Another one in Aq. Equilibria..Not my chapter

Question

Consider an acid, HA, with pKa = 8.45. What is the pH of a buffer solution made up by mixing a 1.169M solution of the acid with an equal volume of a 1.566M solution of its salt?

Answer 1

it looks like they want you to use the Henderson–Hasselbalch equation

http://en.wikipedia.org/wiki/Henderson_h...

pH = pKa +  log [(anion)/ (acid)]

the bit about the "equal volumes, is to tell you that the concentrations have been diluted in half to:

0.5845 Molar acid  & 0.783 Molar anion from the salt, (not that it really matters in this calculaton)

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pH = pKa +  log [(anion)/ (acid)]

pH = 8.45  +  log [(0.783)/ (0.5845)]

pH = 8.45  +  log [1.3396]

pH = 8.45  +  0.127

pH = 8.577

your answer is: 8.58