What is Oxidation?

Oxidation is the process where a substance gains oxygen or loses electrons. Non-metals are good oxidizing agents because they tend to accept electrons from other substances, thereby oxidizing them.

How Non-Metals Act as Oxidizing Agents

Non-metals gain electrons to form negative ions. The number of electrons gained equals the valency of the non-metal:

• Chlorine (Cl): $\text{Cl} + e^- \rightarrow \text{Cl}^-$ (gains 1 electron, valency 1)
• Oxygen (O): $\text{O} + 2e^- \rightarrow \text{O}^{2-}$ (gains 2 electrons, valency 2)
• Nitrogen (N): $\text{N} + 3e^- \rightarrow \text{N}^{3-}$ (gains 3 electrons, valency 3)

Examples of Oxidizing Properties

Oxygen: Oxygen is a strong oxidizing agent. It oxidizes metals and non-metals:

$\text{C} + \text{O}_2 \rightarrow \text{CO}_2$

$\text{S} + \text{O}_2 \rightarrow \text{SO}_2$

In Tanzania, oxygen gas is used in hospitals for patients with breathing difficulties and in welding operations at construction sites.

Chlorine: Chlorine is a powerful oxidizing agent used to treat water. It kills bacteria by oxidizing them:

$\text{Cl}_2 + \text{H}_2\text{O} \rightarrow \text{HCl} + \text{HClO}$

The hypochlorous acid (HClO) oxidizes microorganisms in water.

Hydrogen Peroxide ($H_2O_2$): This compound releases oxygen, which oxidizes stains and kills germs:

$2\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2$

Hydrogen peroxide is used as a disinfectant in clinics and as a bleaching agent in textile factories in Tanzania.

Sulphur Dioxide ($SO_2$): Sulphur dioxide acts as a reducing agent but can also show oxidizing properties in certain reactions. It is used to preserve dried fruits and as a bleach in paper production.

What is Displacement?

Displacement occurs when a more reactive non-metal displaces a less reactive non-metal from its compound. The more electronegative element will replace the less electronegative one.

Reactivity Series of Non-Metals

The general order of reactivity for some non-metals (from most to least reactive):

Fluorine > Chlorine > Bromine > Iodine > Oxygen > Sulphur

Examples of Displacement Reactions

Chlorine displaces bromine and iodine:

$\text{2KBr(aq)} + \text{Cl}_2\text{(g)} \rightarrow 2\text{KCl(aq)} + \text{Br}_2\text{(l)}$

When chlorine gas is bubbled through potassium bromide solution, chlorine (more reactive) displaces bromine. The solution changes from colourless to orange-brown due to bromine.

$\text{2KI(aq)} + \text{Cl}_2\text{(g)} \rightarrow 2\text{KCl(aq)} + \text{I}_2\text{(s)}$

Chlorine also displaces iodine from potassium iodide, producing a purple iodine solution.

Bromine displaces iodine:

$\text{2KI(aq)} + \text{Br}_2\text{(l)} \rightarrow 2\text{KBr(aq)} + \text{I}_2\text{(s)}$

This reaction shows a visible colour change from colourless to purple as iodine forms.

Displacement of Hydrogen

Non-metals can also displace hydrogen from compounds:

$\text{CH}_4\text{(g)} + \text{Cl}_2\text{(g)} \rightarrow \text{CH}_3\text{Cl(g)} + \text{HCl(g)}$

In sunlight, chlorine displaces hydrogen from methane to form chloromethane and hydrogen chloride.

Question: When chlorine gas is passed through potassium iodide solution, what is observed and why?

Answer: The colourless solution turns purple. This happens because chlorine is more reactive than iodine. Chlorine displaces iodine from potassium iodide:

$2\text{KI(aq)} + \text{Cl}_2\text{(g)} \rightarrow 2\text{KCl(aq)} + \text{I}_2\text{(s)}$

The purple colour comes from iodine molecules ($I_2$) formed in the solution.

In Tanzania, chlorine is used in water treatment plants in Dar es Salaam, Mwanza, and Arusha to disinfect drinking water. The oxidizing property of chlorine kills harmful bacteria and viruses, making water safe to drink. Similarly, hydrogen peroxide is used in local clinics for wound disinfection and in hair salons for bleaching hair, thanks to its oxidizing property that breaks down coloured pigments and kills microorganisms.