112. Solving a chemistry problem

19th century To separate copper(II) from iron(III) with subsequent titrimetric determination of copper(II), a strongly acid KU-2 cation exchanger in the H-form was used.
Sulphosalicylic acid and ammonia were added to the analyzed solution (H3L) containing copper(II) and iron(III) cations. In this case, the copper(II) cation passed into the cationic complex [Cu(NH3)4]2 sorbed by the cation exchanger, and the iron(III) cation into the anionic complex [FeCl3]6- , not sorbed by the cation exchanger. The resulting solution was passed through a chromatographic column with an H-form cation exchanger and, to completely remove the iron complex, the column was washed with a mixture of solutions of sulfosalicylic acid and ammonia, and then with water, after which the copper complex with the cation exchanger was eluted with a solution of hydrochloric acid, the column was washed with water and collected in a volumetric flask with a capacity of Vk(Cu), the elluate containing the Cu2 cation was diluted with water up to the mark.
Determination of copper(II) in the resulting solution was carried out by indirect iodometric titration. At the same time, V(Na2S2O3) of sodium thiosulfate with a molar concentration of the equivalent c(Na2S2O3) was used to titrate an aliquot of the solution with a volume of Va(Cu) ml.
Write the equations for the reactions that occur on the cation exchanger (R-H) when a solution containing copper(II) and iron(III) complexes is passed through it and when the copper complex is eluted from the cation exchanger. Using the data below, calculate the mass of copper in the analyzed solution. (II)
Option in
Vk(Cu), ml 100
Va(Cu), ml 25.00
c(Na2S2O3), mol/l 0.03525
V(Na2S2O3), ml 7.35