Question

What is the final, balanced equation that is formed by combining these two half reactions?

Answer 1

Answer:

Cu + 2NO3- + 4H+ ---------> Cu2+ + 2NO2 + 2H20

Explanation:

The half reactions are;Cu ----------> Cu2+ + 2e-

NO3 + 2e + 2H* —------> N02 + H20

It is worthy to note that oxidation is the an increase in oxidation number while reduction is a decrease in oxidation number.

In the first half reaction involving Copper, copper has been oxidized as its oxidation number increased from 0 to +2.

IN the reduction half reaction, NO3- has been reduced as its oxidation number decreased from +5 to +4.

In balancing half reactions, the following must be observed;

1. split the reactions into half equations, one for oxidation and the other for reduction.

Cu ------> Cu2+ + 2e-   ( oxidation)

NO3- + 2e- -----> NO2   (reduction).

2. balance on half with respect to atoms and charges.

3. balance the other half with respect to atoms and charges

4. balance by adding H+ ions in acidic solution

NO3- + e- -------> NO2

(-1 )       (-1)             (0)

NO3- + 2H+ +e- -------> NO2

(-1)       (+2)     (-1)            (0)

5. balance hydrogen by adding water molecules

NO3 - + 2H+ + e - -------->  NO2 + H2O

6. combine both equations

Cu ---> Cu2+ + 2e-                                  *1

NO3- + 2H+ + e- -------> NO2 + H2O      *2

= Cu -----> Cu2+ + 2e-

2NO3- +4H+ + 2e- -------> 2 NO2 + 2H20

Combined equation  = Cu + 2NO3- + 4H+ ---------> Cu2+ + 2NO2 + 2H20