All courses › Chemistry 2 › A buffer when the ratio is ten

A buffer when the ratio is ten

The logarithm in the buffer equation is zero when base and acid are equal, and it is 1 when the base is ten times as concentrated as the acid. The pH then moves by exactly one unit from pKa. It is useful to know these two special cases without a calculator. Outside the range from one tenth to ten times, the buffer is poor, because one partner is almost used up. A buffer with acetic acid therefore stays in the acidic range, around 4 to 6, not at pH 7.

Symbols

Example

Acetic acid, pKa 4.76. Equal amounts: $\mathrm{pH} = 4.76 + \lg 1 = 4.76$.

Ten times more base: $\mathrm{pH} = 4.76 + \lg 10 = 5.76$.

← The buffer equation · Titration →

Part of Chemistry 2: Buffers and titration.