Chemistry 12 Unit 5

I. Oxidation – Reduction Reactions:

Oxidation: A substance losing electrons.

Reduction: A substance gaining electrons.

eg: Al(s) in CuCl2(aq)

Al(s) + CuCl2(aq) Cu(s) + AlCl3(aq)(not balanced)

Net Ionic Equation:Al(s) + Cu2+

(aq) Cu(s) + Al3+(aq)

Reduction Half-Reaction:Cu2+

(aq) + 2e- Cu(s)

Oxidation Half-Reaction:Al(s) Al3+

(aq) + 3e-

• The reaction shows that Cu2+ wants electrons more than Al3+

• This type of reaction is called an “oxidation – reduction” reaction or a “redox” reaction.

• Aluminum metal is oxidized and copper (II) ions are reduced.

• The complete redox equation consists of some multiple of the two half-reactions:

Cu2+(aq) + 2e- Cu(s)

Al(s) Al3+(aq) + 3e-

3 ( )

2 ( )

• This shows the same number of electrons gained as lost:

2Al(s) + 3Cu2+(aq) + 6e-

2Al3+(aq) + 3Cu(s) + 6e-

Balanced Redox Equation:2Al(s) + 3Cu2+

(aq) 2Al3+(aq) + 3Cu(s)

• Always check that the total charge on each side of the equation is equal.

2Al(s) + 3Cu2+(aq) 2Al3+

(aq) + 3Cu(s)

3(2+) = 2(3+)

Terminology:

In this example:

Cu2+ is the oxidizing agent.

Al is the reducing agent.

Cu2+ is reduced to Cu.

Al is oxidized to Al3+.

For each of the following, which substance is oxidized and which substance is reduced?

1. Zn + CuSO4 ZnSO4 + Cu

Redox Practice I:

2. CrCl3 + Sn Cr + SnCl4

3. Fe + CuSO4 FeSO4 + Cu

4. MgCl2 + Cr Mg + CrCl3

5. Al + Pb(NO3)2 Al(NO3)3 + Pb

Substance Oxidized

Substance Reduced

For each of the following, which substance is the oxidizing agent and which is the reducing agent?

1. CuSO4 + Zn ZnSO4 + Cu

Redox Practice II:

2. Sn + CrCl3 Cr + SnCl4

3. Fe + CuSO4 FeSO4 + Cu

4. Mg + CrCl3 Cr + MgCl2

5. Al(NO3)3 + Pb Pb(NO3)2 + Al

Oxidizing Agent

Reducing Agent