Question

Ca\(^{2+}\) + Na\(_6\)(PO\(_3\))\(_6\) → X + yNa\(^+\). Identify X

• A. \([Na_2Ca(PO_3)_6]^{2-}\)
• B. \([Ca_2(PO_3)_6]^{2-}\)
• C. \([Na_4Ca(PO_3)_6]\)
• D. \([Ca_3(PO_3)_6]\)

Hint:

In complex salts, multivalent ions like \(Ca^{2+}\) often replace two monovalent ions like \(Na^+\).

Answer 1

The Correct Option is A

Step 1: Nature of Na₆(PO₃)₆.
It is a complex salt where Na⁺ balances the polyphosphate anion (PO₃)₆⁶⁻.

Step 2: Calcium substitution.
Ca²⁺, with higher charge density, displaces Na⁺ ions; one Ca²⁺ replaces two Na⁺.

Step 3: Charge balance in the mixed complex.
Partial replacement yields a complex retaining some Na⁺, with the formula [Na₂Ca(PO₃)₆]²⁻.

Step 4: Coordination rationale.
Calcium coordinates with the phosphate chain while residual sodium remains as counterions.

Step 5: Conclusion.
The complex ion formed is [Na₂Ca(PO₃)₆]²⁻.