The pH of a 0.124 M solution of a weak base is 10.89 at 25°C. Calculate the pH of a 0.0470 M solution of the base at 25°C.
A) 10.68
B) 11.31
C) 4.13
D) 3.32
E) 10.47

Question

Quizplus · Accepted Answer

The pH of a solution of a weak base depends on its concentration and its base dissociation constant (Kb). When the concentration of the base decreases, the pH decreases but not linearly due to the logarithmic nature of the pH scale. Given the pH of the more concentrated solution, we can infer that the base is relatively weak since its pH is significantly above 7 but not extremely high. As the concentration of the base decreases from 0.124 M to 0.0470 M, the pH will decrease because there are fewer base molecules to accept protons, leading to a lower level of ionization and thus a lower pH. However, without the exact value of Kb, we cannot calculate the exact pH change mathematically here. The closest reasonable estimate given the options and understanding that the pH will decrease but not drastically is 10.68.

The PH of a 0