Determine the mass (in g) of sodium butanoate
(NaC3H7COO) that must be added to 78.9 mL of
0.609 M butanoic acid to yield a pH of 6.43. Report your answer to
3 significant figures.
Assume the volume of the solution does not change and that the 5%
approximation is valid.
http://chemresources.chemistry.dal.ca/firstyear/acid_base.html
pH = 6.43
pKa = 4.824
moles of butanoic acid = 78.9 x 0.609 / 1000
= 0.04805 mol
pH = pKa + log [salt / acid]
6.43 = 4.824 + log [NaC3H7COO / 0.04805]
NaC3H7COO = 1.94
moles of NaC3H7COO = 1.94
mass of NaC3H7COO = 1.94 x 110.1
mass of NaC3H7COO = 213 g
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