liquid ethanol combustion in air. write the balanced chemical equation and identify the elements that are oxidized and reduced with the appropriate oxidation numbers. How do you do that?

Answer 1

Ethanol = C₂H₅OH (CH3CH2OH)

C₂H₅OH + 3O₂ ==> 2CO₂ + 3H₂O .. balanced equation for combustion of ethanol

Some general rules to know in order to find oxidation numbers:

Free elements have ox.no. of zero

H bonded to non-metals has ox.no. of +1. If bonded to metals or B, it is -1

O (oxygen) has ox.no. of -2 (except in H2O2 or if bonded to F)

Sum of all ox.no. must equal charge on ion or molecule

The oxidation state of O in O₂ is zero. The oxidation state of O is CO₂ and in H₂O is -2. So, O has been reduced.

The oxidation number of the alcohol carbon in C₂H₅OH is -1 and the other C is -3. The oxidation number of C is CO₂ is +4. So C has been oxidized.