Question

Argentometre titrations, typically, are titrations using a standard solution of silver ions to form a silver halide precipitate. Calculate the pAg' value when 250 mL of 0.100 M AgNO, is added to 25.0 mL of 0.0500 M chloride ion. Iron in the +2 oxidation state reacts with potassium dichromate to produce Fe) and CH according to the equation: 6 Fe? + Cr,0,- + 14 H 6 Fe +2 Crl + 7 H,O How many milliliters of 0.1658 molar K Cr,O, are required to titrate 200.0 mL of 0.2500 molar Fesolution?

Answer 1

19)

No of mol of AgNO3 = M*V

           = 25*0.1 = 2.5 mmol

concentration of AgNO3 in the mixture = n/V = 2.5/50 = 0.05 M

No of mol of chloride ion(Cl-)     = 25*0.05 = 1.25 mmol

concentration of Cl- in the mixture = 1.25/50 = 0.025 M

1 mol Ag+ = 1 mol Cl-

concentration of Ag+ excess in the mixture = 0.05-0.025 = 0.025 M

pAg+ = -log[Ag+]

     = -log0.025

     = 1.6

20) from equation,

   6 mol Fe2+ = 1 mol Cr2O7-2(aq)

No of mol of Fe+2 taken = 200*0.25 = 50 mmol

No of mol of K2Cr2O7 required = 50/6 = 8.33 mmol

volume of K2Cr2O7 required = 8.33/0.1658 = 50.2 ml