Question

.A 2.00 mL solution of apotransferrin was titrated with soluble iron via the reaction below. It required 163 μL of 1.43 mM ferric nitriloacetate to reach the endpoint.

?????????????? + 2??3+ → (??3+)2???????????

The titration was monitored by measuring the absorbance of the dark red iron-transferrin product at a maximum absorption wavelength of 465 nm. a. At the equivalence point, the slope of the absorbance vs. volume of Fe3+ added graph changes abruptly. Why does this occur? b. What is the concentration, in mol/L, of the apotransferrin in the original solution?

Answer 1

a. At the equivalence point, the absorbance vs volume changes abruptly because

upto the equivalence point , the added volume of Fe3+ will react with apotransferrin and get converted to the iron-transferrin complex. After the equivalence point the excess Fe3+ will give a different absorption and hence the sbrupt change .

b. V1M1 = V2M2

Let M1 be the concentration of apotransferrin in mM.. V1 = volume of original solution = 2 mL = 2 x 10³ micro L

2 x 10³ M1 = 163 x 1.43

M1 = 116.545 mM = 0.1165 M = 0.1165 mol/L