Question

If the Kb�b of a weak base is 3.9×10−6,3.9×10−6, what is the pH

of a 0.23 M0.23 M solution of this base?
pH=

Answer 1

To calculate the pH of a 0.23 M solution of a weak base with a Kb of 3.9×10⁻¶, we first determine the [OH⁻], then the pOH, and use this to find the pH, which is approximately 8.56.

Step-by-step explanation:

The subject of this question is the calculation of the pH of a weak base solution in Chemistry. Given the Kb of a weak base as 3.9×10⁻¶ and the concentration of the base as 0.23 M, we can calculate the pH.

To find the pH, we must first determine the hydroxide ion ([OH⁻]) concentration using the formula Kb = [OH⁻]² / (initial concentration of weak base - [OH⁻]). Here we can assume that [OH⁻] is much less than the initial concentration of the base, simplifying this expression to Kb ≈ [OH⁻]² / initial concentration. Solving this equation gives us [OH⁻] which, after calculation, is approximately 1.4 × 10⁻³ M.

The pOH can then be calculated as pOH = -log([OH⁻]), which gives us a pOH of approximately 5.44. Finally, we convert pOH to pH using the relationship pH = 14 - pOH, resulting in a pH of approximately 8.56 for the solution.