Question

K2Cr2O7 acts as oxidizing agent in acidic medium. To maintain acidic medium dil H2SO4 used but not HCl(or) HNO3. Give reason.

Answer 1

Answer:

Potassium dichromate is powerful oxidizing agent in acidic medium. In presence of dilute sulphuric acid, it liberates nascent oxygen.

K

2

Cr

2

O

7

+4H

2

SO

4

→K

2

SO

4

+Cr

2

(SO

4

)

3

+4H

2

O+

Nascent oxygen

3(O)

In acidic medium, dichromate ion takes up electrons and acts as oxidizing agent.

Cr

2

O

7

2−

+14H

+

+6e

−

→2Cr

3+

+7H

2

O

The net ionic equations for its reaction with (i) iodide (ii) iron(II) solution and (iii) H

2

S are as shown below.

Cr

2

O

7

2−

+6I

−

+14H

+

→2Cr

3+

+3I

2

+7H

2

O

Cr

2

O

7

2−

+6Fe

2+

+14H

+

→2Cr

3+

6Fe

3+

+7H

2

O

Cr

2

O

7

2−

+3H

2

S+8H

+

→2Cr

3+

+3S+7H

2

O