Which one of the following alkaline earth metal sulphates has its hydration enthalpy greater than its lattice enthalpy?

Options

A. `BeSO_(4)`
B. `BaSO_(4)`
C. `SrSO_(4)`
D. `CaSO_(4)`

Answer

To solve the question of which alkaline earth metal sulfate has its hydration enthalpy greater than its lattice enthalpy, we can follow these steps:

### Step 1: Understand the Concepts
- **Hydration Enthalpy**: This is the energy released when one mole of ions is surrounded by water molecules. It is related to the solubility of the compound in water.
- **Lattice Enthalpy**: This is the energy required to separate one mole of a solid ionic compound into its gaseous ions. It is influenced by the size and charge of the ions involved.

### Step 2: Identify the Alkaline Earth Metals
The alkaline earth metals include:
- Beryllium (Be)
- Magnesium (Mg)
- Calcium (Ca)
- Strontium (Sr)
- Barium (Ba)
- Radium (Ra)

### Step 3: Analyze the Trend in Group 2
As we move down the group from Beryllium to Barium:
- The size of the metal ions increases.
- The hydration enthalpy generally decreases because larger ions are less effectively solvated by water.
- The lattice enthalpy generally increases because smaller ions can pack more closely together, leading to stronger ionic bonds.

### Step 4: Compare the Sulfates
We need to consider the sulfates of these metals:
- Beryllium sulfate (BeSO₄)
- Magnesium sulfate (MgSO₄)
- Calcium sulfate (CaSO₄)
- Strontium sulfate (SrSO₄)
- Barium sulfate (BaSO₄)

### Step 5: Determine Hydration and Lattice Enthalpy
- **Beryllium Sulfate (BeSO₄)**:
- Small size of Be²⁺ leads to high hydration enthalpy.
- Lattice enthalpy is lower due to the small size of the ions.

- **Barium Sulfate (BaSO₄)**:
- Larger size of Ba²⁺ leads to lower hydration enthalpy.
- Lattice enthalpy is higher due to the larger size of the ions.

### Step 6: Conclusion
From the analysis, Beryllium sulfate (BeSO₄) has a higher hydration enthalpy compared to its lattice enthalpy because:
- The small size of Be²⁺ allows for significant interaction with water, leading to high hydration enthalpy.
- The lattice enthalpy is lower due to the small size of the ions, making it easier to separate them.

### Final Answer
Thus, the alkaline earth metal sulfate that has its hydration enthalpy greater than its lattice enthalpy is **Beryllium sulfate (BeSO₄)**.

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