Asked by Delilah
What is the pH of a 0.02M solution of potassium benzoate solution ( K+ -OOCC6H5). The pka of benzoic acid is 4.19. (Write answer to the hundredths place)
Answers
Answered by
DrBob222
Let's call benzoic acid HBz so potassium benzoate is KBz. It is the Bz^- that is hydrolyzed and the pH is determined by that hydrolysis.
................Bz^- + HOH ==> HBz + OH^-
I..............0.02M.....................0.............0
C..............-x...........................x..............x
E..............0.02-x....................x...............x
Kb for Bz^- = (Kw/Ka for HBz) = (HBz)(OH^-)/(Bz^-)
Plug in Kw, Ka(from pKa), the E line for HBz, OH^-, Bz^- and solve for x = (OH^-) and convert to pH. Post your work if you get stuck.
................Bz^- + HOH ==> HBz + OH^-
I..............0.02M.....................0.............0
C..............-x...........................x..............x
E..............0.02-x....................x...............x
Kb for Bz^- = (Kw/Ka for HBz) = (HBz)(OH^-)/(Bz^-)
Plug in Kw, Ka(from pKa), the E line for HBz, OH^-, Bz^- and solve for x = (OH^-) and convert to pH. Post your work if you get stuck.
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