Question

Calculate the initcial I^- concentration in a solution containing 3.0 mL of 0.20 M KI, 5.0 mL of 0.15 M (NH4)2S2O8, 5.0 mL of 0.25 M (NH4)SO4, 6.0 mL of 0.10 M KNO3, and 1.0 mL of 0.012 M Na2S2O3.

Answer 1

Initially I- will only come from KI

KI ----> K+ + I-
3.0 mL of 0.20 M KI
Nmber of moles of I- = M*V
                                             = 0.2 M * 3 mL
                                             = 0.6 mmol

Total volume of solution = 3 mL + 5 mL + 5 mL + 6 mL + 1 mL = 20 mL

concentration of I- = number of moles of I- / volume of solution
                                       = 0.6 mmol/ 20 mL
                                       = 0.03 M
Answer: 0.03 M