NCERT Class 10 Science | Chapter: Carbon and Its Compounds | Texcellency Book Series

✅ Answer: Because Oxygen is Added to Ethanol — and Hydrogen is Removed — Both of Which Define Oxidation

The conversion of ethanol (CH₃CH₂OH) to ethanoic acid (CH₃COOH) is an oxidation reaction because:

🔵 Reason 1 — Addition of oxygen: Ethanol gains an oxygen atom in the process. The -OH group of ethanol becomes the -COOH group of ethanoic acid. An extra oxygen atom has been added to the carbon skeleton. Addition of oxygen = oxidation. 🔵 Reason 2 — Removal of hydrogen: Simultaneously, two hydrogen atoms are removed from the ethanol molecule. Removal of hydrogen = oxidation.

Both these changes — gaining oxygen AND losing hydrogen — are the classic definitions of oxidation. This reaction satisfies both. That is why it is definitively and unambiguously called an oxidation reaction.

🏭 The Renovation Analogy — Upgrading a House

Think of ethanol as a simple house with a basic front door (the -OH group). Now imagine a renovation team arrives (the oxidising agent — KMnO₄ or K₂Cr₂O₇) and does two things:

🔵 Adds a new room (adds an oxygen atom) — the house now has an extra oxygen-containing structure 🔵 Removes two windows (removes two hydrogen atoms) — the house becomes leaner in hydrogen

The result? A completely different, upgraded structure — ethanoic acid (with a -COOH group instead of a simple -OH). This renovation process — adding oxygen and removing hydrogen — is exactly what oxidation means in organic chemistry.

🔶 Let Us Look at the Molecules — What Actually Changes

This is where most students lose marks — they write “oxygen is added” without explaining WHERE and HOW. Let us be precise.

Ethanol (the starting material):

Structure: CH₃ — CH₂ — OH Functional group: -OH (hydroxyl group) Carbon count: 2 carbons What it looks like chemically: the carbon attached to -OH has 2 hydrogen atoms bonded to it (it is a -CH₂OH group)

Ethanoic Acid (the product):

Structure: CH₃ — COOH Functional group: -COOH (carboxyl group) Carbon count: still 2 carbons (same carbon skeleton — nothing added or removed from the chain) What it looks like chemically: the same carbon now has NO hydrogen atoms — it is bonded to =O and -OH (which together form -COOH)

What changed between them?

🔵 The -CH₂OH group of ethanol became the -COOH group of ethanoic acid 🔵 To go from -CH₂OH → -COOH: one oxygen atom was ADDED and two hydrogen atoms were REMOVED 🔵 Net change: +1 oxygen, -2 hydrogen 🔵 This is the definition of oxidation — oxygen in, hydrogen out

🔴 The Chemical Equation — With Oxidising Agent

This reaction does NOT happen on its own. It needs an oxidising agent — a substance that provides the oxygen and accepts the hydrogen.

The oxidising agents used in Class 10 for this reaction are: 🔵 Alkaline KMnO₄ (potassium permanganate) — deep purple, turns colourless when reduced 🔵 Acidified K₂Cr₂O₇ (potassium dichromate) — orange, turns green when reduced

The reaction:

CH₃CH₂OH + [O] → CH₃COOH + H₂O

(Ethanol + Oxygen from oxidising agent → Ethanoic acid + Water)

The [O] in the equation represents the oxygen supplied by the oxidising agent (KMnO₄ or K₂Cr₂O₇).

Expanded version with KMnO₄:

CH₃CH₂OH + 2[O] →(KMnO₄)→ CH₃COOH + H₂O

The KMnO₄ provides the [O] and itself gets reduced (Mn goes from +7 to +2 — the purple colour disappears). This colour change — purple to colourless — is visible proof the oxidation of ethanol has occurred.

🔷 The OIL RIG Rule — Why This is Definitively Oxidation

OIL RIG is the most important memory tool in redox chemistry:

🔵 OIL = Oxidation Is Loss (of electrons / of hydrogen) 🔵 RIG = Reduction Is Gain (of electrons / of oxygen)

Now apply it to ethanol → ethanoic acid:

🔵 Ethanol loses 2 hydrogen atoms → OIL → ethanol is oxidised ✅ 🔵 Ethanol gains 1 oxygen atom → Wait — gaining oxygen is also oxidation? YES — in organic chemistry, gaining oxygen = being oxidised (because oxygen is electronegative; bonding with oxygen effectively means losing electron density)

Both criteria confirm: ethanol is oxidised. The reaction is an oxidation reaction.

🔶 The Real-Life Connection — Vinegar from Wine

This reaction is not just a textbook abstraction. It happens in your kitchen.

Wine left open → turns sour → becomes vinegar

Here is what is happening chemically: 🔵 Wine contains ethanol (alcohol — the same C₂H₅OH from your textbook) 🔵 When wine is exposed to air, bacteria called Acetobacter use the oxygen in air to oxidise the ethanol 🔵 Ethanol + O₂ (from air, via bacteria) → Ethanoic acid (acetic acid = the main component of vinegar) 🔵 This is exactly the same oxidation reaction — just happening biologically instead of chemically

So the sour taste of vinegar is the taste of ethanoic acid — produced by the biological oxidation of ethanol. This is why wine left open goes sour and why intentionally produced vinegar is made through controlled fermentation and oxidation of ethanol.

This real-life example is gold in an exam answer — it shows you understand the chemistry beyond the formula.

🔴 Two Definitions of Oxidation — Both Satisfied Here

In Class 10, oxidation is defined in two ways. This reaction satisfies BOTH:

Any one of these two is sufficient to call a reaction an oxidation reaction. This reaction satisfies both — making it an especially clear-cut example of oxidation.

🔶 Structural Comparison — Side by Side

🎵 Rhyme to Remember

“Ethanol starts with -OH so fine, Smells like spirit, tastes like wine, Add an oxygen, take two H away, Ethanoic acid is formed that day! The -OH becomes -COOH — see the change? Oxygen added — oxidation’s the name! KMnO₄ is the agent that does the deed, Purple turns colourless — oxidation guaranteed!”

🧩 Mnemonics

🔵 “ETHANOL LOSES to become ETHANOIC” — ethanol loses hydrogen (and gains oxygen) to become ethanoic acid. Loss = oxidation (OIL). 🔵 “-OH → -COOH = One O In, Two H Out” — the functional group change tells you everything: one oxygen in, two hydrogens out = oxidation. 🔵 “Wine goes sour = ethanol gets oxidised” — the real-life vinegar story anchors the chemistry in memory. 🔵 “Purple KMnO₄ disappears = oxidation has happened” — the colour change is your visible confirmation. 🔵 OIL RIG: Oxidation Is Loss (of H), Reduction Is Gain (of O from the agent’s perspective)

✅ Exam-Ready Answer (Write This in Board Exam)

Why is the conversion of ethanol to ethanoic acid an oxidation reaction?

The conversion of ethanol (CH₃CH₂OH) to ethanoic acid (CH₃COOH) is an oxidation reaction because:

Reason 1 — Addition of Oxygen: During this conversion, an oxygen atom is added to the ethanol molecule. The -OH (hydroxyl) group of ethanol is converted into the -COOH (carboxyl) group of ethanoic acid. The number of oxygen atoms increases from 1 (in ethanol) to 2 (in ethanoic acid). Addition of oxygen to a substance is defined as oxidation.

Reason 2 — Removal of Hydrogen: Simultaneously, two hydrogen atoms are removed from the ethanol molecule during this conversion. Removal of hydrogen from a substance is also defined as oxidation.

Since both criteria for oxidation are satisfied — oxygen is added AND hydrogen is removed — this reaction is definitively an oxidation reaction.

Chemical equation: CH₃CH₂OH + 2[O] →(KMnO₄ or K₂Cr₂O₇)→ CH₃COOH + H₂O

The oxidising agent used is either alkaline KMnO₄ (potassium permanganate) or acidified K₂Cr₂O₇ (potassium dichromate). These agents supply the [O] and get reduced in the process.

Real-life example: This is the same reaction that turns wine into vinegar — ethanol in wine gets oxidised to ethanoic acid (acetic acid) by bacteria in the presence of oxygen.

📌 Key Points Checklist

✅ Oxidation = addition of oxygen OR removal of hydrogen (both satisfied here) ✅ Ethanol (CH₃CH₂OH) → Ethanoic acid (CH₃COOH): gains 1 oxygen, loses 2 hydrogen ✅ Functional group change: -OH (hydroxyl) → -COOH (carboxyl) ✅ Equation: CH₃CH₂OH + 2[O] → CH₃COOH + H₂O ✅ Oxidising agents used: KMnO₄ (purple → colourless) or K₂Cr₂O₇ (orange → green) ✅ OIL RIG: Oxidation Is Loss (of H), Reduction Is Gain (of electrons by oxidising agent) ✅ Real-life example: wine turning sour to vinegar = ethanol being oxidised to ethanoic acid ✅ Ethanol = neutral (wine/spirit smell) • Ethanoic acid = acidic (sour vinegar smell) ✅ Colour change of KMnO₄ (purple → colourless) is visible proof of oxidation occurring ✅ This is an organic oxidation reaction — one of the most important in Class 10 Carbon chapter

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