Which would decrease the pH of of a solution of hydrochloric acid? The addition of — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

Decreasing the pH requires increasing the concentration of $[\text{H}^+]$. The initial solution has $[\text{H}^+] = 0.01\text{ M}$. Adding a stronger acidic solution (0.02 M HCl) will increase the overall $[\text{H}^+]$ of the mixture, thereby lowering the pH. Adding a weaker acid (0.005 M HCl) or water will dilute the existing $0.01\text{ M}$ acid, raising the pH. Adding magnesium metal consumes $\text{H}^+$ to release $\text{H}_2$ gas, which also raises the pH. Therefore, correct answer is B.