Consider the equilibrium B(aq) + H₂O(l) ⇌ HB⁺(aq) + OH^–(aq). Suppose that a salt of HB⁺(aq) is added to a solution of B(aq) at equilibrium. (c) Will the pH of the solution increase, decrease, or stay the same?

Verified step by step guidance

1. Step 1: Understand the equilibrium reaction. The reaction B1aq2 + H2O1l2 Δ HB+1aq2 + OH-1aq2 is an acid-base reaction where B1aq2 acts as a base and H2O1l2 acts as an acid. The products are the conjugate acid HB+1aq2 and the conjugate base OH-1aq2.
2. Step 2: Identify the change in the system. The problem states that a salt of HB+1aq2 is added to the solution. This means that the concentration of HB+1aq2 in the solution increases.
3. Step 3: Apply Le Chatelier's Principle. According to Le Chatelier's Principle, when a change is applied to a system at equilibrium, the system will shift to counteract that change. In this case, the increase in HB+1aq2 will cause the equilibrium to shift to the left to reduce the concentration of HB+1aq2.
4. Step 4: Determine the effect on OH-1aq2. As the equilibrium shifts to the left, the concentration of OH-1aq2 will decrease because it is a product of the reaction and the reaction is moving in the reverse direction.
5. Step 5: Relate the change in OH-1aq2 to pH. The pH of a solution is related to the concentration of OH-1aq2 in the solution. As the concentration of OH-1aq2 decreases, the pH of the solution will also decrease. Therefore, the pH of the solution will decrease when a salt of HB+1aq2 is added to the solution.

Key Concepts

Le Chatelier's Principle

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system will adjust to counteract the change and restore a new equilibrium. In this case, adding a salt of HB+ will increase the concentration of HB+, shifting the equilibrium to the left to reduce the concentration of HB+ and OH-.

Acid-Base Equilibrium

Acid-base equilibrium involves the balance between acids and bases in a solution, which affects the pH. In this equilibrium, HB+ acts as an acid, donating protons (H+) to the solution, while B- acts as a base. The addition of HB+ will influence the concentration of H+ ions, thereby affecting the pH.

pH Scale

The pH scale measures the acidity or basicity of a solution, ranging from 0 (very acidic) to 14 (very basic), with 7 being neutral. A decrease in pH indicates an increase in H+ concentration, while an increase in pH indicates a decrease in H+ concentration. Understanding how the addition of HB+ affects H+ concentration is crucial for predicting changes in pH.