In a solubility equilibrium, the

Rate of dissolving equals the rate of crystallization

Neither dissolving nor crystallization are occurring

Concentration of solute and solvent are always equal

Mass of dissolved solute is greater than the mass of the solution

pH Scale and Acidity - Periodic Variation of Acidic, Basic Properties

What Is Solubility?

Solubility is the amount of the substance (ionic or others) soluble to make a saturated solution at a specified temperature and in a fixed volume of solvent. Solubility changes with the nature of the substance, solvent, temperature and presence of common ions.

Sparingly soluble substances have very low solubility (AgCl, BaSO₄) in water. In spite of the low solubility, being ionic substances, they can be considered to form a saturated solution, and the ions are in equilibrium with the undissolved solid.

Read More: Solubility

\begin{array}{l} A g C l ⇌ A g^{+} C l^{-} \end{array}

(Undissolved ) (Dissolved)

Equilibrium constant of dissociation

\begin{array}{l} = K c = \frac{{[A g]}^{+} {[C l]}^{-}}{[A g C l]} \end{array}

Silver chloride being solid, the concentration is taken to be constant, such that a new equilibrium constant can be considered.

\begin{array}{l} Solubility Product = K s p = K c [A g C l] = [A g^{+}] [C l^{-}] \end{array}

= Product of the concentration of the ions.

For a sparingly insoluble salt of the general formula, AxBy

\begin{array}{l} A x B y (s) ⇌ x A^{y} (a q) + y B^{x} - (a q) \end{array}

\begin{array}{l} K s p = [x A^{y +}] [y B^{x -}]^{y} \end{array}

The value is constant for the substance and varies only with temperature.

Significance of Solubility Product

The presence of a common ion may affect the equilibrium and hence, the concentration (solubility) but not the solubility product.
Precipitation of the solutes occurs when the ionic product exceeds the Ksp.

Solubility Videos

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Relationship between Solubility and Solubility Product

\begin{array}{l} A x B y ⇌ x A^{Y +} + y B^{x -} \end{array}

At equilibrium C Cx Cy

Ksp = [xA^Y+ ]^x[yB^x-]^y = [Cx]^x [Cy]^y = [C]^x [x]^x [C]^y [y]^y

Ksp = [C]^x [C]^y [x]^x [y]^y = [C]^x+y [x]^x [y]^y

Ksp = [S]^x+y [x]^x [y]^y S is the solubility= C= mole/l

\begin{array}{l} Solubility = [S]^{x + y} = \frac{K s p}{x^{x} y^{y}} \end{array}

Example: For silver chromate,

\begin{array}{l} A g_{2} C r O_{4} ⇌ 2 A g^{+} + C r O_{4}^{2 -} \end{array}

Ksp = (2S)² S = 4S³

Also Read

Solubility and Solubility Product

What Is Solubility?

Significance of Solubility Product

Solubility Videos

Solubility – JEE Chemistry

Solubility and Henry’s Law

Relationship between Solubility and Solubility Product

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