From the data for each trial determine the pKa and calculate the Ka ofthe unknow
ID: 505402 • Letter: F
Question
From the data for each trial determine the pKa and calculate the Ka ofthe unknown acid. From the data for each trial, determine the pik and calculare the k,ofthe unknown acid. Trial 2 Trial 3 Titration of Unknown acid Trial 1 Mass of acid 207 Initial Volume of NaOH in burette 11.3 mL Volume of NaOH in burette at equivalence point Titration of Unknown acid Trial 2 Value Mass of acid Initial Volume of NaOH in burette 11.3 mL Initial pH 3.34 22.7 Volume of NaOH in burette at pH at equivalence point 11.16 Titration of Unknown acid Trial 3 Mass of acid 206 g Initial volume of NaOH in burette 28 mu. Initial pH 3.30 Volume of NaOH in burette at equivalence point pH at equivalence point 11.15 Analysis Analysis 1 Concentration of NaOH from trial 1 0.097 M correct correct Concentration of NaoH from triala2 0.09224 0.0971 Concentration of NaOH Solution AvertExplanation / Answer
Trial#2
moles NaOH used at equivalence point = 0.0971 M x 0.01116 L
= 1.084 x 10^-3 M
at equivalence point [OH-] added = [A-] formed = 1.084 x 10^-3 M
initial [HA] = [A-] formed = 1.084 x 10^-3 M
initial pH = 3.34
pH = -log[H+]
[H+] = 4.6 x 10^-4 M
fraction [H+] = fraction [A-] initially
Ka = [H+][A-]/[HA]
= (4.6 x 10^-4)^2/(1.084 x 10^-3)
= 1.95 x 10^-4
pKa = -log[Ka]
= -log(1.95 x 10^-4)
= 3.71
Trial#3
moles NaOH used at equivalence point = 0.0971 M x 0.01115 L
= 1.083 x 10^-3 M
at equivalence point [OH-] added = [A-] formed = 1.083 x 10^-3 M
initial [HA] = [A-] formed = 1.083 x 10^-3 M
initial pH = 3.30
pH = -log[H+]
[H+] = 5.0 x 10^-4 M
fraction [H+] = fraction [A-] initially
Ka = [H+][A-]/[HA]
= (5.0 x 10^-4)^2/(1.083 x 10^-3)
= 2.31 x 10^-4
pKa = -log[Ka]
= -log(2.31 x 10^-4)
= 3.64
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