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

Solution

Chemistry ma’am · 4 steps

Rewrite the formula as [Cu(H₂O)₄]SO₄.H₂O: four waters bind copper, and one is only held by H-bonds.

1. Real structure. Of the five water molecules in blue vitriol, four are attached directly to Cu²⁺ as ligands. The fifth is not bonded to copper at all. So the formula is better written as [Cu(H₂O)₄]SO₄.H₂O.
2. Secondary valency. In Werner's theory, the secondary valency is the coordination number: the number of ligands bound directly to the metal. The four coordinated waters give Cu²⁺ a secondary valency of 4, arranged in a square plane.
3. The fifth water. The fifth water sits outside the coordination sphere. It is held in the crystal only by hydrogen bonds to the oxygens of SO₄²⁻ and to the coordinated waters. That gives 1 hydrogen-bonded water.
4. So. The secondary valency is 4 and one water is hydrogen bonded, which is option (b).

The idea to keep. Water of crystallisation is not always a ligand. Ask which molecules bind the metal directly; only those count toward the secondary valency, and the rest are held in the lattice.

Answer from the NTA final answer key. Solution by PrepWiser.