HA(aq)+ H2O (l) <-> H3O+(aq)+ A¯ (aq)
Given the reaction above, which of the following will cause an increase in the pH of an equilibrium mixture? Give all answers which apply.
A) add KA B) add HA
C) remove A¯ D) remove HA
E) none of these will affect the pH.
Answer A and D ??
Yes, you are correct. Adding KA (potassium acetate) to the equilibrium mixture will cause an increase in the pH. This is because KA acts as a base and will consume some of the H3O+ ions, thereby increasing the concentration of OH- ions and shifting the equilibrium towards a higher pH.
On the other hand, removing HA (acetic acid) from the equilibrium mixture will also cause an increase in the pH. This is because HA is the acidic component in the reaction, and removing it will shift the equilibrium towards the basic side, increasing the concentration of OH- ions and raising the pH.
To determine which actions will cause an increase in the pH of the equilibrium mixture, we need to understand how each action affects the concentrations of H3O+ and OH- ions, which are responsible for defining the pH.
Let's analyze each answer choice:
A) Adding KA: Adding KA will have no effect on the pH. KA is a salt composed of the conjugate base (A¯) and its corresponding cation (K+). Since KA does not contain a hydrogen ion (H+), it does not directly contribute to the concentration of H3O+ ions. Therefore, the pH remains unchanged. So, answer choice A is incorrect.
B) Adding HA: Adding HA will increase the concentration of the weak acid in the system. According to Le Chatelier's principle, when additional HA is added, the equilibrium will shift to the left to relieve the stress. As a result, the concentration of H3O+ ions will decrease, leading to an increase in pH. So, answer choice B is correct.
C) Removing A¯: Removing A¯ will have no effect on the pH. The presence or absence of A¯ has no direct impact on the concentration of H3O+ ions. Consequently, the pH remains unchanged. So, answer choice C is incorrect.
D) Removing HA: Removing HA will decrease the concentration of the weak acid present. Once again, according to Le Chatelier's principle, the equilibrium will shift to the left to compensate for the loss of HA. As a result, the concentration of H3O+ ions will decrease, leading to an increase in pH. So, answer choice D is correct.
E) None of these will affect the pH: This answer choice is incorrect because adding HA or removing HA will indeed cause an increase in the pH.
Based on the analysis, the correct answer choices are B (add HA) and D (remove HA).