The pH of a buffer can be predicted using the Hendersen-Hasselbach equation:
pH=pKa+ log([conjugate base][conjugate acid])
The choice of the conjugate acid-base pair (as you did in the previous questions) determines the pKa value to be used in the H-H equation. By varying the relative amounts of conjugate acid and base, it is possible to adjust the pH value of the buffer solution to the desire value. The ratio of [A-]/[HA] is defined as the buffer ratio.
If 0.100 L of a buffer solution is prepared by mixing 0.30 mol of formic acid (pKa = 3.74) and 0.60 mol of sodium formate in water, what is the buffer ratio in the resulting solution?
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I don't understand why you have a problem? The question tells you the buffer ratio is (A^-)/(HA). It tells you (A^-) is 0.30 mol (0.3mol/0.1L = ? M) and it tells you (HA) is 0.6 mol (0.6mol/0.1L = ?). So 3/6 = ?
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