Question

The equation for the pH of a substance is pH = –log[H+], where H+ is the concentration of hydrogen ions. Which equation models the concentration of hydrogen ions (H+) of a solution whose pH is 7.2?
[H+] = log7.2
[H+] = -log7.2
[H+] = 10^-7.2
[H+] = 10^7.2

Answer 1

Start with pH = −log10([H+]). If pH = 7.2 then −log10([H+]) = 7.2, so log10([H+]) = −7.2 and [H+] = 10^(−7.2).

(So the correct choice is [H+] = 10^-7.2 ≈ 6.31×10^-8 M.)