Question

If ‘S’ is solubility in mol dm^–3 and Ksp is the solubility product, then write the relation between them for CaF₂ and BaSO₄. Calculate the concentration of H₃O⁺ ion in soft drink whose pH is 3.5.

Answer 1

\[\ce{CaF_{2(s)} <=> Ca^{2+}_{ (aq)} + 2F^-_{ (aq)}}\]

x = 1, y = 2

∴ K_sp = x^x y^y S^x+y = (1)¹ (2)² S¹⁺² = 4S³

\[\ce{BaSO_{4(s)} <=> Ba^{2+}_{ (aq)} + SO^2-_{ 4(aq)}}\]

x = 1, y = 1

∴ K_sp = x^x y^y S^x+y = (1)¹ (1)² S¹⁺¹ = S²

Given: pH of soft drink = 3.5

To find: Concentration of H₃O⁺ ion

Formula: pH = − log₁₀[H₃O⁺]

Calculation: From the formula,

pH = −log₁₀[H₃O⁺]

∴ log₁₀[H₃O⁺] = - 3.5

= - 3 - 0.5 + 1 - 1

= (- 3 - 1) + 1 - 0.5

= - 4 + 0.5

= - 3.5

∴ [H₃O⁺] = Antilog₁₀ -3.5

= 3.162 × 10^-4 M

The concentration of H₃O⁺ ion in soft drink is 3.162 × 10⁻⁴ M.