Question

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

Short answer

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

Step-by-step solution

Identify the compounds involved

We are given that gypsum (\(\text{CaSO}_4 \cdot 2 \text{H}_2\text{O}\)) is dissolved in an aqueous ammonium sulphate solution (\((\text{NH}_4)_2\text{SO}_4\)). Our task is to find the compound formed from this dissolution.

Predict potential interactions

Upon dissolution, gypsum provides \(\text{Ca}^{2+}\) ions and \(\text{SO}_4^{2-}\) ions, while ammonium sulphate provides \(\text{NH}_4^+\) ions. These ions can potentially interact to form a new compound.

Analyze given options

We need to assess the provided options for the compound formed. Notably, a common product of such reactions is the formation of double salts, which involve both sulfate groups: \(\text{CaSO}_4\) and \((\text{NH}_4)_2\text{SO}_4\).

Compare with assumed products

Typically, when gypsum dissolves in ammonium sulfate, the formation of a compound that includes both calcium sulfate and ammonium sulfate occurs. From the options, \(\text{CaSO}_4\cdot(\text{NH}_4)_2\text{SO}_4\cdot\text{H}_2\text{O}\) mirrors this arrangement.

Key concepts

Gypsum

Gypsum is a soft mineral composed mainly of calcium sulfate dihydrate with the chemical formula \( \text{CaSO}_4 \cdot 2\text{H}_2\text{O} \). It is widely used in the construction industry for building materials and is a vital component of plaster and drywall. Gypsum is naturally occurring and is usually found in sedimentary deposits.
When interacting with other chemicals, gypsum's calcium sulfate component can dissociate, releasing calcium ions \( \text{Ca}^{2+} \) and sulfate ions \( \text{SO}_4^{2-} \). This dissolution process makes gypsum reactive and useful for forming new chemical compounds when mixed with other substances.
Types of Gypsum:

• Selenite: transparent and colorless, fibrous gypsum.
• Alabaster: fine granular variety used for sculptures.
• Rock gypsum: commonly used in plaster and drywall.

Gypsum’s flexibility to dissolve and form new compounds is crucial in various industrial and chemical applications.

Ammonium Sulphate

Ammonium sulphate is an inorganic salt with the formula \((\text{NH}_4)_2\text{SO}_4\). It is primarily used as a soil fertilizer as it provides nitrogen and sulfur, two essential nutrients for plant growth. Prepared by reacting ammonia with sulfuric acid, ammonium sulfate dissolves readily in water, producing ammonium \( \text{NH}_4^+ \) and sulfate \( \text{SO}_4^{2-} \) ions.
In the context of interactions with other chemicals, ammonium sulphate readily dissolves and can participate in forming new compounds. When mixed with gypsum, as in the exercise, the sulfate groups in both compounds can coordinate with the calcium ions, forming double salts.
Ammonium sulphate is not only vital in agriculture but also used in various industries for preparation of pharmaceuticals, purification of proteins, and more.

Chemical Reactions

Chemical reactions involve the transformation of substances through breaking and forming chemical bonds. When gypsum and ammonium sulphate are dissolved in water, a chemical reaction occurs, where ions from the dissolution can rearrange to form new compounds.
Here, the reaction involves:

• Dissolution of gypsum to release \( \text{Ca}^{2+} \) and \( \text{SO}_4^{2-} \) ions.
• Dissolution of ammonium sulphate to release \( \text{NH}_4^+ \) and additional \( \text{SO}_4^{2-} \) ions.
• Possibility of a combination of ions from different origins to form stable compounds.

The key is that a chemical reaction can result in the formation of a double salt in which the components come from different initial substances, highlighting the complexity and versatility of chemistry in naturally occurring and synthetic environments.

Ionic Compounds

Ionic compounds are characterized by the electrostatic forces holding together oppositely charged ions. Typically formed from a metal and a non-metal, such compounds are neutral overall but consist of cations and anions.
In the exercise context, when gypsum and ammonium sulfate are dissolved, the mix of ions in solution can interact to build new ionic compounds, like double salts. These double salts, such as \( \text{CaSO}_4\cdot(\text{NH}_4)_2\text{SO}_4\cdot\text{H}_2\text{O} \), are formed when two distinct salts are held together by the ionic lattice.
Properties of Ionic Compounds:

• Typically have high melting and boiling points.
• Conduct electricity when dissolved in water (or molten).
• Solubility varies widely depending on the nature of the ions and the solvent.

Understanding ionic compounds helps in appreciating how compounds dissolve, interact, and reform in chemical reactions, explaining phenomena like the double salt formation from gypsum and ammonium sulphate.