Introduction to redox reactions References Tindale, Ritchie et al, 2014, Chemistry for CSEC 2nd Edition, Nelson Thornes. p156-159 Electron Transfer in Redox Reactions Todayhttps://www.sewanhakaschools.org

1. Oxidation-Reduction Reactions
(Redox Reactions)

2. 2
The chemical changes that occur when electrons
are transferred between reactants are called
oxidation – reduction reactions

3. 3
Oxidation
- originally meant combining with oxygen
- iron rusting (iron + oxygen)
Reduction
- originally meant the loss of oxygen from a
compound
removing iron from iron ore ( iron II oxide)

4. 4
Redox reactions as an Electron Transfer
OXIDATION means: a LOSS of ELECTRONS
REDUCTION means: a GAIN of ELECTRONS
Oxidation reactions are always accompanied by a reduction reaction
These reaction are called redox reactions
You can use these Memory Devices to help :
 OIL RIG (Oxidation Is Loss, Reduction Is Gain)
 LEO the lion says GER (Lose Electrons Oxidation, Gain Electrons Reduction)

5. How do we write redox half equations?
Oxidation is…
the loss of electrons(oxidation
half equation)
Na(s) Na+(g)+ e-
notice the electrons are on the right
Reduction is…
the gain of electrons
(reduction half equation)
Cl2(g)+ 2e-  2Cl- (aq)
notice electrons are on the left

6. Examples of Redox reactions

7. Burning magnesium in oxygen
• Overall equation: 2Mg(s) +O₂ (g) 2MgO(s)
• The magnesium oxide (MgO) produced in the reaction is an ionic compound
consisting of Mg2+ and 2O2- ions
• During the reactions:
• Each magnesium atom loses two electrons to form a magnesium ion.
• Magnesium (Mg) is oxidized.
• Mg(s) Mg2+
(s) + 2e⁻
• Each oxygen atom in the oxygen molecule gains two electrons to form an
oxide ion.
• Oxygen (O₂) is reduced
• O2(g) + 4e⁻ 2O2-
(s)

8. Adding Zinc to Copper Sulphate Solution
• When a strip of zinc metal is placed into a blue solution of copper (II) sulphate a reaction
immediately begins as the zinc strip begins to darken. If left in the solution for a longer period of
time, the zinc will gradually decay due to oxidation to zinc ions. At the same time, the copper (II)
ions from the solution are reduced to copper metal which causes the blue copper (II) sulphate
solution to become colorless.
• The zinc displaces the copper in the copper (II) sulphate to form zinc sulphate and copper.
• Ionic equation for the reaction : Zn(s)+Cu2+ (aq)→Zn2+ (aq)+Cu(s)
• During the reaction:
Each zinc atom loses two electrons to form zinc ion. Zn is oxidized
• Zn(s)→Zn2+ (aq)+2e⁻
Each copper (II) ion gains two electrons to form a copper atom. The copper (II) ions (Cu2⁺) are
reduced
• Cu2+ (aq)+2e⁻ →Cu(s)

9. Bubbling Chlorine gas through Potassium
Bromide solution
• Overall reaction:Cl2(aq) + 2KBr(aq) → 2KCl(aq) + Br2(aq)
• The chlorine gas displaces the bromine in the potassium bromide to form potassium
chloride and bromine.
• The ionic equation for the reaction
• Cl2(aq) + 2Br⁻(aq) → 2Cl ⁻(aq) + Br2(aq)
• During the reaction
• Each bromide ion loses one electron to form bromine atom. The bromide ions are is
oxidized
• 2Br ⁻(aq) → Br2 (aq) + 2e ⁻
• Each chlorine in the chlorine molecule gains one electron to form a chloride ion. Chlorine is
reduced
• Cl2(g)+2e ⁻ →2Cl ⁻(aq)