How do you solve chemistry buffer problems?

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How do you solve chemistry buffer problems?

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Answer 1 · 2016-08-18T07:51:10

$p H = p K_{a} + {log}_{10} {\frac{[A^{-}]}{[H A]}}$ $pH=pK_a + log_10{[[A^-]]/[[HA])}$

Explanation:

See this [old answer.](https://socratic.org/questions/how-do-buffers-maintain-ph).

As you have probably heard ad nauseaum, at the point of half equivalence in the titration weak acid with a strong base, $[A^{-}] = [H A]$ $[A^-]=[HA]$ , and the expression ${log}_{10} {\frac{[A^{-}]}{[H A]}}$ $log_10{[[A^-]]/[[HA])}$ $=$ $=$ ${log}_{10} (1) = 0$ $log_10(1)=0$ .

Going back to the equation, this means that $p H = p K_{a}$ $pH=pK_a$ at the point of half equivalence in a strong base/weak acid or strong acid/weak base titration.

Problems are usually composed so that the formation of a buffer is not immediately obvious. For example, we may start with some concentration of say, acetic acid, $H O A c$ $HOAc$ , and $\frac{1}{2}$ $1/2$ an equiv of sodium hydroxide is added. If the $p K_{a}$ $pK_a$ of acetic acid $=$ $=$ $4.76$ $4.76$ (which it does), then what is the $p H$ $pH$ of the given buffer?

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How do you solve chemistry buffer problems?

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