Question

What is the pH of a 0.01 M solution of the strong acid `HClO_4`, perchloric acid?

Answer 1

`pH=-log_(10)[H_3O^+]=-log_(10)(10^-2) = 2`

Explanation:

This question may be answered without a calculator. We are asked to take the logarithm to the `"base 10"` of `10^(-2)`, which is clearly `-2`, why? We are then asked to give the negative value of that logarithm.

Perchloric acid is exceptionally strong, and undergoes complete ionization in water:

`HClO_4(aq) + H_2O(aq) rarr H_3O^+ + ClO_4^-`

Now not only do you have to learn how to take logarithms, you also have to learn how to take antilogarithms, if asked to find concentrations given a `pH`, see here .