 \left( \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O} \right) \) is specifically known as superphosphate, commonly used as a phosphate fertilizer. Therefore, option (d) is the most recognized fertilizer among the ones given.

Key Concepts

Nutrient Supply in Agriculture

Agriculture relies heavily on the supply of essential nutrients to ensure healthy plant growth and high yields. These nutrients are primarily supplied by fertilizers, which play a vital role in modern farming. The most crucial nutrients include nitrogen, phosphorus, and potassium—often abbreviated as NPK. These elements are considered the "big three" nutrients as they are essential to the biological functions of plants.
- **Nitrogen (N):** Vital for plant growth, it is a major component of chlorophyll, which plants use in photosynthesis. Nitrogen is also a critical component of amino acids, the building blocks of proteins.
- **Phosphorus (P):** Crucial for energy transfer in plants, it helps in photosynthesis and nutrient movement within the plant. Phosphorus is also vital for root development and strengthening plant stalks.
- **Potassium (K):** Important for building resistance to diseases, potassium improves plant hardiness and crop quality, and aids in water regulation within the plant.
Farmers carefully manage the nutrient supply by using fertilizers to maintain a balance that satisfies the plants' needs and maximizes crop productivity.

Chemical Compounds Used as Fertilizers

Fertilizers are composed of various chemical compounds that provide specific nutrients to plants. Different types of fertilizers exist based on the primary nutrient they supply: nitrogen, phosphorus, or potassium. Each type of fertilizer serves a distinct purpose and improves different aspects of plant growth and soil health.
- **Nitrogen fertilizers:** Compounds such as ammonium nitrate (\[\text{NH}_4\text{NO}_3\]) or urea (\[\text{CO(NH}_2\text{)}_2\]) are widely used to supply nitrogen, which is essential for leafy growth.
- **Phosphate fertilizers:** These contain phosphorus and include compounds like calcium dihydrogen phosphate (\[\text{Ca(H}_2\text{PO}_4\text{)}_2\]). They promote strong root development and enhance energy storage and transfer within plants.
- **Potash fertilizers:** Typically contain potassium chloride (\[\text{KCl}\]) or potassium sulfate (\[\text{K}_2\text{SO}_4\]), which enhance disease resistance and improve water efficiency.
Choosing the right fertilizer depends on the specific nutrient deficiencies in the soil and the needs of the crops being grown. Soil testing often informs these decisions.

Superphosphate as a Fertilizer

Superphosphate is a widely recognized phosphate fertilizer known for its effectiveness in providing essential phosphorus to crops. It is especially beneficial for root development and early plant growth. Superphosphate is made by reacting phosphate rock with sulfuric acid, producing a mixture of calcium dihydrogen phosphate and calcium sulfate.
- Superphosphate helps increase agricultural output by improving stiff root systems and promoting vigorous growth. Farmers targeting increased crop yields often rely on this type of fertilizer.
- There are two main types: **Single Superphosphate (SSP)** and **Triple Superphosphate (TSP).** While SSP contains approximately 20% phosphorus, TSP is more concentrated, with about 44% phosphorus.
Using superphosphate ensures a steady supply of phosphate, essential for photosynthesis and energy transfer within plants. It is typically applied to the soil before planting, allowing phosphorus to be readily available as seeds begin to germinate and grow. This makes it a staple in the cultivation of a wide variety of crops, from cereals to fruits and vegetables.