24) [H+]A = 500 x [H+]B
ΔpH = pHB - pHA
ΔpH = -log[H+]B - (-log[H+]A) = -log[H+]B + log[H+]A
ΔpH = -log([H+]B/[H+]A)
ΔpH = -log([H+]B/500 x [H+]B) = -log(500-1) = 2.70
Because [H+]A > [H+]B, the pH of solution A is 2.70 pH units lower than the pH of solution B.