A 10.00-mL aliquot of 0.2000 M mercaptoacetic acid ( H SCH 2 CO 2 H ) is titrate
ID: 1063160 • Letter: A
Question
A 10.00-mL aliquot of 0.2000 M mercaptoacetic acid (HSCH2CO2H) is titrated with 0.1200 M KOH. Calculate the pH
a)after the addition of 0.00 mL KOH.
b)at the 1st equivalence point.
c)after the addition of 5.00 mL of KOH.
d)half-way between the initial point and the 1st equivalence point.
e)1.00 mL before you reach the 1st equivalence point.
f)after the addition of 2.00 mL of KOH past the 1st equivalence point.
g)at the 2nd equivalence point.
h)half-way between the 1st equivalence point and the 2nd equivalence point.
i)2.00 mL before you reach the 2nd equivalence point.
j)after the addition of 5.00 mL of KOH past the 2nd equivalence point.
Explanation / Answer
insert values into the Ka expression for mercaptoacetic acid .
The Ka for mercaptoacetic acid is =1.48x10-4
HSCH2CO2H -----> HSCH2CO2- + H+
1) at initial 0.00 ml KOH
Ka = [HSCH2CO2-] [H+] / [HSCH2CO2H]
1.48 x 10-4 = [ (X) (X) / [0.2M]
[H+] = 5.439 x 10-3 M
pH = -log[H+]
pH = 2.26
2) at the 1st equivalence point.
The solution is now completely composed of a salt of a weak acid. The pH of this solution will be basic.
1) Calculate molarity of KOH
molarity of KOH = 0.12 M
number of moles of acid will equal to base at equivalent point
2.0 x 10-3 mol / L = 0.12 M
L = 16.66 ml
Calculate the Kb of sodium acetate:
Kw = KaKb
1.00 x 10-14 = (1.48 x 10-4 ) (x)
x = 6.75 x 10-11
Calculate pH of the solution:
6.75 x 10-11 = [(x) (x)] /[0.12 M]
x = 2.84 x 10-6 M (this is the hydroxide ion concentration)
pOH = 5.54
pH = 8.45
similarly all ..
c) Calculate moles of acid and base in solution before reaction:
CH3COOH: 2.0x 10-3 mol
KOH: (0.005 L) (0.120 mol/L) = 6.0 x 10-4 mol
Determine amounts of acid and acetate ion after reaction:
CH3COOH: 2.0x 10-3 mol - 6.0 x 10-4 mol = 1.4 x 10-3 mol
CH3COONa: 6.0 x 10-4 mol
Use Henderson-Hasselbalch equation to determine pH of (now) buffered solution:
pH = 3.83+ log (6.0 x 10-4 / 1.4 x 10-3)
pH = 3.462
similarly do all...
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.