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in Chemistry by (49.6k points)

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

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

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Potassium dichromate, in acidic medium acts as a strong oxidising agent by gaining 6e’ and forms Cr3+.
Cr2O72- + 14H+ + 6e → 2Cr3+ + 7H2O   ..(1)

(i) iodides
6I → 3I2 + 6e ..(2)
(1) + (2)
Cr2O72- + 14 H+ + 6I → 2Cr3+ + 3I2 + 7H2O

(ii) iron (II) solution
6Fe2+ → 6Fe3+ + 6e ..(3)
(1) + (3)
Cr2O72- +14H++ 6Fe2+ → 2Cr3+ + 6Fe3+ + 7H2O

(iii) H2S
3H2S → 6H+ + 3S + 6e ..(4)
(1) + (4)
Cr2O72- +14H+ + 3H2S → 6H+ + 3S + 2Cr3+ + 7H2O

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