Question

A little stuck, could you please show working out?

Which of the following processes represents an oxidation reaction?

		1. ?Mg(s) -> Mg2+(aq)
		2. ?2H+(aq) -> H2(g)
		3. ?Cu2+(aq) -> Cu(s)
		4. ?I2(s) -> 2I-(aq)

Which one of the following processes represents a reduction reaction?

		1. ?Zn(s) -> Zn2+(aq)
		2. ? ?2Cl-(aq) -> Cl2(g)
		3. ? ?H2(g) -> 2H+(aq)
		4. Cu2+(aq) -> Cu(s)

Answer 1

Remember, in an oxidation process the oxidation no increases and in a reduction process it decreases.

Example:    1. A to A⁺ , oxidation process as oxidation no. increases from 0 to 1.

                 2. B²⁺ to B³⁺ , oxidation process as oxidation no. increases from +2 to +3.

                   3. A^- to A , oxidation process as oxidation no increases from -1 to 0

                              ....etc

                                                                           and

                   1. A to A^2- , reduction process as oxidation no. decreases from 0 to -2.

                   2. C³⁺ to C , reduction process as oxidation no. decreases from +3 to 0.

                   3. B^-2 to B^-3 , reduction process as oxidation no. decreases from -2 to -3

                              .... etc.

Thus,

1. Mg to Mg²⁺ : oxidation process, as oxidation no. increases from 0 to +2.

2. 2H⁺ to H₂ : reduction process as oxidation no. decreases from +1 to 0.

3. Cu⁺² to Cu : reduction process as oxidation no. decreases from +2 to 0.

4. I₂ to 2I^- : reduction process as oxidation no. decreases from 0 to -1.

and

1. Zn to Zn⁺² : oxidation process, as oxidation no. increases from 0 to +2.

2. 2Cl^- to Cl₂ : oxidation process, as oxidation no. increases from -1 to 0.

3. H₂ to 2H⁺ : oxidation process, as oxidation no. increases from 0 to +1.

4. Cu⁺² to Cu : reduction process as oxidation no. decreases from +2 to 0.