REDOXB2

Oxidation-Reduction Reactions ( continued)

Objective B: Given an oxidation-reaction, identify what is being oxidized and what is being reduced.

Example: CuCl2 + Fe = FeCl2 + Cu

For each atom, keep track of the oxidation number before and after the reaction:

Reactants: Oxidation number	Products: Oxidation number
In CuCl₂, each Cl = -1	In FeCl₂, each Cl = -1
In CuCl₂, Cu = +2, from x + 2(-1) = 0.	Cu = neutral = 0
Fe= neutral = 0	In FeCl₂, Fe = +2 from x + 2(-1) = 0.

Cu's oxidation number is reduced from 2 to 0. So Cu is reduced.

Fe's number increases from 0 to 2, so Fe is said to be oxidized.

If the oxidation number has decreased, the atom is said to have been reduced. The number decreases from a gain of electrons, which have a negative charge.

If the oxidation number has increased, the atom is said to have been oxidized. The number increases from a loss of electrons. Taking away negatives is adding to the positives.

What happens to atoms in redox reactions?

HONOLULU STAR BULLETIN

LEO the lion said GERrrrr!

L = Loss

E= of Electrons=

O = Oxidation

G= Gain

E= of Electrons

R= Reduction

Write half reactions for both Fe and Cu+2.

Remember Fe gets oxidized:

Fe --> Fe + 2e ( electrons are products, so they are being lost.

Cu⁺², meanwhile, gets reduced, so it gains electrons:

Cu⁺² + 2e --> Cu

In order for an atom to be reduced, it must gain electrons. But these electrons must first be given up by another atom.

So, oxidation and reduction always occur together.

More examples:

In each of the following, identify what is being oxidized and what is being reduced.

1. C + O2 ---> CO2

Answer:

carbon is oxidized from 0 to +4

each oxygen is reduced from 0 to -2

2. 2 Al + 3 Cu⁺² ---> 2 Al⁺³ + 3 Cu

Answer:

Each Al is oxidized from 0 to +3

each Cu⁺² is reduced from 2 to 0

3. 4 H⁺¹ + NO3^-1 + Fe⁺² ---> 2H₂O + NO + Fe⁺³

Answer:

N is reduced from +5 in the NO3^-1group to + 2 in NO.

Fe⁺² is oxidized from 2 to 3

Exercises for Objective B

1. In each of the following, identify what is being oxidized and what is being reduced.

a. Cu⁺² + Fe ---> Fe⁺² + Cu

b. Co + Sn⁺² ---> Co⁺² + Sn

c. 4H⁺¹ + NO₃^-1 + 3 Fe⁺² ---> 2 H₂O + NO + 3 Fe⁺³

d. 2 Cr + 3 Sn⁺² ---> 2 Cr⁺³ + 3 Sn

e. S^-2 + 2 NO₃^-1 + 4H⁺¹ ---> SO2 + NO2 + 2H2O

f. CH4 + 2 O2 ---> CO2 + 2H2O

g. 2 NH4⁺¹ + 2 NO3^-1 ---> 2 N2 + 4 H2O + O2

h. Al + SO4^-2 + H⁺¹ ---> SO2 + Al⁺³ + H2O

( not balanced, but don't worry )

i. Mg + CO2 ---> 2MgO + C

j. Cr2O7^-2 + SO3^-2 + H+1 --> Cr⁺³ + SO4^-2+ H2O

( not balanced, but don't worry )