A saturated aqueous solution of sparingly soluble salt AB3has the vapo...
Given:
- Vapour pressure of the solvent (P°) = 17.33 mm
- Vapour pressure of the saturated solution (P) = 17.33 - 0.08 = 17.25 mm
Explanation:
The vapour pressure of a solution depends on the concentration of solute particles in the solution. In this case, the solute is a sparingly soluble salt AB3.
The solubility product (Ksp) of a sparingly soluble salt is a measure of its solubility in water. It is defined as the product of the concentrations of the ions in a saturated solution, each raised to the power of their stoichiometric coefficient.
The solubility product expression for AB3 can be written as:
AB3(s) ⇌ A3+(aq) + 3B-(aq)
The solubility product constant (Ksp) for AB3 can be given as:
Ksp = [A3+][B-]^3
Since AB3 is sparingly soluble, the concentration of AB3(s) in the saturated solution can be assumed to be constant. Therefore, the concentration of A3+ and B- ions in the saturated solution can be considered to be proportional to the vapour pressure of the solution.
Calculating the solubility product:
1. The vapour pressure of the saturated solution (P) is 17.25 mm.
2. The vapour pressure of the solvent (P°) is 17.33 mm.
3. The decrease in vapour pressure due to the presence of solute is given by:
ΔP = P° - P
= 17.33 - 17.25
= 0.08 mm
4. According to Raoult's law, the decrease in vapour pressure is directly proportional to the mole fraction of the solute particles in the solution.
ΔP ∝ x solute
5. Let the mole fraction of AB3(s) in the saturated solution be x. Then, the mole fraction of A3+ and B- ions can be assumed to be 3x and 3x, respectively.
ΔP ∝ x + 3x + 3x
ΔP ∝ 7x
6. Therefore, 7x = 0.08
x = 0.08/7
x = 0.0114
7. The concentration of A3+ and B- ions in the saturated solution can be assumed to be proportional to the mole fraction x.
[A3+] = 3x = 3(0.0114) = 0.0342
[B-] = 3x = 3(0.0114) = 0.0342
8. The solubility product (Ksp) can be calculated as the product of the concentrations of A3+ and B- ions.
Ksp = [A3+][B-]^3
= (0.0342)(0.0342)^3
= 0.0342 x 0.0342^3
= 0.0342 x 0.0000437
= 1.49 x 10^-6
Conclusion:
The solubility product (Ksp)