Question

How do you calculate the $pH$ of a buffered solution?

• A. By determining $Ka$, then using $Ka$ to determine the pH.
• B. By using the equation $Ka=\left[H3O^{+}\right]\left[X^{-}\right]/\left[HX\right]$
• C. By determining the $O{H}^{-}$ concentration.
• D. By using the equation $Ka=\left[H3O^{+}\right]\left[X^{-}\right]$
• E. By using the equation $Ka=\left[H{X}^{+}\right]\left[X^{-}\right]/\left[H3O^{+}\right]$

Answer 1

The correct option is B By using the equation $Ka=\left[H3O^{+}\right]\left[X^{-}\right]/\left[HX\right]$

You calculate the pH of a buffered solution by determining Ka, then using Ka to determine the pH.
The formula for the pH of acid buffer solution is $pH=pKa+log\frac{\left[X^{-}\right]}{\left[HX\right]}$
Also $pKa=-logKa$