When chemists are using compounds as catalysts, sometimes only a very low concentration is needed. Suppose you are using 8.0 * 10^–8 m HCl(aq) as a catalyst for an organic reaction and you are using a pH meter to gauge its acidity. What pH value should you expect?

ANTICIPATE Although the acid is very dilute, it is an acid, and you should expect a pH of slightly less than 7.

PLAN Let [HCl]_initial = 8.0 * 10^–8 mol · L^–1 and [H₃O⁺] = x; substitute these values into Eq. 1 and solve for x.

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[H30+] - [HC] initial[H30+] - Kw = 0 (1)