Home > Community > What is the pH of a buffer consisting of 0.700 M propionic acid (HC3H5O2, call it HA) and 0.650 M sodium propionate (NaC3H5O2, just call it NaA, with the anion being A)? The Ka for propionic acid is 1.31 x 10-5
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Oreld Hadilberg

What is the pH of a buffer consisting of 0.700 M propionic acid (HC3H5O2, call it HA) and 0.650 M sodium propionate (NaC3H5O2, just call it NaA, with the anion being A)? The Ka for propionic acid is 1.31 x 10-5

Diane Fiorito  Follow

Perhaps do your own homework?

These calculations assume that the acid does not dissociate, nor does the propanoate associate with H+ ions. One of these things Is it true true but statistically it makes no odds.

kA = [H+][A-]/[HA]

So, [H+] = Ka x [HA]/ [A-]

And pH = - log [H+]

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Andrei Tancau  Follow

Calculate poH using the Henderson - Hasselbalch equation

pH = pKa + log ([NaA] / [HA] )

pKa = - log 1.31*10^-5 = 4.88

pH = 4.88 + log ( 0.650 / 0.700 )

pH = 4.88 + log 0.928

pH = 4.88 + ( -0.032)

pH = 4.85

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