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

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

Step-by-step solution

Understand the Concept of Solubility

Solubility of a salt in water is determined by the balance between lattice energy and hydration energy. A salt will be soluble if its hydration energy is greater than its lattice energy.

Assess Sodium Sulphate

Sodium sulphate is soluble in water, which means that its hydration energy is more significant than its lattice energy. Therefore, the dissolution process is energetically favorable.

Evaluate Barium Sulphate

Barium sulphate is sparingly soluble. This suggests that its lattice energy is higher than its hydration energy, making the dissolution process energetically unfavorable.

Analyze the Options

The options must be evaluated based on the information about solubility: (a) correct as sodium sulphate's solubility is due to hydration energy being more than lattice energy, (b) incorrect for barium sulphate as lattice energy is greater, (c) incorrect as lattice energy plays a critical role, (d) incorrect for sodium sulphate as hydration energy is more than lattice energy.

Key concepts

Understanding Lattice Energy

Lattice energy is a key factor in determining the solubility of ionic compounds. It refers to the amount of energy required to separate one mole of a solid ionic compound into its gaseous ions. Essentially, it is the energy holding the ions together in the crystalline structure. The higher the lattice energy, the stronger the forces holding the ions together, making the compound less likely to dissolve in water.
In simple terms, if a compound has a high lattice energy, its ions are tightly bound together within the solid structure. This means more energy is needed to break these ionic bonds, reducing solubility. For example, barium sulphate, which has high lattice energy, is sparingly soluble in water, as the energy required to break its ionic bonds is not adequately compensated by the energy released when it dissolves.

Exploring Hydration Energy

Hydration energy plays a crucial role in the solubility of ionic compounds. It is the energy released when ions interact with water molecules. This energy comes into play when a compound dissolves, and ions are surrounded by water molecules, which stabilize the ions that are separated from the lattice.
When the hydration energy of a compound is greater than its lattice energy, the ions are sufficiently stabilized, and the compound will dissolve. Sodium sulphate is a good example, where the hydration energy outweighs the lattice energy. This makes the dissolution process energetically favorable, leading to its high solubility in water.
Thus, hydration energy can be considered a driving force in the solubility of salts, as it can overcome the attraction within the crystal lattice when significant enough.

Ionic Compounds and Their Solubility

Solubility of ionic compounds in water is fundamentally determined by the competition between lattice energy and hydration energy. A salt or ionic compound is considered soluble if its hydration energy exceeds its lattice energy.
When we consider sodium sulphate and barium sulphate, we observe different solubility behaviors. Sodium sulphate dissolves readily in water because the energy released from hydration surpasses the energy required to break the ionic bonds in the lattice. Conversely, barium sulphate is sparingly soluble, as its high lattice energy is not sufficiently overcome by the hydration energy.

• Soluble compounds: Hydration energy > Lattice energy
• Sparingly soluble compounds: Lattice energy > Hydration energy
• Critical roles: Both energies dictate the solubility through their balance

Understanding this balance helps in predicting the solubility of various ionic compounds.