Problem 62 - A Complete Resource Book in Chemistry for JEE Main

Question

The compound formed when gypsum is dissolved in aqueous ammonium sulphate solution is (a) \(\mathrm{CaSO}_{4} \cdot \mathrm{NH}_{3} \mathrm{Cl} \cdot \mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{CaSO}_{4} \cdot\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4} \cdot \mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{CaCl}_{2} . \mathrm{NH}_{4} \mathrm{Cl} .2 \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{CaCl}_{2} \cdot\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4} \cdot \mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

The compound formed is \( \text{CaSO}_4 \cdot (\text{NH}_4)_2\text{SO}_4 \cdot \text{H}_2\text{O} \) (Option b).

Step 1: Understand the Composition of Gypsum

Gypsum is chemically known as calcium sulfate dihydrate, with the formula \( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \). It consists of calcium, sulfate ions, and water molecules.

Step 2: Analyze the Reaction Environment

The problem specifies that gypsum is dissolved in an aqueous ammonium sulfate solution, represented by \( (\text{NH}_4)_2\text{SO}_4 \). This provides ammonium ions and extra sulfate ions in solution.

Step 3: Predict the Possible Products

When gypsum dissolves in ammonium sulfate, different ionic interactions can occur. Calcium ions from gypsum can potentially form a new compound with sulfate or ammonium ions.

Step 4: Identify the Correct Product Based on Choices

Review the given options: The most logical compound that can form combines calcium (from gypsum) with sulfate ions, and potentially, water. Considering the reaction environment, the correct compound is \( \text{CaSO}_4 \cdot (\text{NH}_4)_2\text{SO}_4 \cdot \text{H}_2\text{O} \).

Step 5: Verify and Conclude

Verify the answer by checking which option corresponds to the compound identified. Option \( (b) \) matches the expected outcome, where calcium sulfate combines with ammonium sulfate and water.

Key Concepts

Gypsum

Gypsum is a widely used mineral that holds great importance in construction and manufacturing. It is recognized by its chemical name calcium sulfate dihydrate with the formula \( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \). This means each molecule of gypsum contains one calcium ion, one sulfate ion, and two water molecules that are part of its crystal structure.

• Gypsum is commonly used in drywall, plaster, and as a fertilizer.
• The presence of water in its structure makes it soft and flexible.

When gypsum undergoes reactions with other chemical compounds, its structure and components, particularly the calcium and sulfate ions, may form new compounds. Understanding these interactions is crucial when predicting the outcomes of such chemical reactions.

Ammonium Sulfate

Ammonium sulfate, represented by the chemical formula \((\text{NH}_4)_2\text{SO}_4\), plays a vital role in various industrial and agricultural applications. It consists of ammonium ions \((\text{NH}_4)^+\) which readily dissolve in water, releasing nitrogen, an essential nutrient for plant growth.

• It is often used as a fertilizer due to its high nitrogen content which enhances plant growth.
• The sulfate component contributes sulfur, another important plant nutrient.

When gypsum dissolves in ammonium sulfate solutions, these dissolved ions contribute to potential reactions where new compounds can form. Understanding how these ions behave in solution is key to predicting the outcome of dissolving gypsum in an ammonium sulfate solution.

Calcium Sulfate

Calcium sulfate is a common compound in chemistry that appears in various forms, including gypsum. Its chemical formula is \( \text{CaSO}_4 \). In its anhydrous form, it's known as "dry" calcium sulfate, or anhydrite, while if it contains water, it forms gypsum.

• It is used in the food industry as a coagulant in products like tofu.
• Calcium sulfate can also act as a desiccant (drying agent).

When mixed with solutions like ammonium sulfate, calcium ions \((\text{Ca}^{2+})\) and sulfate ions \((\text{SO}_4^{2-})\) can interact to form new chemical compounds. In a reaction environment involving ammonium sulfate, the extra sulfate ions can combine with calcium to create a solid that changes depending on the conditions, such as the concentration of ions and the presence of other chemicals.

Aqueous Solutions

Aqueous solutions are a fundamental concept in chemistry, where a substance is dissolved in water, making it a solvent solution. When substances like ammonium sulfate dissolve in water, they dissociate into their component ions.

• Water's polar nature allows it to dissolve a wide variety of substances, which is why it's often called the "universal solvent."
• Aqueous solutions can conduct electricity due to the presence of free-moving ions.

In the case of gypsum being dissolved in an aqueous ammonium sulfate solution, water enables the dissociation of both ammonium sulfate and gypsum. This creates a chemical environment where ions can interact and form new compounds, such as the combination of calcium, sulfate, and ammonium to create calcium sulfate ammonium sulfate hydrate. Understanding how dissolved ions interact is crucial in predicting the products of such reactions.