Question

The secondary valency and the number of hydrogen bonded water molecule(s) in CuSO₄·5H₂O, respectively, are :

• A. 4 and 1
• B. 6 and 4
• C. 5 and 1
• D. 6 and 5

Hint:

In \(CuSO_4 \cdot 5H_2O\), only four water molecules are ligands; the fifth sits in the crystal lattice.

Answer 1

The Correct Option is A

Step 1: Blue vitriol is better represented as \([Cu(H_2O)_4]SO_4 \cdot H_2O\).
Step 2: The secondary valency is the coordination number of the central metal. Here, 4 water molecules are directly coordinated to the \(Cu^{2+}\) ion. So, secondary valency = 4.
Step 3: The 5th water molecule is held by hydrogen bonds between the sulfate ion and the coordinated water molecules. Thus, 1 water molecule is hydrogen bonded.