Answer: The weak acid neutralises added base while the conjugate base neutralises added acid, keeping their ratio steady.
- A The conjugate base converts mainly into a strong base the moment any acid is added to it in the majority of documented cases
- B The mixture has a pH that stays fixed no matter how much acid or base is added to it as widely reported in standard reference material
- C The weak acid neutralises added base while the conjugate base neutralises added acid, keeping their ratio steady
- D The weak acid and conjugate base mostly evaporate before reacting with anything that is added later under most conditions studied
Correct answer: C. The weak acid neutralises added base while the conjugate base neutralises added acid, keeping their ratio steady
Explanation: In a buffer, the weak acid component reacts with added base and the conjugate base component reacts with added acid, so the ratio of conjugate base to weak acid changes only slightly and the pH stays nearly constant.
As the reaction proceeds, reactant concentration falls and product concentration rises until both level off at equilibrium.
Concept context
When forward and reverse reaction rates are equal, equilibrium is reached. Learn about Kc, Kp, Le Chatelier's principle, and acid-base equilibria, including pH, buffer solutions, and solubility product.