Question

Cu(s) + 4HNO3 --> Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)

Cu2+(aq) + 4NH3(aq) --> [Cu(NH3)4]2+(aq)

a. For each reaction, identify the oxidation number for each of the elements on both sides of the equation.

b. Which of the reactions above is a redox reaction? Explain.

c. Identify the element that is being reduced and the one that is being oxidized in the redox reaction.

d. Identify the strong oxidizing agent and strong reducing agent in the redox reaction.

Answer 1

The oxidation states are as follows

Cu --> 0

HNO3 --> H(+1) , N(+5) , O(-2)

Cu(NO3)2 ---> Cu (+2) , N(+5) , O(-2)

NO2 ---> N (+4) , O(-2)

H2O ---> H(+1) , O(-2)

0            +5            +2                     +4

Cu(s) + 4HNO3 -----> Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)

Oxidation half reaction :Cu(s) -----> Cu(NO3)2(aq)

Reduction half reaction : HNO3 -----> NO2(g)

Here the oxidation state of Cu increases from 0(in Cu) to +2(in Cu(NO3)2) so Cu is oxidized and the oxidation state of N decreases from +5(in HNO3) to +4(in NO2) so N is reduced

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+2            -3 +1            +2 -3 +1

Cu2+(aq) + 4NH3(aq) --> [Cu(NH3)4]2+(aq)

Here the oxidation state of the elements neither changes so it not a redox reaction.