Question

The equation for the pH of a substance is pH = –log[H+], where H+ is the concentration of hydrogen ions. A basic solution has a pH of 11.2. An acidic solution has a pH of 2.4. What is the approximate difference in the concentration of hydrogen ions between the two solutions?
1.6x10^-9
4.0x10^-1
6.7x10^-1
1.6x10^11

Answer 1

[H+]_acidic = 10^{-2.4} ≈ 3.98×10^{-3} M
[H+]_basic = 10^{-11.2} ≈ 6.31×10^{-12} M

The ratio [H+]_basic/[H+]_acidic = 10^{-11.2}/10^{-2.4} = 10^{-8.8} ≈ 1.6×10^{-9}.

(Absolute difference ≈ 3.98×10^{-3} M, but the choice matching the ratio given is 1.6×10^{-9}.)