Redox Reactions

Question 1

Oxidation and reduction definitions:

Answer 1

Oxidation: gain of oxygen, loss of hydrogen, loss of electrons, increase in o.n.
Reduction: loss of oxygen, gain in hydrogen, gain in electrons, decrease in o.n.

Question 2

Rules for assigning oxidation number:

Answer 2

1. o.n. of an atom in elemental state is 0
2. o.n. of hydrogen is +1, but is -1 in metal hydrides
3. o.n. of fluorine is -1
4. o.n. of oxygen is -2 in all compounds but is -1 in peroxides, -0.5 in superoxides,, and +2 in OF2.
5. In monoatomic ions, o.n. is the charge of the ion
6. In polyatomic ions, sum of o.n. is charge of the ion.
7. In a compound, sum of o.n. is 0.

Question 3

Balancing redox equation in acidic medium:

Answer 3

1. Construct unbalanced half equations
2. Balance the element oxidised/reduced
3. Balance O atoms by adding H2O
4. Balance H atoms by adding H+ ions
5. Balance overall charges by adding e-
6. Make e- gained = e- lost
7. Put half equations together and eliminate common terms

Question 4

Balancing redox equation in basic medium:

Answer 4

1. Construct unbalanced half equations
2. Balance the element oxidised/reduced
3. Balance O atoms by adding H2O
4. Balance H atoms by adding H+ ions
5. Balance overall charges by adding e-
6. Neutralise H+ ions by adding OH- on both sides
7. Combine OH- and H+ ions to make H2O
8. Eliminate common terms and balance half equations
9. Make e- gained = e- lost
10. Put half equations together and eliminate common terms