Alumina is insoluble in water because:

Options

A. It is a covalent compound
B. It has high lattice energy ad low heat of hydration
C. It has low lattice energy and high heat of hydration
D. `Al^(3+) and O^(2-)` ions are not excessively hydrated

Answer

To determine why alumina (Al₂O₃) is insoluble in water, we can analyze the properties of the compound and its ions. Here’s a step-by-step solution:

### Step 1: Understand the Composition of Alumina
Alumina is primarily composed of aluminum ions (Al³⁺) and oxide ions (O²⁻). It is an ionic compound.

**Hint:** Identify the ions that make up the compound and their charges.

### Step 2: Define Lattice Energy
Lattice energy is the energy released when gaseous ions combine to form an ionic solid. A high lattice energy indicates that the ions are held tightly together in the solid state, making it difficult for them to separate and dissolve in water.

**Hint:** Remember that lattice energy is a measure of the strength of the ionic bonds in the solid.

### Step 3: Define Heat of Hydration
Heat of hydration is the energy released when ions are surrounded by water molecules. A high heat of hydration means that the ions are stabilized by water molecules when dissolved.

**Hint:** Consider how water interacts with ions and the energy changes involved.

### Step 4: Compare Lattice Energy and Heat of Hydration
For a compound to be soluble in water, the energy released from hydration must be greater than the lattice energy. If the lattice energy is high and the heat of hydration is low, the compound will not dissolve.

**Hint:** Think about the balance between the energy required to break the ionic bonds and the energy released when ions are hydrated.

### Step 5: Analyze Alumina's Properties
In the case of alumina:
- It has a **high lattice energy** due to the strong attraction between the Al³⁺ and O²⁻ ions.
- It has a **low heat of hydration** because the small size of the Al³⁺ ion leads to a high charge density, but the overall hydration energy is not sufficient to overcome the strong lattice energy.

**Hint:** Consider the size and charge of the ions and how they affect hydration.

### Conclusion
Since alumina has high lattice energy and low heat of hydration, it is insoluble in water. Therefore, the correct answer is that alumina is insoluble in water because it has high lattice energy and low heat of hydration.

**Final Answer:** Alumina is insoluble in water because it has high lattice energy and low heat of hydration.