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MHT-CET Chemistry · Redox Reactions

Oxidising and Reducing Agents, and Acidic, Basic and Neutral Oxides

An oxidising agent takes electrons and is itself reduced; a reducing agent gives electrons and is itself oxidised; and an oxide is acidic, basic, amphoteric or neutral depending on the element it is made from.

All Redox Reactions notesMHT-CET Chemistry strategy

Why this matters

6 PYQs, none HARD. Four are about agents — the weakest reducing agent, which element tends to be reduced, what tin can reduce, the catalyst for KClO₃ — and two classify an oxide. Two cards, and the second is a table to learn.

Concept 1 of 2: Oxidising and Reducing Agents and Their Strength

A strong reducing agent loses electrons easily; a strong oxidising agent grabs them. Metals on the left of the table are reducing agents, non-metals like oxygen and the halogens are oxidising agents, and a species that has already gained electrons — F⁻, Cl⁻ — is a very poor reducing agent. The standard reduction potential ranks them: the more positive E°, the stronger the oxidising agent.

Definition

  • Reducing agent is oxidised (loses e⁻); oxidising agent is reduced (gains e⁻).
  • Strongest reducing agent: Li (most negative E°). Weakest reducing agent: F⁻ (F₂ is the strongest oxidising agent, so F⁻ holds its electron hardest).
  • Tends to be reduced: non-metals with high electron affinity — O, the halogens. Metals (Mg, Ni, Cu) tend to be oxidised.
  • A metal reduces a species with a higher E°: Sn (E° −0.14 V) reduces I₂ (+0.54 V) to I⁻.
  • KClO₃ decomposition: 2KClO₃ → 2KCl + 3O₂ with MnO₂ as catalyst (an internal redox: Cl +5 → −1, O −2 → 0).

Can A reduce B?

A reduces B if EB∘>EAn+/A∘\text{A reduces B if } E^\circ_{\text{B}} > E^\circ_{\text{A}^{n+}/\text{A}}

Worked example

Which is the weakest reducing agent: Li, Li⁺, F₂, F⁻?
Practice this conceptself-check · 3 quick reps

The same idea in a real exam question:

MHT-CET · 2025 · 25 April Shift I · Q53Moderate

Example 1 · Redox Reactions · Reducing/Oxidizing Agents and Acidic/Basic Oxides

Which of the following species acts as a weakest reducing agent?

Confusing the strongest oxidising agent with the weakest reducing agent

F₂ is the strongest oxidising agent; its partner F⁻ is the weakest reducing agent. The question may offer both — read which one it asks for.
Drill 3 more on oxidising and reducing agents and their strength

Concept 2 of 2: Acidic, Basic, Amphoteric and Neutral Oxides

An oxide's character follows the element: a metal oxide dissolves in acid (basic), a non-metal oxide in its higher state is the anhydride of an acid (acidic), a few in the middle do both (amphoteric), and a handful of low oxides of non-metals do neither (neutral).

Definition

  • Basic: metal oxides — Na₂O, CaO, MgO.
  • Acidic: non-metal oxides that form an acid with water — N₂O₅ (HNO₃), SO₃ (H₂SO₄), CO₂, P₄O₁₀.
  • Amphoteric: react with both acids and bases — Al₂O₃, ZnO.
  • Neutral: CO, NO, N₂O, H₂O.
OxideCharacterWhy
CaOBasicMetal oxide; CaO + 2HCl → CaCl₂ + H₂OQ
N₂O₅AcidicAnhydride of HNO₃Q
SO₃AcidicAnhydride of H₂SO₄
Al₂O₃AmphotericDissolves in HCl and in NaOH
CO, NO, N₂ONeutralNo acid or base forms with water
The trap: N₂O₅ is acidic, but N₂O and NO are neutral — the oxidation state decides.
Higher oxidation state of a non-metal → more acidic oxide.
Practice this conceptself-check · 3 quick reps

The same idea in a real exam question:

MHT-CET · 2023 · 16th May Shift 2 · Q81Easy

Example 2 · Redox Reactions · Reducing/Oxidizing Agents and Acidic/Basic Oxides

Identify basic oxide from following.
Drill 1 more on acidic, basic, amphoteric and neutral oxides

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Formulas (1)

Reference tables (1)

Acidic, Basic, Amphoteric and Neutral Oxides5 rows
OxideCharacterWhy
CaOBasicMetal oxide; CaO + 2HCl → CaCl₂ + H₂OQ
N₂O₅AcidicAnhydride of HNO₃Q
SO₃AcidicAnhydride of H₂SO₄
Al₂O₃AmphotericDissolves in HCl and in NaOH
CO, NO, N₂ONeutralNo acid or base forms with water
The trap: N₂O₅ is acidic, but N₂O and NO are neutral — the oxidation state decides.
Higher oxidation state of a non-metal → more acidic oxide.

Watch out for (1)

Test yourself on Redox Reactions

15 past MHT-CET questions from this chapter, timed at 14 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.

Take the Redox Reactions chapter testDrill all 6 questions