Question

1. The molar solubility of magnesium carbonate in a 0.267 M ammonium carbonate solution is ______ M.

2. The molar solubility of silver phosphate in a 0.201 M silver nitrate solution is _____ M.

Answer 1

1) MgCO₃    Mg²⁺_(aq) + CO₃^2-_(aq)

let the solubility of MgCO₃ is S mol/L

Thus, [Mg²⁺] = [CO₃^2-] = S mol/L

Ammonium carbonate is a strong electrolyte which dissociates as,

(NH₄)₂CO₃ 2NH₄⁺_(aq) +  CO₃^2-

Thus, [CO₃^2-] = 0.267 M

Hence, overall [CO₃^2-] = ( S + 0.267 ) M or mol/L

Ksp = [Mg²⁺] [CO₃^2-]

= S (S + 0.267)

or, 3.5 x 10^-8 = S (S + 0.267) = S² + 0.267 S

owing to the very small Ksp vale, S² can be neglected

or, 3.5 x 10^-8 =  0.267 S

or, S = 1.31 x 10^-7 mol/L

Hence, the solubility of MgCO₃ is 1.31 x 10^-7 mol/L