Problem 44 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is calcium superphosphate? (a) \(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2} \mathrm{H}_{2} \mathrm{O}+\mathrm{CaSO}_{4}\) (b) \(\mathrm{CaSO}_{4}+\mathrm{CaO}\) (c) \(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}+2 \mathrm{CaSO}_{4}\) (d) \(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2} \mathrm{H}_{2} \mathrm{O}+2\left(\mathrm{CaSO}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}\right)\)

Step-by-Step Solution

Answer

Option (a) is calcium superphosphate.

Step 1: Understand the Definition

Calcium superphosphate, also known as superphosphate of lime, is a fertilizer that is produced by the chemical treatment of rock phosphate with sulfuric acid. The chemical formula for calcium superphosphate is typically given as \( \mathrm{Ca(HSO_4)_2} \) or can be represented as \( \mathrm{Ca(H_2PO_4)_2} \) when hydrated. It is commonly associated with phosphates of calcium and additional components such as sulfates.

Step 2: Analyze Each Option

We need to determine which of the given chemical formulas matches the characteristics of calcium superphosphate. This involves recognizing the key components of calcium superphosphate, mainly \( \mathrm{Ca(H_2PO_4)_2} \) and possibly additional calcium sulfate \( \mathrm{CaSO_4} \), since it often contains gypsum.

Step 3: Evaluate Option (a)

Option (a) is \( \mathrm{Ca(H_2PO_4)_2 H_2O + CaSO_4} \). This matches the description of calcium superphosphate, as it contains \( \mathrm{Ca(H_2PO_4)_2} \) along with \( \mathrm{CaSO_4} \) (gypsum), aligning with a combination typically found in superphosphate fertilizers.

Step 4: Evaluate Option (b)

Option (b) is \( \mathrm{CaSO_4 + CaO} \). This option consists only of calcium sulfate and lime (calcium oxide), without any phosphate. This cannot be calcium superphosphate.

Step 5: Evaluate Option (c)

Option (c) is \( \mathrm{Ca_3(PO_4)_2 + 2 CaSO_4} \). This is a mixture of calcium phosphate and calcium sulfate, but lacks the specific hydrogen phosphate component \( \mathrm{Ca(H_2PO_4)_2} \) necessary for superphosphate.

Step 6: Evaluate Option (d)

Option (d) is \( \mathrm{Ca(H_2PO_4)_2 H_2O + 2(CaSO_2 \cdot 2 H_2O)} \). This contains \( \mathrm{Ca(H_2PO_4)_2} \), which is necessary for superphosphate, but the presence of a structure labeled \( \mathrm{CaSO_2 \cdot 2 H_2O} \) is incorrect as it is not a typical part of superphosphate.

Step 7: Conclusion

Having analyzed all options, option (a), \( \mathrm{Ca(H_2PO_4)_2 H_2O + CaSO_4} \), best represents calcium superphosphate because it contains the hydrated calcium dihydrogen phosphate and gypsum, which correspond to the known composition of superphosphate fertilizers.

Key Concepts

Chemical Fertilizers

Chemical fertilizers are vital to modern agriculture, providing essential nutrients that enhance soil fertility and boost plant growth. These fertilizers are chiefly composed of chemicals that supply key nutrients in forms readily available to plants.

• Nitrogen (N), phosphorus (P), and potassium (K) are the primary macronutrients found in most fertilizers.
• Phosphorus, particularly, is crucial for root development, energy transfer, and photosynthesis.
• Chemical fertilizers can be single compounds or mixtures, designed to fulfill specific agricultural needs.

Calcium superphosphate is a prime example of a phosphorus-based fertilizer. It focuses on delivering phosphorus to the plants, thereby enhancing their growth potential. Superphosphates are made by treating phosphate rock with acids, usually sulfuric acid. This process increases phosphate content, making it readily absorbable by plants. Additionally, calcium superphosphate often includes beneficial secondary nutrients such as sulfur in the form of gypsum, which improves overall plant health.

Phosphate Chemistry

Phosphate chemistry deals with compounds containing the phosphate ion, ext{PO}_4^{3−}, which is fundamental to a wide range of agricultural, biological, and industrial applications. Understanding these compounds is key to grasping the role and function of different fertilizers.

• Phosphate ions can form various compounds depending on the cations they are paired with. These combinations affect solubility and availability of phosphorus in soils.
• Phosphates can be combined with calcium to form different types of phosphates, like mono-, di-, and tri-calcium phosphates, each having specific uses and properties.
• Calcium dihydrogen phosphate, ext{Ca(H}_2 ext{PO}_4 ext{)_2}, is a water-soluble form of phosphate used in superphosphates, making it an efficient source of phosphorus for plants.

The study of phosphate chemistry enables the development of different phosphate-based fertilizers not only fulfilling the nutrient demand of plants but also optimizing the usage of natural resources to meet global agricultural needs.

Calcium Compounds

Calcium compounds are integral to both biological and geological systems, playing crucial roles in soil chemistry and plant physiology.

• Calcium is a secondary nutrient essential for plant growth, acting as a soil conditioner and a source of nourishment for plants.
• Calcium compounds in fertilizers, such as gypsum ( ext{CaSO}_4 ext{·2H}_2 ext{O}), enhance soil structure by aiding in water retention and penetration.
• In fertilizers like calcium superphosphate, the presence of calcium not only supports plant structure but also assists in balancing soil pH and reducing soil salinity.

Understanding calcium compounds allows for the development of fertilizers that enhance nutrient uptake, improve plant resilience, and ensure sustainable agricultural practices. Each compound's unique properties can target specific agricultural challenges, promoting healthier plant growth and higher crop yields.