Question

Sodium sulphate is soluble in water whereas barium sulphate is sparingly soluble because (a) the hydration energy of sodium sulphate is more than its lattice energy (b) the lattice energy of barium sulphate is less than its hydration energy (c) the lattice energy has no role to play in solubility (d) the hydration energy of sodium sulphate is less than its lattice energy

Short answer

Option (a): The hydration energy of sodium sulphate is more than its lattice energy.

Step-by-step solution

Understanding Solubility

Solubility depends on the balance between lattice energy and hydration energy. A compound is soluble if its hydration energy is greater than its lattice energy.

Analyzing Sodium Sulphate

Sodium sulphate is soluble. This indicates that the hydration energy of sodium sulphate is greater than its lattice energy. Thus, option (a) is a probable reason for its solubility.

Evaluating Barium Sulphate

Barium sulphate is sparingly soluble. This suggests its lattice energy is not less than its hydration energy, thus eliminating option (b). Additionally, options (c) and (d) do not provide a valid explanation for the observed solubility patterns.

Conclusion

Given the reasoning above, the correct explanation for sodium sulphate's solubility and barium sulphate's sparing solubility is because the hydration energy of sodium sulphate is more than its lattice energy, supporting option (a) only.

Key concepts

Hydration Energy

Hydration energy is a key concept in understanding why certain compounds dissolve in water while others do not. It refers to the amount of energy released when ions from a compound interact with water molecules. Essentially, when a compound such as sodium sulphate is introduced to water, the polar water molecules surround and interact with the ions, which stabilizes the compound in solution.

This energy needs to be sufficient to overcome the lattice energy, which is the energy holding the ions together in the solid state. When the hydration energy is higher than the lattice energy, the compound is more likely to dissolve, as seen with sodium sulphate. This is because enough energy is released during hydration to break apart the lattice structure, thus allowing the ions to stay dissolved in the water.

Understanding the balance between hydration energy and lattice energy is fundamental in predicting the solubility of inorganic compounds.

Lattice Energy

Lattice energy plays a crucial role in the solubility of ionic compounds. It is the energy required to separate one mole of a solid ionic compound into gaseous ions. This energy is a measure of the forces holding the ions together in the crystal lattice.

For a salt to dissolve, its lattice energy must be lower than the energy released upon hydration (hydration energy). This is because the energy needed to break the ionic bonds in the solid must be compensated by the energy released when ions are solvated. If the lattice energy is overwhelmingly large, as in the case of barium sulphate, the compound tends to be less soluble. This is because the energy required to separate the ions from each other is not fully compensated by the hydration energy.

Thus, lattice energy is an opposing force to hydration energy, and its predominance can result in compounds like barium sulphate being sparingly soluble.

Inorganic Chemistry

Inorganic chemistry is the branch of chemistry dealing with inorganic compounds, which encompass a vast array of substances, including salts, minerals, and metals. Understanding the behavior of compounds such as sodium sulphate and barium sulphate in water ties directly into the principles of inorganic chemistry.

This field often focuses on the balance of forces and energies, like lattice and hydration energies, that dictate the physical and chemical properties of substances. These energies help to understand reactions, bonds, and solubility of compounds without the presence of carbon-hydrogen bonds, which is a typical characteristic of organic chemistry.

In context, while studying the solubility of various inorganic compounds, one explores how various ions interact with water and how strongly they are held in their solid forms. These insights are imperative for applications ranging from material science to pharmaceuticals, where the solubility of compounds translates into effective functionality or biological activity.