Question

Consider titration of 10.00 mL of 0.120 M Cu2+ solution with 0.100 M EDTA at pH 10.0. Find the concentration of free Cu2+ at the equivalence point of this titration.

Answer 1

Volume of Cu²⁺ (V1) = 10.00 mL

Concentration of Cu²⁺ (M1) = 0.120 M

Concentration of EDTA (M2) = 0.100 M

Volume of EDTA(V2) = V1 * M1 / M2 = (10.00 * 0.120) / 0.100 = 12.00 mL

Total Volume (V) = V1 + V2 = 10.00 + 12.00 = 22.00 mL

α_Y4 at pH 10.0 = 0.36

Formation constant for Cu²⁺ (K_f ) = 6.31*10¹⁸

Conditional formation constant, K_f' = α_Y4 * K_f = (0.36) * ( 6.31*10¹⁸) = 2.27*10¹⁸

Concentration of EDTA at equilence point, [EDTA] = (M2 * V2) / V = (0.100 * 12.00) / 22.00 = 0.05 M

Concentration of Cu^Y2-, [Cu^Y2-] = (M1 * V1) / V = (0.120 * 10.00) / 22.00 = 0.05 M

Concentration of free Cu²⁺ at the equivalence point, [Cu²⁺] =[Cu^Y2-] / (K_f' * [EDTA])

= 0.05 / (2.27*10¹⁸ * 0.05) = 4.41*10^-19

Concentration of free Cu²⁺ at the equivalence point = 4.41*10^-19