1. (D) OXIDISING AND REDUCING AGENTSHC
CHEMISTRY HC
CHEMISTRY
CHEMISTRY IN SOCIETY
(D) OXIDISING AND REDUCING AGENTS

2. Molecules and group ions can act as oxidising agentsHC
CHEMISTRY HC
CHEMISTRY
(D) OXIDISING AND REDUCING AGENTS
Molecules and group ions can act as oxidising agents

3. HC HC (D) CHEMISTRY IN SOCIETY
Molecules and group ions can act as oxidising agents
After completing this lesson you should be able to :
The dichromate and permanganate ions are strong oxidising agents in acidic solutions. Hydrogen peroxide is an example of a molecule which is an oxidising agent.
Carbon monoxide is an example of a gas that can be used as a reducing agent.

4. Remember COPY Something is oxidised if It gains oxygen
It loses electrons (O.I.L.)
Its oxidation state increases (advanced higher)
Something is reduced if
It loses oxygen
It gains electrons (R.I.G.)
Its oxidation state decreases (advanced higher)

5. Molecules and group ions can act as oxidising and reducing agents
COPY
Molecules and group ions can act as oxidising and reducing agents
Compounds can also act as oxidising or reducing agents.
The electrochemical series contain a number of ions and molecules.
Oxidising and reducing agents can be selected using an electrochemical series. 5

6. Fe(l) COPY EXTRACTING IRON – THE BLAST FURNACE C(s) + O2(g) CO2(g)
Iron ore, coke (carbon) and limestone enter the furnace from the top of the furnace.
Iron is extracted from its ore using carbon. The reaction requires a lot of heat. To provide the necessary heat the reaction is carried out in a BLAST FURNACE.
The extraction of the iron happens in 3 stages.
STAGE 1: The coke (carbon) burns to produce carbon dioxide CO2.
Molten iron flows to the bottom of the furnace.
C(s) + O2(g) CO2(g)
STAGE 3
STAGE 2: The CO2 from stage 1 reacts with more carbon to form carbon monoxide CO.
STAGE 2
CO2(g) + C(s) CO(g)
STAGE 1
STAGE 3: The CO from stage 2 reacts with iron(III) oxide Fe2O3 in the iron ore removing the oxygen.
HOT AIR BLAST
HOT AIR BLAST
Fe(l)
Fe2O3(s) + 3CO(s) Fe(l) + 3CO2(g)

7. COPY
heat
iron(III) oxide
carbon monoxide +
iron +
carbon dioxide
heat
Fe2O3 + 3 CO 2 Fe 3
CO2 + N5
CHEMISTRY
Ionic equation:
heat
(Fe3+)2(O2-)3 + 3 CO 2 Fe + 3
CO2
The iron(III) ion is changed to an iron atom. To do this each iron(III) ion has to gain 3 electrons. This change is reduction.
Fe3+ +
3 e- Fe

8. N5 OXIDATION AND REDUCTION AGAIN!! COPY
CHEMISTRY
COPY
OXIDATION AND REDUCTION AGAIN!!
The terms OXIDATION and REDUCTION originates from the extraction of metals industry. These terms were used for centuries before atoms and electrons were discovered.
An OXIDATION reaction is a reaction where a reactant GAINS OXYGEN ATOMS.
An REDUCTION reaction is a reaction where a reactant LOSES OXYGEN ATOMS.
The extraction of iron from iron(III) oxide in the BLAST FURNACE shows these original definitions of OXIDATION and REDUCTION.
heat
iron(III) oxide
carbon monoxide +
iron +
carbon dioxide
heat
Fe2O3 + 3 CO 2 Fe + 3
CO2
The iron(III) oxide has LOST OXYGEN ATOMS to produce iron. It has been REDUCED.
The carbon monoxide has GAINED an OXYGEN ATOM to produce carbon dioxide . It has been OXIDISED.

9. 1. Permaganate MnO4- is a strong oxidising agent
COPY
Oxidising agents such as potassium permaganate (KMnO4) are
used in explosives and fire works
MnO4-(aq) + 8H+ +5e- → Mn2+(aq) + 4H2O(l)
Mn(VII) Mn(II) 9

10. When pure glycerol is poured onto a pile of potassium permanganate, white smoke is produced in the beginning. Oxidation of glycerol with potassium permanganate is an exothermic process, heat released in the reaction being enough to cause glycerol to evaporates. As the reaction proceeds, more and more heat is released in the reaction and glycerol is eventually ignited. Because of presence of potassium ions (from potassium permanganate), the flame is violet in colour. Although there are lot of reaction pathways and lot of products formed during the combustion, the following equation shows the main process in which glycerol is completely oxidized to carbon(IV) oxide.
The black residue after the reaction is mostly a mixture of manganese(III) oxide and/or manganese(IV) oxide and potassium carbonate.

11. Redox chemistry  At advanced level, the redox nature of the reaction can be explored. Do this by allowing the residue to cool down and then dissolving it in water. This produces a green solution suggesting the presence of a Mn(Vl) species, as well as a brown solid, manganese(lV) oxide. This confirms the reduction of the manganate(Vll) ion; the glycerol has been oxidised to water (hence the steam) and carbon dioxide.
The most stable is +2, which is a pale pink color in aqueous solutions. Also important is +4, brown/black, which is found in manganese dioxide; and +7 found in the purple permanganate anion MnO4–. Manganese's +6 oxidation state is green.

12. MnO4-(aq) + 8H+ + 5e- → Mn2+(aq) + 4H2O(l)
2. Dichromate and permanganate in acidic solutions are strong oxidising agents.
Cr2O72-(aq) + 14H+(aq) + 6e- → 2Cr3+(aq) + 7H2O(l)
Orange green
Oxidation of alcohols –revisited
REDOX GUIDE
MnO4-(aq) + 8H+ + 5e- → Mn2+(aq) + 4H2O(l)
Purple colourless
Both half equations contain H+ ions showing they are strong oxidising agents in the presence of acid
COPY 12

13. Demonstration
The action of CuO as an oxidising agent for alcohols can be shown by placing a small amount of ethanol in an evaporating basin. A 2p coin is then heated to just below red heat in a Bunsen and then wafted in the air allowing the surface to become coated in black copper(II) oxide. The warm coin is then carefully lowered into the ethanol. Instantly the bright shiny surface of the coin is restored as the CuO is reduced to copper. The process of heating the coin — forming the oxide — and reducing the oxide in alcohol is repeated until little liquid is left in the dish. At this point, if pH indicator is added, it shows that an acid has formed whilst the distinctive smell of ethanal can be detected.

14. Unit 2 re-visited

15. 3. An Oxidation and Reduction reaction – Blue Bottle experiment
COPY
Glucose (an aldohexose) in an alkaline solution is slowly oxidised by oxygen, forming gluconic acid: 
CH2OH-(CHOH)4-CHO + ½O2   CH2OH-(CHOH)4-CO2H  
In the presence of sodium hydroxide, gluconic acid is converted to sodium gluconate. Methylene blue speeds up the reaction by acting as an oxygen transfer agent. As glucose is oxidised by the dissolved oxygen, methylene blue itself is reduced, forming the colourless methylene white, and the blue colour of the solution disappears. 15

16. The stopper must be taken off to allow more oxygen in.
What to do
1. Put some water in the conical flask. Put in the stopper. Shake vigorously to check for leaks. If there are none, pour the water away and proceed.
2. Put 100 cm3 of potassium hydroxide solution into a conical flask.
3. Add 3.3 g dextrose.
4. Add 3–4 drops of methylene blue indicator.
5. Put a stopper on the flask.
6. Shake vigorously.
7. When the solution clears, repeat the process.
8. It is necessary periodically to remove the stopper.
Methylene blue is reduced by the alkaline dextrose solution to produce a colourless solution.
When the solution is shaken, it is oxidised by the oxygen in the flask to produce the blue dye.
The stopper must be taken off to allow more oxygen in. 16

17. 4. Potassium chlorate is a strong oxidising agent
COPY
Potassium chlorate is a very strong oxidizing agent that oxidizes the sugar in the jelly baby almost instantaneously.  When the experiment is performed, the jelly baby bursts into giant flames and a screaming sound can be heard as rapidly expanding gases are emitted from the test tube in which the experiment is performed. The smell of candy floss is also given off. 
2KClO3  2KCl(s) + 3 O2 C12H22O11(s) + 12O2(g)  12CO2(g) + 11H2O(g)

18. 5. Hydrogen peroxide is a strong oxidising agent
COPY
Oxidising agents such as hydrogen peroxide are used in many
bleaching products
H2O2(aq) + 2H+(aq) + 2e- → 2H2O(l) 18

19. Elephant Toothpaste Chemistry
COPY
The overall equation for this reaction
is:
2 H2O2(aq)  2 H2O(l) + O2(g)
The catalyst is potassium iodide. Some of the iodide ions are
converted to I2 molecules by the hydrogen peroxide
H2O2(aq) + 2H+(aq) + 2e- → 2H2O(l)
2I-(aq) → I2(s) + 2e-
H2O2(aq) + 2H+(aq) + 2I-(aq) → I2(s) + 2H2O(l) 19