Oxidation-Reduction Reaction:

an oxidation-reduction or redox reaction refers to a reaction where electrons are transferred between reactants;

Oxidation refers to the loss of electrons.

Reduction refers to the gaining of electrons.

An Oxidizing Agent is an element which causes oxidation (and is reduced as a result) by removing electrons from another species.

A Reducing Agent is an element which causes reduction (and is oxidized as a result) by giving electrons to another species.

Oxidation Number:

Monoatomic ions: actual charge of the atom that results from the loss or gain of electrons

Atoms (not in ionic form):

o charge tthat the atom would develop if combined with other atoms by electron transfer

o hypothetical charge assigned to the atom using a set of rules

Examples:

Element Compound/Ion Oxidation State

Mg Mg(NO3)2 +2

I I2 0

S Na2S2O3 +2

S Na2S4O6 +5, +5, 0, 0

Objectives:

1. To recognize the visible indications of a redox reaction2. To assign oxidation states to different elements in a compound3. To identify the reducing and oxidizing agents of a reaction4. To balance redox reactions using a change-in-oxidation-state

methodActivity Series:

METHODOLOGY

Four test tubes were labelled A, B, C, and D

The ff. were mixed in test tube D:

2 drops 0.1M KMnO4

6 drops 6M H2SO4

6 drops 0.1M Na2C2O4

The ff. were mixed in test tube C:

2 drops 0.1M I2 in KI

2 drops 0.1M Na2S2O3

The ff. were mixed in test tube B:

2 drops 0.1M K2Cr2O7

6 drops 6M H2SO4

4 drops 3% fresh H2O2

The ff. were mixed in test tube A:

5 drops 0.1M Cu(NO3 )2

Mg ribbon

Each test tube was observed for evolution of gas and other visible reactions.

RESULTS

Test Tube Balanced Equation Observations

A Cu(NO3)2+ Mg Mg(NO3 )2 + Cu

Liquid: blue to yellow (colorless)

Solid: Silvery white ribbon to black(reddish brown) specks

B K2Cr2O7 + 4 H2SO4 + 3 H2O2 K2SO4 + Cr2(SO4)3 + 3 O2 + 7 H2O

Effervescence

C 2Na2S2O3 + I2 Na2S4O6 + 2 NaIYellow(reddish brown) to colorless

D2KMnO4 + 8 H2SO4 + 5 Na2C2O4

2 MnSO4 + 10 CO2 + 8 H2O + 5Na2SO4 + K2SO4

Purple to colorless

DISCUSSION

lost e-; oxidized; R.A.

+2 +5 -2 0 +2 +5 -2 0

Cu ( NO3 ) 2 + Mg Mg ( NO3 )2 + Cu

gained e-; reduced; O.A.

Mg is more reactive and more likely to be oxidized than Cu.

+1 +6 -2 +1+6 -2 +1 -1 lost e-

K2 Cr2 O7 + 4 H2SO4 + 3 H2O2 oxidized

R.A.

gained e- +1+6-2 +3 +6 -2 0 +1-2

reduced; O.A. K2SO4 + Cr2 (SO4)3 + 3 O2 + 7 H2O

lost e-; oxidized; R.A.

+1 +2 -2 0 +1+2.5-2 +1 -1

2 Na2S2O3 + I2 Na2S4O6 + 2 NaI

gained e-; reduced; O.A.

+1 +7 -2 +1+6-2 +1 +3 -2 lost e-; oxidized; R.A.

2 KMn O4 + 8 H2SO4 + 5 Na2C2O4

gained e-; reduced; O.A.

+2+6-2 +4 -2 +1 -2 +1+6-2 +1+6-2

2 MnSO4 + 10 CO2 + 8 H2O + 5 Na2SO4 + K2SO4

Sources:

http://ibchem.com/IB/ibnotes/brief/red-sl.htm