Answer:
Cu + 2NO3- + 4H+ ---------> Cu2+ + 2NO2 + 2H20
Step-by-step 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