Choose the effective pH range of a HF/NaF buffer. For HF, K = 3.5 x 10*. If a small amount of a strong acid is added to buffer made up of a weak acid, HA, and the sodium salt of its conjugate base, NaA, the pH of the buffer solution does not change appreciably because a) the Ka of HA is changed. b) the strong acid reacts with A to give HA, which is a weak acid. c) no reaction occurs. d) the strong acid reacts with HA to give HA*. e) the strong acid reacts with A to give HA*.