(D) OXIDISING AND REDUCING AGENTS HC CHEMISTRY HC CHEMISTRY CHEMISTRY IN SOCIETY (D) OXIDISING AND REDUCING AGENTS

(D) OXIDISING AND REDUCING AGENTS Uses of oxidising agents HC CHEMISTRY HC CHEMISTRY (D) OXIDISING AND REDUCING AGENTS Uses of oxidising agents

(D) CHEMISTRY IN SOCIETY Uses of oxidising agents HC CHEMISTRY HC CHEMISTRY (D) CHEMISTRY IN SOCIETY Uses of oxidising agents After completing this lesson you should be able to : Oxidising agents are widely employed because of the effectiveness with which they can kill fungi and bacteria, and can inactivate viruses. The oxidation process is also an effective means of breaking down coloured compounds making oxidising agents ideal for use as ‘bleach’ for clothes and hair

Everyday uses for strong oxidising agents COPY Everyday uses for strong oxidising agents Oxidising agents are widely employed because of the effectiveness with which they can kill fungi and bacteria, and can inactivate viruses. The oxidation process is also an effective means of breaking down coloured compounds making oxidising agents ideal for use as “bleach” for clothes and hair. 4

Oxidising agents as bleach COPY Oxidising agents as bleach Oxidising agents are widely used in everyday life because of the effectiveness with which they can kill fungi, and bacteria and can inactivate viruses. The oxidising agents include bleaches and chemicals such as potassium permanganate, KMnO4.   5

Potassium permaganate (KMnO4) COPY Potassium permanganate solution will react with any organic matter in a pond including algae, bacteria, fish, particulate and dissolved organic, and organic bottom sediments. It has been used in fish ponds to treat common fish pathogens such as gill parasites and external bacterial and fungal infections. Athlete's foot, another fungal infection in humans can be treated with very dilute potassium permanganate solution. Chemistry world podcast – Potassium permaganate 6

Hydrogen peroxide

Hydrogen peroxide COPY The oxidation process is also an effective means of breaking down coloured compounds making oxidising agents ideal for use as "bleach" for clothes and hair. Hydrogen peroxide, H2O2(aq) can be used to bleach hair and it behaves here as an oxidising agent. In the reaction, coloured pigments in the hair, related to the pigment melanin are oxidised to colourless substances. H2O2(aq) + 2H+(aq) + 2e- → 2H2O(l)     8

How does Chlorine in swimming pools work? COPY Cl2+H2O→ HOCl + HCl Chlorine kills bacteria through a fairly simple chemical reaction. The chlorine solution you pour into the water breaks down into many different chemicals, including hypochlorous acid (HOCl) The hypochlorus acid is a strong oxidising agent and kills microorganisms by removing electrons from the bacteria destroying the cell walls and enzymes and structures inside the cell, rendering them harmless. 9

2HClO-(aq) + 2H+(aq) + 2e– → Cl2(g) + 2H2O(l) COPY Sodium hypochlorite Cl2 (g) + 2NaOH (aq) → NaClO (aq) + NaCl (aq) + H2O (l) Sodium hypochlorite has a wide application as a bleaching agent for textiles and textile laundering. It also acts as a powerful disinfectant. In solution the hypochlorite ions form hypochlorous acid, HClO. This is the oxidising agent. 2HClO-(aq) + 2H+(aq) + 2e– → Cl2(g) + 2H2O(l)   Household bleach is, in general, a solution containing 4-6% sodium hypochlorite Chemistry world podcast – sodium hypochlorite 10

Experiment 4 drops of yellow food colouring (E102) or 4 drops of blue food colouring (E 124) are dissolved in 40 cm3 of water. A solution containing 4 drops of household bleach in 20 cm3 of water is added to the solution and the mixture stirred. The hypochlorite oxidises the colourings taking the solution through a number of colour changes. 12

Luminol Chemilumenescence COPY Luminol can be oxidised by a solution of bleach to an aminophthalate ion which is produced in an excited state and emits light as it drops back into a ground state. 13

A bleach which is a reducing agent COPY A bleach which is a reducing agent Aran sweaters used to be bleached using sulphur dioxide gas on the wet sweaters. The reaction involves the dissolving of the gas to make a solution containing hydrogen sulphite. This produces some sulphite ions. SO2(g) + H2O(l) → H2SO3 (aq) 14

COPY SO32-(aq) + H2O(l) → SO42-(aq) + 2H+ + 2e- Oxidation     This is not an example of a bleach which is an oxidising agent. As the reaction is oxidation, SO2(g) in water and SO32-(aq) are examples of a bleach which is a reducing agent. They are described as anti-oxidants and are used to sterilise glass bottles in wine-making and are present in some foods. If you see E220 amongst the products of a food stuff, this represents sulphur dioxide. 15

2NaNO3(s) → 2NaNO2(s) + O2(g) Fire Writing In this particular case, sodium nitrate decomposes to give sodium nitrite (sodium nitrate(III)) and oxygen, and it is the oxygen released which helps to promote the burning process and produce the glow and charring: 2NaNO3(s) → 2NaNO2(s) + O2(g) Most other nitrates will also produce a similar effect, but potassium nitrate is less effective because it is less soluble and some other nitrates may give off very toxic nitrogen dioxide when they decompose.

Experiment Add a flower petal to a test tube SO2 What did you observe? 20

The following reactions take place when nitric acid is added to zinc. COPY The following reactions take place when nitric acid is added to zinc. NO3–(aq) + 4H+(aq) + 3e– → NO(g) + 2H2O(l) Zn(s) → Zn2+(aq) + 2e– How many moles of NO3– (aq) are reduced by one mole of zinc? A 2/3 B 1 C 3/2 D 2 A 21

COPY In which reaction is hydrogen gas acting as an oxidising agent? A H2 + CuO → H2O + Cu B H2 + C2H4 → C2H6 C H2 + Cl2 → 2HCl D H2 + 2Na → 2NaH D 22

COPY Iodide ions can be oxidised using acidified potassium permanganate solution. The equations are: 2I–(aq) → I2(aq) + 2e– MnO4–(aq) + 8H+(aq) + 5e– → Mn2+(aq) + 4H2O(l) How many moles of iodide ions are oxidised by one mole of permanganate ions? A 1.0 B 2.0 C 2.5 D 5.0 D 23