Question

Calculate the hydronium ion concentration in an aqueous solution with a pH of 11.7 at
25°C.

Answer 1

Approximately
`2* 10^(-12)\;\rm mol \cdot L^(-1)`.

Step-by-step explanation:

The hydronium ion concentration
`\left[\mathrm{H_3O^(+)}\right]` of an aqueous solution can be found from its
`\rm pH` with the equation:

`\displaystyle \left[\mathrm{H_3O^(+)}\right] = 10^{-\mathrm{pH}}`.

For this solution,
`\rm pH= 11.7`. Hence,

`\begin{aligned}& \left[\mathrm{H_3O^(+)}\right] \\ &= 10^{-\mathrm{pH}} \\ &= 10^(-11.7) \approx 2 * 10^(-12)\end{aligned}`.

Note that for this equation, the number of significant figures in
`\left[\mathrm{H_3O^(+)}\right]` should be the same as the number of decimal places in
`\rm pH`. For example, the
`\rm pH` of this question comes with only one decimal place. As a result, there would be only one significant figure in the
`\left[\mathrm{H_3O^(+)}\right]` obtained from the equation.