Specific conductance of 0.03M of solution of weak base BoH is 1.5×10^-...
Solution:
Given:
Concentration of weak base, [BoH] = 0.03 M
Specific conductance, κ = 1.5 × 10^-4 S cm^-1
Molar conductance at infinite dilution, λ° = 250 S cm^2 mol^-1
To find:
Ionization constant of weak base, Kb
pH of the solution
Calculation:
1. Calculation of molar conductance, λm
Molar conductance, λm = κ / [BoH]
λm = 1.5 × 10^-4 / 0.03
λm = 5 × 10^-3 S cm^2 mol^-1
2. Calculation of degree of dissociation, α
The degree of dissociation of a weak base is given by the formula:
α = λm / λ°
Substituting the given values, we get:
α = 5 × 10^-3 / 250
α = 2 × 10^-5
3. Calculation of concentration of OH- ions, [OH^-]
Since the weak base BoH dissociates in water as:
BoH + H2O ⇌ Bo^- + H3O^+
We can write the equilibrium constant, Kb as:
Kb = [Bo^-] [H3O^+] / [BoH]
At equilibrium, the concentration of [Bo^-] and [BoH] are approximately equal. Therefore, we can write:
Kb = [H3O^+] α^2 / (1 - α)
Substituting the given values, we get:
Kb = [H3O^+] (2 × 10^-5)^2 / (1 - 2 × 10^-5)
4. Calculation of pH
The concentration of [H3O^+] can be calculated using the formula:
pH = -log [H3O^+]
Substituting the value of [H3O^+] in the above equation, we get:
pH = -log (Kb (1 - α) / α^2)
Substituting the values, we get:
pH = -log [(Kb (1 - 2 × 10^-5) / (2 × 10^-5)^2]
pH = 10.27
Therefore, the ionization constant of the weak base BoH is 5.5 × 10^-8 and the pH of the solution is 10.27.
Explanation:
In this problem, we are given the specific conductance of a solution of weak base BoH and we are asked to find out the ionization constant of the weak base and the pH of the solution.
The specific conductance of a solution is the conductance of a solution of unit volume and unit concentration. It is a measure of the ability of the solution to conduct electricity. The molar conductance of a solution is the conductance of a solution of unit volume and molar concentration.
The molar conductance of a weak electrolyte increases as the dilution of the solution increases. At infinite dilution, the molar conductance of a weak electrolyte becomes equal to the sum of the molar conductances of its ions. Therefore, the molar conductance at infinite dilution, λ°, is a measure of the maximum conductivity of a