redox

Question

In which of the following willa redox reaction occur?
A. adding sodium to ethanol
B. bubbling SO2 into NaOH solution
C. heatin Cu(II)hydroxide
D. adding zinc oxide to concentrated nitric acid

Why the answer is A but NOT D?

Answer 1

A.
2Na + CH3CH2OH → 2CH3CH2O^-Na^+ + H2
Na is oxidized because its oxidation number (O.N.) increases from 0 (in Na) to +1 (in Na^+).
H is reduced because its O.N. decreases from +1 (in -OH) to 0 (in H2).

B.
SO2 + 2NaOH → Na2SO3 + H2O
SO2 + Na2SO3 + H2O → 2NaHSO3
The reactions are not redox because there is no change in O.N. for any element in the reactions.
O.N. : S = +4, O = -2, Na = +1, H = +1 (on both sides)

C.
Cu(OH)2 → CuO + H2O
The reaction is not redox because there is no change in O.N. for any element in the reaction.
O.N. : Cu = +2, O = -2, H = +1 (on both sides)


D.
ZnO + 2HNO3 → Zn(NO3)2 + H2O
The reaction is not redox because there is no change in O.N. for any element in the reaction.
O.N. Zn = +2, O = -2, H = +1, N = +5 (on both sides)

Answer 2

A. adding sodium to ethanol

2Na + CH3CH2OH --> 2CH3CH2ONa + H2

Na is oxidized and hydrogen reduced.

D. adding zinc oxide to concentrated nitric acid

ZnO + 2HNO3 --> Zn(NO3)2 + H2O

This is a neutralization and no oxidation number for any element involved in the reaction.