55. Solving a chemistry problem

8. 0.05 n. a solution of 1,4-naphthoquinone was titrated with a 0.033 N solution of FeCl2, both solutions were 1 N in HCl and contained 50 vol.% ethanol. EMF was measured between a platinum electrode in a titratable solution and a calomel electrode in the same solution. The potential of the calomel electrode in this solution is 0.2531 V relative to the standard hydrogen electrode (in the same solvent).
After adding to 17.1 ml of a solution of 1,4-naphthoquinone A, ml of a solution of FeCl2, the EMF became equal to E B. Calculate the standard redox potential (B) of 1,4-naphthoquinone (at pH = 1), assuming the activities of organic substances to be unity . The average activity coefficient of HCl in 1 N solution is 0.81.
A ml 3
E B, 0.2450