Question

Balance (oxidation no. method)
Q) Cu + HNO3 -> Cu(NO3)2 + N2O + H2O

​

Answer 1

Explanation:

Writing the oxidation numbers of all the atoms.

Cu

0

+

H

+1

N

+5

O

3

−2

→

Cu

+2

(

N

+5

O

3

−2

)

2

+

N

+4

O

2

−2

+

H

2

+1

O

−2

Change in Ox. no. has occurred in copper and nitrogen.

Cu

0

→

Cu

+2

(NO

3

)

2

H

N

+5

O

3

→

N

+4

O

2

Increase in Ox. no. of copper =2 units per molecule Cu.

Decrease in Ox. no. of nitrogen=1 unit per molecule HNO

3

.

To make increase and decrease equal, eq. (ii) is multiplied by 2

Cu+2HNO

3

→Cu(NO

3

)

2

+2NO

2

+H

2

O

Balancing nitrate ions, hydrogen and oxygen, the following equation is obtained:

Cu+4HNO

3

→Cu(NO

3

)

2

+2NO

2

+2H

2

O

This is the balanced equation.