NCERT Class 10 Science | Chapter: Metals and Non-Metals | Texcellency Book Series

✅ Answer in Brief (For Quick Revision)

When non-metals combine with oxygen, they form acidic oxides — oxides that dissolve in water to produce acids, turning the solution acidic (pH less than 7) and turning blue litmus red. Examples: carbon + oxygen → CO₂ (dissolves in water → carbonic acid H₂CO₃). Sulphur + oxygen → SO₂ (dissolves in water → sulphurous acid H₂SO₃). This is in direct contrast to metal oxides, which are basic in nature (dissolve in water to form bases/alkalis).

🏭 The Personality Test Analogy — Metals vs Non-Metals

Imagine two groups of students in a school:

🔵 Group 1 — Metal students: Whenever they combine with oxygen, they become calm and cooperative — they form basic oxides that are compatible with acids, react with acids to form salts. They are the peacemakers — bases neutralise acids.

🔵 Group 2 — Non-metal students: Whenever they combine with oxygen, they become sharp and reactive — they form acidic oxides that produce acids when they meet water. They have a strong personality — sour, acidic, pH-lowering.

This personality difference — metals making basic oxides, non-metals making acidic oxides — is one of the most fundamental patterns in inorganic chemistry, and it runs through almost every chapter in Class 10 Science.

🔴 What is an Acidic Oxide? — The Definition

An acidic oxide is an oxide that: 🔵 Dissolves in water to form an acid (releases H⁺ ions in solution) 🔵 Turns blue litmus red (because the acid formed releases H⁺) 🔵 Has pH less than 7 in aqueous solution 🔵 Reacts with bases (alkalis) to form salt + water — like an acid does 🔵 Does NOT react with acids (because it is itself acidic — like charges repel)

All these properties come from the fundamental nature of non-metal oxides — their covalent bonding gives them the ability to react with water and produce hydrogen ions (H⁺).

🔶 Examples of Non-Metal Oxides — All Acidic

1. Carbon Dioxide (CO₂) — The Most Familiar Acidic Oxide:

🔵 Formation: C + O₂ → CO₂ (carbon burns in excess oxygen) 🔵 Reaction with water: CO₂ + H₂O → H₂CO₃ (carbonic acid) 🔵 Carbonic acid is a weak acid — it partially ionises: H₂CO₃ ⇌ H⁺ + HCO₃⁻ 🔵 pH of CO₂ solution: approximately 5.6 — mildly acidic 🔵 Real-life: CO₂ dissolved in rainwater makes natural rain slightly acidic (pH ~5.6). CO₂ dissolved in your blood forms carbonic acid — your body uses this to maintain blood pH. CO₂ dissolved in soft drinks (soda water) makes them slightly acidic and tingly. 🔵 Reaction with base: CO₂ + 2NaOH → Na₂CO₃ + H₂O (acidic oxide + base → salt + water)

2. Sulphur Dioxide (SO₂) — The Acid Rain Culprit:

🔵 Formation: S + O₂ → SO₂ (sulphur burning, also from volcanic eruptions and coal burning) 🔵 Reaction with water: SO₂ + H₂O → H₂SO₃ (sulphurous acid) 🔵 Sulphurous acid is a weak acid — pH of SO₂ solution is lower than CO₂ solution 🔵 Real-life: SO₂ from industrial emissions dissolves in rainwater → H₂SO₃ → acid rain. Responsible for damage to buildings (marble dissolves: CaCO₃ + H₂SO₃ → CaSO₃ + H₂O + CO₂), forests, and aquatic ecosystems. 🔵 Reaction with base: SO₂ + 2NaOH → Na₂SO₃ + H₂O

3. Sulphur Trioxide (SO₃) — The Stronger Acidic Oxide:

🔵 Formation: 2SO₂ + O₂ →(V₂O₅ catalyst, high temp)→ 2SO₃ (contact process for H₂SO₄ manufacturing) 🔵 Reaction with water: SO₃ + H₂O → H₂SO₄ (sulphuric acid — a strong acid!) 🔵 This is how industrial sulphuric acid is made — SO₃ absorbed in water gives H₂SO₄ 🔵 Real-life: sulphuric acid (battery acid, used in car batteries, industrial processes) is manufactured using SO₃ as the key intermediate 🔵 Acid rain contribution: SO₃ from industrial emissions + rainwater → H₂SO₄ in rain — highly damaging, more corrosive than H₂SO₃

4. Nitrogen Dioxide (NO₂) — Another Acid Rain Contributor:

🔵 Formation: N₂ + 2O₂ →(lightning, high temp in engines)→ 2NO₂ 🔵 Reaction with water: 3NO₂ + H₂O → 2HNO₃ + NO (nitric acid formed) 🔵 Real-life: NO₂ from vehicle exhaust and industrial processes + rainwater → HNO₃ → contributes to acid rain. Lightning strikes naturally produce NO₂ — this is actually how small amounts of fixed nitrogen enter the soil (a beneficial natural process). 🔵 NO₂ also causes photochemical smog in cities — the brown haze over heavily polluted cities contains NO₂.

5. Phosphorus Pentoxide (P₄O₁₀) — A Strongly Acidic Oxide:

🔵 Formation: P₄ + 5O₂ → P₄O₁₀ (phosphorus burning in excess oxygen) 🔵 Reaction with water: P₄O₁₀ + 6H₂O → 4H₃PO₄ (phosphoric acid) 🔵 P₄O₁₀ is a powerful desiccant (drying agent) — it absorbs water so aggressively that it is used in labs to dry gases and solvents 🔵 Real-life: phosphoric acid (H₃PO₄) is used in fertilisers, cola drinks (gives the slight tangy taste), and rust-removal products

6. Silicon Dioxide (SiO₂) — An Acidic Oxide That Does NOT Dissolve in Water:

🔵 SiO₂ (quartz, sand, glass) is a non-metal oxide — it IS acidic in nature 🔵 BUT it does not dissolve in water — it is a solid with a giant covalent structure 🔵 It DOES react with strong bases: SiO₂ + 2NaOH →(high temp)→ Na₂SiO₃ + H₂O (sodium silicate) 🔵 This is why glassware (SiO₂) is attacked by concentrated NaOH — the acidic SiO₂ reacts with the base 🔵 SiO₂ reacts with basic oxides at high temperature: SiO₂ + CaO →(high temp)→ CaSiO₃ (used in metallurgy)

🔷 The Contrast — Metal Oxides Are Basic

To fully understand acidic oxides, you must contrast them with basic oxides (metal oxides):

Metal Oxides = Basic Oxides: 🔵 CaO + H₂O → Ca(OH)₂ (calcium hydroxide — slaked lime — a strong base) 🔵 Na₂O + H₂O → 2NaOH (sodium hydroxide — strong base) 🔵 MgO + H₂O → Mg(OH)₂ (magnesium hydroxide — mild base, used in antacids) 🔵 Fe₂O₃ + acid → iron salt + water (basic oxide reacts with acid) 🔵 CuO + acid → copper salt + water (see our copper vessel cleaning post!)

Non-Metal Oxides = Acidic Oxides: 🔵 CO₂ + H₂O → H₂CO₃ (carbonic acid — weak acid) 🔵 SO₂ + H₂O → H₂SO₃ (sulphurous acid — weak acid) 🔵 SO₃ + H₂O → H₂SO₄ (sulphuric acid — strong acid) 🔵 NO₂ + H₂O → HNO₃ (nitric acid — strong acid)

The Golden Rule: Metal + Oxygen → Basic Oxide. Non-metal + Oxygen → Acidic Oxide.

🔴 The Special Cases — Neutral Oxides and Amphoteric Oxides

The examiner may sometimes ask about exceptions. Knowing these earns bonus marks.

Neutral Oxides (neither acidic nor basic): 🔵 CO (carbon monoxide) — a non-metal oxide that does NOT react with water to form any acid. Neutral oxide. Extremely toxic (see our carbon compounds and fuels post). 🔵 NO (nitric oxide) — another neutral non-metal oxide. Does not react with water under normal conditions. 🔵 H₂O (water) — technically an oxide of hydrogen — neutral.

These are neutral oxides — non-metal oxides that are exceptions to the “all non-metal oxides are acidic” rule. They neither form acids nor bases with water.

Amphoteric Oxides (both acidic AND basic): 🔵 Al₂O₃ (aluminium oxide) — reacts with BOTH acids AND bases: With acid: Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O (behaves as a base) With base: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (behaves as an acid) 🔵 ZnO (zinc oxide) — also amphoteric: With acid: ZnO + H₂SO₄ → ZnSO₄ + H₂O With base: ZnO + 2NaOH → Na₂ZnO₂ + H₂O 🔵 These come from metals (Al, Zn) but have acidic character too — hence “amphoteric” (from Greek “amphi” = both)

For Class 10 board exam purposes: 🔵 Standard answer = non-metal oxides are acidic ✅ 🔵 Exception worth knowing = CO and NO are neutral (non-metal oxides but neutral) ✅ 🔵 Amphoteric = Al₂O₃, ZnO — metal oxides that react with both acids and bases ✅

🔶 Real-World Application — Acid Rain: Non-Metal Oxides Causing Global Environmental Damage

This is one of the most important real-world applications of this chemistry — and it directly connects your Class 10 knowledge to current environmental issues.

What causes acid rain? 🔵 Burning fossil fuels (coal, petroleum) in power stations, factories, and vehicles releases SO₂ and NO₂ into the atmosphere 🔵 Volcanic eruptions also release SO₂ naturally 🔵 These acidic non-metal oxides dissolve in rainwater: SO₂ + H₂O → H₂SO₃ | SO₃ + H₂O → H₂SO₄ | NO₂ + H₂O → HNO₃ 🔵 Normal rain pH = 5.6 (slightly acidic due to natural CO₂). Acid rain pH = 4.2 to 4.4 — significantly more acidic

What damage does acid rain cause? 🔵 Buildings and monuments: The Taj Mahal is slowly being damaged by acid rain — sulphuric acid dissolves the marble (CaCO₃): CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂. CaSO₄ (gypsum) is white and powdery — it washes off in rain, slowly eroding the marble surface. This is called “marble cancer.” 🔵 Forests: Acid rain leaches essential minerals from soil, weakens trees, directly damages leaves 🔵 Aquatic ecosystems: Lakes and rivers become acidic → fish and aquatic life die 🔵 Soil: Destroys soil microbial communities, reduces agricultural productivity 🔵 Metal structures: Acid rain accelerates corrosion of iron and steel bridges, buildings

The connection: Every time SO₂ or NO₂ enters the atmosphere from a factory chimney or a car exhaust, it is a non-metal oxide — and it follows the exact same chemistry you are studying: non-metal oxide + water → acid. This is not just a classroom concept — it is an ongoing global environmental crisis.

🔷 Why Non-Metal Oxides Are Acidic — The Chemistry Reason

Non-metal oxides are acidic because of the nature of their bonding and their ability to react with water:

🔵 Non-metals have high electronegativity — they pull electron density strongly toward themselves 🔵 When a non-metal oxide dissolves in water, the non-metal’s high electronegativity polarises the O–H bonds in water, making it easier for H⁺ to be released 🔵 The result: H⁺ ions in solution → acidic pH

In contrast, metal oxides contain ionic bonds (Metal²⁺ O²⁻). When they dissolve in water, the O²⁻ ion accepts H⁺ from water → forms OH⁻ → basic solution.

🔵 Non-metal oxide + H₂O → releases H⁺ → acidic 🔵 Metal oxide + H₂O → releases OH⁻ → basic

This is the fundamental electronic reason behind the entire metal oxide vs non-metal oxide distinction.

📊 Complete Summary Table

Carbon dioxide CO₂: Non-metal oxide → Acidic → CO₂ + H₂O → H₂CO₃ (carbonic acid) → Real life: fizzy drinks, rain acidification Sulphur dioxide SO₂: Non-metal oxide → Acidic → SO₂ + H₂O → H₂SO₃ (sulphurous acid) → Real life: acid rain, air pollution Sulphur trioxide SO₃: Non-metal oxide → Acidic → SO₃ + H₂O → H₂SO₄ (sulphuric acid) → Real life: H₂SO₄ manufacture, severe acid rain Nitrogen dioxide NO₂: Non-metal oxide → Acidic → 3NO₂ + H₂O → 2HNO₃ + NO → Real life: acid rain, smog Carbon monoxide CO: Non-metal oxide → NEUTRAL → does not react with H₂O → Real life: toxic gas, incomplete combustion product Calcium oxide CaO: Metal oxide → Basic → CaO + H₂O → Ca(OH)₂ → Real life: slaked lime, cement, antacid Sodium oxide Na₂O: Metal oxide → Basic → Na₂O + H₂O → 2NaOH → Real life: caustic soda production Aluminium oxide Al₂O₃: Metal oxide → Amphoteric → reacts with both acids and bases → Real life: protective oxide layer on aluminium

🎵 Rhyme to Remember

“Non-metal plus oxygen — acidic is the game, CO₂, SO₂, NO₂ — they’re all playing the same!* Dissolve them in water — an acid you will get,* H₂CO₃, H₂SO₃ — pH drops, don’t forget!* Metal plus oxygen — basic is the rule,* CaO, Na₂O, MgO — base-making school!* Acid rain is SO₂ and NO₂ in the sky,* Dissolving in rainwater as clouds float by,* Taj Mahal is suffering — marble cancer they say,* Non-metal oxide chemistry is making it decay!”*

🧩 Mnemonics

🔵 “NON-METALS = Negatively Oxide Nature — acidic” vs “METALS = Make Excellent Basic Alkaline Landings — basic.” 🔵 “CO₂ → H₂CO₃. SO₂ → H₂SO₃. SO₃ → H₂SO₄. NO₂ → HNO₃.” — four key non-metal oxide + water reactions in a chain. The oxide formula tells you which acid forms: just add H₂O. 🔵 “Acid rain = SO₂ + NO₂ from factories and cars + rainwater = H₂SO₃ + HNO₃ = Taj Mahal damage.” — the complete acid rain story in one memory chain. 🔵 “CO = Neutral. CO₂ = Acidic. Carbon makes BOTH — know which is which.” — the two carbon oxides with opposite behaviours. 🔵 “Amphoteric = Al₂O₃ and ZnO — ALuminium and ZiNc react with BOTH acids and bases.” — AL-ZN = amphoteric pair.

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

What type of oxides are formed when non-metals combine with oxygen?

When non-metals combine with oxygen, they form acidic oxides.

Reason: Non-metal oxides dissolve in water to produce acids — they release H⁺ ions in solution, making the solution acidic (pH less than 7) and turning blue litmus red.

Examples:

🔵 Carbon + Oxygen → CO₂ (carbon dioxide) — acidic oxide CO₂ + H₂O → H₂CO₃ (carbonic acid)

🔵 Sulphur + Oxygen → SO₂ (sulphur dioxide) — acidic oxide SO₂ + H₂O → H₂SO₃ (sulphurous acid)

🔵 Sulphur + Oxygen → SO₃ (sulphur trioxide) — acidic oxide SO₃ + H₂O → H₂SO₄ (sulphuric acid)

Contrast with Metal Oxides: Metal oxides (e.g. CaO, Na₂O, MgO) are basic oxides — they dissolve in water to form bases (hydroxides): CaO + H₂O → Ca(OH)₂.

Exception — Neutral Oxides: CO (carbon monoxide) and NO (nitric oxide) are non-metal oxides that are neutral — they do not react with water to form acids or bases.

Environmental significance: SO₂ and NO₂ released from burning fossil fuels dissolve in rainwater to form H₂SO₃, H₂SO₄, and HNO₃ — causing acid rain, which damages buildings (including the Taj Mahal), forests, and aquatic ecosystems.

📌 Key Points Checklist

✅ Non-metals + oxygen → acidic oxides (dissolve in water to form acids) ✅ Metal + oxygen → basic oxides (dissolve in water to form bases) ✅ CO₂ + H₂O → H₂CO₃ (carbonic acid — weak) ✅ SO₂ + H₂O → H₂SO₃ (sulphurous acid — weak, acid rain) ✅ SO₃ + H₂O → H₂SO₄ (sulphuric acid — strong, severe acid rain) ✅ NO₂ + H₂O → HNO₃ + NO (nitric acid — strong, acid rain) ✅ P₄O₁₀ + H₂O → H₃PO₄ (phosphoric acid) ✅ Neutral oxides (exceptions): CO and NO — non-metal oxides that are neither acidic nor basic ✅ Amphoteric oxides: Al₂O₃ and ZnO — react with BOTH acids and bases ✅ Acid rain: SO₂ + NO₂ from fossil fuel burning → H₂SO₃ + H₂SO₄ + HNO₃ in rain → damages Taj Mahal (marble cancer), forests, lakes ✅ Acidic oxide + base → salt + water (e.g. CO₂ + 2NaOH → Na₂CO₃ + H₂O) ✅ Basic oxide + acid → salt + water (e.g. CuO + H₂SO₄ → CuSO₄ + H₂O)

📚 Want ALL of Class 10 Science Explained This Way? Every chapter. Every concept. Every NCERT question — with analogies, rhymes, mnemonics, and real-life examples.