Can anyone calculate the pH of a buffer solution produced by?
The original solution contains 0.01 mole of ethanoic acid (acetic acid). It may be assumed that only a small fraction of this is dissociated. 3.28 g of sodium ethanoate is equivalent to 3.28/82 = 0.04 mole Na(CH3COO). This is almost completely dissociated in solution into Na+ and the conjugate base CH3COO-. From the figure given, the pKa of ethanoic acid is 4.735. Using the Henderson-Hasselbalck equation, the pH of the resulting solution will be pH = PKa + log([CH3COO-]/[CH3COOH]) = 4.735 + log(0.04/0.01) = 5.337 The effect of adding HCl to the mixture is to convert some of the sodium ethanoate to ethanoic acid. 10 ml of 0.1 M HCl contains 0.001 mole HCl, and hence the concentration of ethanoate ions is reduced by this amount, and the concentration of ethanoic acid increased by the same. The Henderson-Hasselbalck equation becomes pH = pKa + log(0.039/0.011) = 4.735 + 0.550 = 5.285 that is, the HCl produces a small reduction in the pH of the buffer.
