Q2. What are oxidising agents?
NCERT Class 10 Science | Chapter: Carbon and Its Compounds / Chemical Reactions and Equations | Texcellency Book Series
✅ Answer: Oxidising agents are substances that oxidise other substances — by adding oxygen to them or by removing hydrogen from them — while getting reduced themselves in the process.
This is one of those definitions that sounds simple on the surface but hides a surprisingly deep concept underneath. A student who only writes the one-line definition gets 1 mark. A student who understands the electron transfer logic, the real-life examples, the distinction between oxidising and reducing agents, and can apply this to reactions — that student aces every related question. Let us build that complete understanding right now.
🏭 The Construction Site Analogy
Imagine a construction site. There is a crane operator whose only job is to take heavy materials from workers on the ground and lift them up. Every time the crane takes something away from a worker, that worker is left lighter — they have lost something.
In chemistry, oxidising agents are like that crane operator. They take electrons (or hydrogen) away from other substances. The substance that loses electrons is said to be oxidised. The oxidising agent, by taking those electrons, itself gets reduced.
This is the golden rule of redox chemistry:
- The oxidising agent → gets reduced (gains electrons)
- The substance being oxidised → loses electrons
They always work as a pair. You cannot have one without the other. This is why these reactions are called redox reactions — reduction and oxidation happening simultaneously.
🔵 The Two-Line Definition (Write This in Exams)
Oxidising agents are substances that:
- Oxidise other substances — by adding oxygen to them OR by removing hydrogen from them
- Get reduced themselves in the same reaction — by gaining electrons or losing oxygen
🔶 Understanding “Oxidation” First — To Understand Oxidising Agents
The word “oxidation” originally meant “reaction with oxygen.” Over time, chemists expanded the definition. Today, oxidation means any one of these three things:
🔵 Addition of oxygen — example: when iron (Fe) reacts with oxygen to form iron oxide (rust), iron is oxidised. Oxygen here is the oxidising agent.
🔵 Removal of hydrogen — example: when ethanol (CH₃CH₂OH) loses hydrogen atoms to become ethanal (CH₃CHO), ethanol is oxidised. The substance that removes the hydrogen is the oxidising agent.
🔵 Loss of electrons — example: when Fe²⁺ becomes Fe³⁺, it has lost an electron. It has been oxidised. The substance that accepted that electron is the oxidising agent.
All three definitions are valid. In Class 10, you will mostly encounter the first two. By Class 11-12, all three become important.
🔷 Real-Life Analogy — The Pickpocket
An oxidising agent behaves like a pickpocket in a crowded market.
The pickpocket (oxidising agent) goes around and steals valuables (electrons or hydrogen) from unsuspecting people (the substance being oxidised). The person who gets pickpocketed is poorer — they have lost something (they are oxidised). The pickpocket is richer — they have gained something (they are reduced).
Result: every pickpocketing event involves one person losing and one person gaining — simultaneously. That is exactly what happens in every redox reaction.
✅ Common Examples of Oxidising Agents (NCERT Class 10)
1. 🔴 Oxygen (O₂) — The Most Common Oxidising Agent
Oxygen is the original and most abundant oxidising agent in nature.
Example reaction: 2Mg + O₂ → 2MgO
Here, magnesium (Mg) is oxidised — it gains oxygen. Oxygen is the oxidising agent — it oxidises magnesium. Oxygen itself gets reduced (it gains electrons from magnesium).
Real-life examples of O₂ as an oxidising agent: 🔵 Rusting of iron — Fe + O₂ → iron oxide (rust) 🔵 Burning of fuels — carbon in fuel + O₂ → CO₂ (carbon is oxidised) 🔵 Respiration inside your body — glucose + O₂ → CO₂ + H₂O + energy (glucose is oxidised)
Oxygen is literally oxidising the food you eat right now to release the energy that keeps you alive. You are experiencing the work of an oxidising agent at this very moment.
2. 🔴 Potassium Permanganate — KMnO₄ (The Purple Powerhouse)
Potassium permanganate is one of the strongest and most commonly used oxidising agents in chemistry labs. It is a deep purple/violet coloured solid that dissolves in water to give an intensely purple solution.
How it works as an oxidising agent: KMnO₄ contains manganese in the +7 oxidation state — this is a very high and unstable oxidation state. Mn (+7) desperately wants to gain electrons and get reduced to a more stable state (usually Mn²⁺ in acidic solution, which is pale pink/colourless). In grabbing those electrons, it oxidises whatever substance is nearby.
Practical example in Class 10: KMnO₄ is used to oxidise ethanol (alcohol) → ethanoic acid (acetic acid / vinegar). The KMnO₄ is the oxidising agent here — it adds oxygen to the ethanol molecule.
Ethanol → (KMnO₄) → Ethanoic Acid
A visual clue in the lab: when KMnO₄ is used up (fully reduced), the purple colour disappears. So a colour change from purple to colourless indicates the oxidising agent has done its job. This is used in titrations.
Other uses of KMnO₄: 🔵 Disinfectant — kills bacteria and fungi (by oxidising their cell components) 🔵 Water treatment — purifies drinking water 🔵 Wound antiseptic — dilute KMnO₄ solution is used to clean infected wounds 🔵 Converts alcohols to acids and ketones in organic chemistry
3. 🔴 Potassium Dichromate — K₂Cr₂O₇ (The Orange Oxidiser)
Potassium dichromate is another powerful oxidising agent widely used in organic chemistry. It is an orange-coloured crystalline solid. Chromium here is in the +6 oxidation state — again, high and unstable — it wants to grab electrons and get reduced to Cr³⁺ (green).
Used for: 🔵 Oxidising primary alcohols → aldehydes or carboxylic acids 🔵 Oxidising secondary alcohols → ketones 🔵 Tanning of leather (industrial use) 🔵 Detecting alcohol in breathalyser tests — police use K₂Cr₂O₇ to test if a driver has been drinking. The orange dichromate turns green (Cr³⁺) when it oxidises the alcohol in breath. A colour change from orange to green = positive test for alcohol.
Memory hook: K₂Cr₂O₇ = Orange turns Green = Drunk driver caught!
4. 🔴 Dilute Sulphuric Acid (H₂SO₄) and Dilute Nitric Acid (HNO₃)
These acids can also act as oxidising agents in certain conditions, particularly concentrated nitric acid (HNO₃). They are used in various industrial and laboratory oxidation reactions.
5. 🔴 Hydrogen Peroxide — H₂O₂
Hydrogen peroxide is a mild oxidising agent. It is used as: 🔵 A bleaching agent for hair and textiles 🔵 An antiseptic (3% solution) to clean wounds 🔵 Rocket fuel oxidiser (concentrated H₂O₂)
Interesting fact: H₂O₂ can act as BOTH an oxidising agent AND a reducing agent depending on the reaction — making it a dual-natured compound.
📊 Oxidising Agents vs Reducing Agents — The Complete Comparison
| Feature | Oxidising Agent | Reducing Agent |
|---|---|---|
| What it does to others | Oxidises them (adds O₂ or removes H) | Reduces them (removes O₂ or adds H) |
| What happens to it | Gets reduced itself | Gets oxidised itself |
| Electron movement | Gains electrons | Loses electrons |
| Common examples | KMnO₄, K₂Cr₂O₇, O₂, H₂O₂ | H₂, Carbon (C), CO, Zn |
| Memory hook | OIL — Oxidising agents are In charge of making others Lose electrons | RIG — Reducing agents Itself Gives electrons |
The golden memory tool: OIL RIG 🔵 OIL = Oxidation Is Loss (of electrons) 🔵 RIG = Reduction Is Gain (of electrons)
🔶 A Classic Class 10 Reaction — Oxidising Agent in Action
Reaction: Copper oxide + Hydrogen → Copper + Water
CuO + H₂ → Cu + H₂O
🔵 CuO is the oxidising agent — it gives its oxygen to hydrogen, thereby oxidising hydrogen. 🔵 H₂ is the reducing agent — it takes oxygen from CuO, thereby reducing CuO back to copper metal.
You can see the copper being formed — the black CuO turns into shiny reddish-brown copper. This colour change is direct visual proof of the redox reaction in action.
🔷 Another Important Reaction — Oxidation of Ethanol
Ethanol + [O] → (KMnO₄ or K₂Cr₂O₇) → Ethanoic Acid
Here: 🔵 Ethanol is oxidised (it gains an oxygen / loses hydrogen) 🔵 KMnO₄ or K₂Cr₂O₇ is the oxidising agent — it provides the oxygen and gets reduced
This is directly relevant to the NCERT Class 10 chapter on Carbon and Its Compounds.
🎵 Rhyme to Remember Oxidising Agents
“An oxidising agent loves to take, Electrons or hydrogen — that’s what they make. They oxidise others while getting reduced, KMnO₄, K₂Cr₂O₇, O₂ — commonly used. OIL RIG is the trick to remember with care, Oxidation Is Loss, Reduction Is Gain — that’s the pair!”
🧩 Mnemonics
🔵 OIL RIG — Oxidation Is Loss, Reduction Is Gain (the most important redox mnemonic in chemistry) 🔵 “Oxidising agents GAIN to help others LOSE” — they gain electrons while making the other substance lose electrons 🔵 KMnO₄ = Purple Power — deep purple colour, powerful oxidiser, turns colourless when done 🔵 K₂Cr₂O₇ = Orange to Green — colour change signals it has oxidised something (used in breathalysers)
✅ Exam-Ready Answer
What are oxidising agents?
Oxidising agents are substances that oxidise other substances during a chemical reaction. They do this by:
- Adding oxygen to another substance, OR
- Removing hydrogen from another substance
In the process, the oxidising agent itself gets reduced — it gains electrons. This is why reactions involving oxidising agents are called redox reactions (reduction + oxidation occurring simultaneously).
Examples of oxidising agents: Potassium permanganate (KMnO₄), Potassium dichromate (K₂Cr₂O₇), Oxygen (O₂), Hydrogen peroxide (H₂O₂).
Key memory tool: OIL RIG — Oxidation Is Loss, Reduction Is Gain
📌 Key Points Checklist
✅ Oxidising agent = substance that oxidises others by adding O₂ or removing H ✅ Oxidising agent itself gets reduced in the same reaction ✅ OIL RIG = Oxidation Is Loss of electrons, Reduction Is Gain of electrons ✅ KMnO₄ = deep purple, powerful oxidising agent, turns colourless when reduced ✅ K₂Cr₂O₇ = orange, turns green when it oxidises a substance (used in breathalysers) ✅ O₂ = most common oxidising agent in nature (rusting, burning, respiration) ✅ H₂O₂ = mild oxidising agent, also used as bleach and antiseptic ✅ CuO + H₂ → Cu + H₂O: CuO is oxidising agent, H₂ is reducing agent ✅ Ethanol + KMnO₄ → Ethanoic Acid: KMnO₄ is the oxidising agent ✅ Reducing agents do the opposite — they reduce others while getting oxidised themselves
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