Question

The concentration of H+ ions in a solution is `1.0 xx 10^-12` M. What is the pH of the solution?

Answer 1

`12.00`

Explanation:

We're asked to calculate the `"pH"` of a solution with a known hydrogen (hydronium) ion concentration (`["H"^+]` or `["H"_3"O"^+]`; they both represent the same thing in this case).

To calculate the `"pH"` of a solution from a known `["H"^+]`, we can use the formula

`"pH" = -log["H"^+]`

That is, the `"pH"` of a solution is the negative of the logarithm of the hydronium/hydrogen ion concentration.

Using this formula, we have

`"pH" = -log(1.0 xx 10^-12M) = color(red)(12.00`

The number of significant figures in the `["H"^+]` is equal to the number of decimal places of the `"pH"`, so the `"pH"` is `12.00`.