Solubility of calcium phosphate (molecular mass, M) in water is W_g per 100 mL at 25° C. Its solubility product at 25° C will be approximately.

Solution

Chemistry ma’am · 3 steps

Convert W g per 100 mL into mol per litre first, then use the 3 : 2 ion ratio to build Ksp.

1. Molar solubility. W g in 100 mL means 10W g in 1 L. Dividing by the molar mass gives s = 10W/M mol L⁻¹.
2. Ions released. Ca₃(PO₄)₂ ⇌ 3Ca²⁺ + 2PO₄³⁻. So [Ca²⁺] = 3s and [PO₄³⁻] = 2s.

   Kₛₚ = (3s)³(2s)² = 108 s⁵ = 108 × 10⁵(W/M)⁵

3. So. Kₛₚ = 1.08 × 10⁷(W/M)⁵ ≈ 10⁷(W/M)⁵, which is option (c).

The idea to keep. For AₓB_y, Kₛₚ = xˣ yʸ sˣ⁺ʸ, and s must be in mol per litre. Fix the units before you raise anything to a power.

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