Provide the following information for a titration analysis involving a titrant a

Question

Provide the following information for a titration analysis involving a titrant and titrand, where the titrand is a weak, diprotic acid (Kai = 1.00 x 104; Ka2 = 1.00 x 10^-8; Vol=0.01000 L; FH_2A=0 and the titrant is a strong monoprotic base that has been standardized (0.1000 M KOH). Calculate the pH at the following volumes of added strong base: A. 0.00 mL of strong base (KOH) added, B. at one-half the equivalence volume, C. at the first equivalence volume, D. at 3/2 the first equivalence volume, E. at the second equivalence volume (2'Ve1), and F. at 0.03000 L of added hydroxide. Sketch the titration curve, making sure to include ALL pertinent information.

Explanation / Answer

pKa1 = 4.0

pKa2 = 8.0

millimoles of H2A = 0.01 x 0.1 = 0.001

a) 0.00 mL

H2A ----------------------> H+   + HA-

0.1 0               0---------------------> initial

0.1-x                           x                x -----------------> equilibrium

Ka1 = x^2 /0.1-x

1.0 x 10^-4 =x^2 /0.1-x

x^2 + 1.0 x 10^-4 x - 1.0 x 10^-5 = 0

x = 0.00311

x = [H+] = 0.00311M

pH= -log[H+] = -log(0.00311)

pH = 2.51

b) at one-half equivalence point :

at this point pH = pKa1

pH = 4.0

c) at first equivalence point :

it is equivaelce point . at this main species HA-

so

pH = 1/2 [pKa1 + pKa2]

pH = 1/2 [4 + 8]

pH = 6.0

d) at 3/2 first equivalence volume :

this is also called as second half equivalence point

here pH = pKa2

pH = 8.0

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