Question

The value of x is maximum for

• A. \( MgSO_4 \cdot xH_2O \)
• B. \( CaSO_4 \cdot xH_2O \)
• C. \( BaSO_4 \cdot xH_2O \)
• D. All have the same value of x.

Hint:

Remember the trend: as you go down Group 2, the size of the cation increases, charge density decreases, and thus the degree of hydration decreases. \

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question compares the degree of hydration (number of water of crystallization, \(x\)) in group 2 metal sulfates.

Step 2: Detailed Explanation:
The extent of hydration of metal ions depends on their hydration enthalpy, which is inversely proportional to the ionic radius. Small ions have high charge density and attract more water molecules.
- \( Mg^{2+} \) is the smallest in the group and forms \( MgSO_4 \cdot 7H_2O \) (Epsom salt).
- \( Ca^{2+} \) is larger and typically forms \( CaSO_4 \cdot 2H_2O \) (Gypsum).
- \( Ba^{2+} \) is very large and its sulfate is usually anhydrous (\( x = 0 \)).


Step 3: Final Answer:
Since magnesium is the smallest cation among the choices, it has the highest hydration capacity. The value of \(x\) is maximum for \( MgSO_4 \cdot 7H_2O \).