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

May 30, 2017

$12.00$

#### Explanation:

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

To calculate the $\text{pH}$ of a solution from a known $\left[{\text{H}}^{+}\right]$, we can use the formula

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

That is, the $\text{pH}$ 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 $\left[{\text{H}}^{+}\right]$ is equal to the number of decimal places of the $\text{pH}$, so the $\text{pH}$ is $12.00$.