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Solubility from Ksp

C3L6 · UKChO Round 1 · IChO · unreviewed

Ksp = (xs)^x(ys)^y = x^x y^y s^(x+y).

Practise this with fresh numbers

Worked example

Ksp = 8.0 × 10⁻⁹ for a sparingly soluble salt MₓXᵧ (x = 2, y = 2). What is s?

1. Ksp and solubility (MₓAᵧ): solve for s
$s = \left(\dfrac{K_\mathrm{sp}}{x^x y^y}\right)^{1/(x+y)}$
= 0.004729 mol dm⁻³

Answer: s = 0.00473 mol dm⁻³

Method

Ksp = (xs)^x(ys)^y = x^x y^y s^(x+y). Do not forget the x^x y^y factor (e.g. 4s³ for MX₂).

Formulas used

Ksp and solubility (MₓAᵧ)
$K_\mathrm{sp} = (xs)^x(ys)^y$

Practise this with fresh numbers

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