Question

The molarity of the potassium permanganate can be determined by titrating it with a known amount of iron.

A. If a 0.1593 gram sample of iron metal is oxidized to form iron (II) in aqueous solution, the iron (II) requires 28.54 mL of KMnO₄(aq) solution to reach the endpoint. Determine the molarity of the KMnO₄(aq).

B. The titration of a 20.00 mL sample of potassium iodide required 22.4 mL of 0.1130 M sodium thiosulfate titrant. What is the molarity of potassium iodide solution?

Answer 1

a.

Following redox reaction takes place

Fe+ Mn 7+ --> Fe2+ +Mn2+

here we will make use of gram equivalents instead of moles

moles of Fe = 0.1593/ 56

= 0.02

N= 1.547

molarity= 1.547/ n factor

= 1.547/5

= 0.31 mol/l

b.

Na2S2O3 + 2KI = K2S2O3 + 2NaI

22.4 mL of 0.1130 M sodium thiosulfate= .0224 * .113 moles of sodium thiosulfate

=0.00253 moles of sodium thiosulfate

0.00253 moles of sodium thiosulfate= 2 * 0.00253 moles of KI

=0.00506 moles of KI

volume of KI = 20 ml

Conc = 0.00506/ (20*10^-3)

= 0.253 mol/l is the conc of KI