Describe the oxidizing action of potassium dichromate and write the ionic equations for its reaction with:

(i) iodide (ii) iron(II) solution and (iii) H₂S

K₂Cr₂O₇ acts as a very strong oxidizing agent in acidic medium.

K₂Cr₂O₇ gets reduced and acts as an oxidizing agent by oxidizing Iodide to iodine

(i) K₂Cr₂O₇ oxidizes iodide to iodine

Cr₂O₇^2-+ 14H⁺+ 6e^-→ 2Cr³⁺ + 7H₂O

2I^-→ I₂ + 2e^- } x3

Overall: Cr₂O₇^2-+ 14H⁺+ 6I^-→ 2Cr³⁺ + 7H₂O+ 3I₂

(ii) K₂Cr₂O₇ oxidizes iron(II) to iron(III)

Cr₂O₇^2-+ 14H⁺+ 6e^-→ 2Cr³⁺ + 7H₂O

Fe²⁺→ Fe³⁺ + e^- } x6

Overall: Cr₂O₇^2-+ 14H⁺+ 6Fe²⁺→ 2Cr³⁺ + 7H₂O + 6Fe³⁺

(iii) K₂Cr₂O₇ oxidized H₂S to sulphur

Cr₂O₇^2-+ 14H⁺+ 6e^-→ 2Cr³⁺ + 7H₂O

H₂S → S + 2H⁺ + 2e^-} x3

Overall: Cr₂O₇^2-+ 8H⁺+ 3H₂S → 2Cr³⁺ + 7H₂O +3S