As 0.1 M HCl is added to 0.1 M KOH, the pH of the basic solution

• A. Decreases and the basicity decreases
• B. Increases and the acidity increases
• C. Decreases and the acidity decreases
• D. Increases and the basicity increases

Answer: (A)

Neutralization of a strong acid by a strong base drives the solution toward less basic conditions. When 0.1 M HCl is added to 0.1 M KOH, each mole of HCl reacts with a mole of OH− to form water, removing hydroxide ions from the solution. Because the base’s defining species (OH−) is being consumed, the solution loses its basic character, and the pH drops. If the amounts are equal, you approach a neutral solution around pH 7; with less base left, it stays basic but weaker, and with excess acid, it becomes acidic and pH continues to fall. So the pH decreases and the basicity decreases as acid is added.