Correct Answer - Option 1 : 1.08 × 10
-13
Concept:
- The solubility product of sparingly soluble salt in a saturated solution can be defined as the product of the equilibrium molar concentration of its constituent ions raised to the power of their stoichiometric coefficient.
- What happens is that in a sparingly soluble salt, such as BaSO4, the salts are not completely ionised and there exists an equilibrium between the ions and undissociated insoluble salt. At equilibrium, the equilibrium constant is known as the solubility product constant or simply solubility product.
Let us take a general salt AxBy. In the equilibrium, the dissociation may be represented as:
AxBy = xAy+ + yBx-, where x and y are stoichiometric coefficients.
- The generalised solubility product 'Ksp' is:
Ksp = [Ay+]x[Bx-]y
- The Ksp of a slightly soluble salt is constant for a given temperature, irrespective of the source of ion in the Ksp expression.
- Solubility is defined as the number of moles of solute present in a litre of a saturated solution at a given temperature. It is denoted by 'S'.
- The solubility of a substance at a given temperature is not constant and depends on the presence of other ions.
- The salt AxBy dissociates as xAy+ + yBx-, if the solubility of The salt is 'S', the 'xS' amount of ion Ay+is produced and 'yS' amount of ion Bx- is produced.
- In solubility product expression, the concentration terms are thus the solubility values of the ions.
Ksp = [xS]x[yS]y
Calculation:
Given:
- The solubility of a salt A2B3 is 1 × 10-3.
- The salt will dissociate as follows:
A2B3 = 2A3+ + 3B2-
- The Ksp value will be given by: [A3+]2[B2-]3
- The solubility 'S' of the ions is = 1 × 10-3.
Hence, Ksp value =
Ksp = [xS]x[yS]y
Ksp = [2s]2[3s]3 = 108 [s]5 = 108 × [1 × 10-3]5
So, Ksp = 108 × 1 × 10-15 = 1.08 × 10-13
Hence, solubility product is 1.08 × 10-13.
