Use oxidation numbers to identify which of these reactions are REDOX reactions: a) 2SO2 + O2 -> 2SO2 b) 3NO2 + H2O -> 2HNO3 + NO c) SO2 + H2O -> H2SO3

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ncchemist | eNotes Employee

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You can only ask one question at a time so I edited out your second question.

A:  You have a mistake in your reaction.  I suspect you mean:

2SO2 + O2 --> 2SO3

The SO2 has the S in the +4 oxidation state and O in the -2.  The SO3 has the S in the +6 state and the O in the -2.  So the sulfur goes from +4 to +6.  In other words, it loses two electrons and becomes oxidized.  So this is a redox reaction (the oxygen is reduced).

B:  The NO2 has the N in the +4 state and the O in the -2 state.  The HNO3 has the N in the +5 state and the O in the -2 state (this gives the NO3- anion a total charge of -1).  The NO has the N in the +2 state and the O in the -2 state.  So two of the NO2 molecules are oxidized to HNO3 and one is reduced to NO.  This is a redox reaction.

C:  The SO2 has the S in the +4 state and the O in the -2 state.  The H2SO3 has the S also in the +4 state since the SO3 anion must have a -2 charge.  So nothing is oxidized, therefore it is not a redox reaction.

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