# Question ab4a2

May 8, 2016

$\text{pH} = 4.77$

#### Explanation:

The pH of a solution is nothing more than a measure of its concentration of hydrogen ions, ${\text{H}}^{+}$, which you'll sometimes see referred to as hydronium cations, ${\text{H"_3"O}}^{+}$.

More specifically, the pH of a solution is calculated by taking the negative log base $10$ of the concentration of hydrogen ions

color(blue)(|bar(ul(color(white)(a/a)"pH" = - log(["H"^(+)])color(white)(a/a)|)))

The problem already provides you with the concentration of hydrogen ions, so plug this into the equation to find

$\text{pH} = - \log \left(1.7 \cdot {10}^{- 5}\right) = \textcolor{g r e e n}{| \overline{\underline{\textcolor{w h i t e}{\frac{a}{a}} 4.77 \textcolor{w h i t e}{\frac{a}{a}} |}}}$

Notice that because the pH is calculated using a negative log, a higher concentration of hydrogen ions will result in a lower pH.

In fact, the pH of pure water at room temperature is equal to $7$ because pure water has

["H"^(+)]_"pure water" = 1.0 * 10^(-7)"M" " "# and $\text{ "["OH"^(-)]_"pure water" = 1.0 * 10^(-7)"M}$

Your solution has a higher concentration of hydrogen ions, which is why the pH if lower than $7$. This corresponds to an acidic solution.