Sulphuric Acid (H₂SO₄)

ICSE Class 10 Chemistry • Chapter 11

1. Industrial Manufacture - Contact Process

Step 1: Burning of Sulphur

S + O₂ → SO₂

Step 2: Catalytic Oxidation

2SO₂ + O₂ ⇌ 2SO₃

Conditions: 450°C, V₂O₅ catalyst, 2-3 atm

Step 3: Absorption in Oleum

SO₃ + H₂SO₄ → H₂S₂O₇ (oleum)

Step 4: Dilution

H₂S₂O₇ + H₂O → 2H₂SO₄

Why not directly SO₃ + H₂O?

The reaction is highly exothermic and forms acid mist which is difficult to condense. Hence, absorbed in conc. H₂SO₄ to form oleum first.

2. Physical Properties

Property	Description
Appearance	Colourless, oily liquid
Density	1.84 g/cm³ (heavier than water)
Boiling Point	338°C (high, non-volatile)
Solubility	Highly soluble in water (exothermic)

ALWAYS add acid to water, NEVER water to acid!

Adding water to acid causes violent splashing due to rapid heat generation.

3. Chemical Properties

A. As a Dilute Acid

With Metals: Zn + H₂SO₄(dil) → ZnSO₄ + H₂↑

With Metal Oxides: CuO + H₂SO₄ → CuSO₄ + H₂O

With Metal Hydroxides: NaOH + H₂SO₄ → NaHSO₄ + H₂O

With Carbonates: Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂↑

With Sulphites: Na₂SO₃ + H₂SO₄ → Na₂SO₄ + H₂O + SO₂↑

B. As an Oxidising Agent (Conc. Hot)

Conc. H₂SO₄ acts as oxidising agent when hot:

H₂SO₄ → H₂O + SO₂ + [O] (nascent oxygen)

With Carbon: C + 2H₂SO₄ → CO₂ + 2H₂O + 2SO₂

With Sulphur: S + 2H₂SO₄ → 3SO₂ + 2H₂O

With Copper: Cu + 2H₂SO₄(hot conc) → CuSO₄ + 2H₂O + SO₂↑

C. As a Dehydrating Agent

Removes water from substances (not just drying, but chemical removal of H and O as H₂O)

With Sugar:

C₁₂H₂₂O₁₁ → 12C + 11H₂O (charred black carbon left)

With Blue Vitriol:

CuSO₄·5H₂O → CuSO₄ + 5H₂O (blue → white)

With Formic Acid:

HCOOH → H₂O + CO

With Oxalic Acid:

H₂C₂O₄ → H₂O + CO + CO₂

Test for dehydration of sugar:

Add conc. H₂SO₄ to sugar → Black mass swells up (carbon) with steaming

D. Non-Volatile Nature

H₂SO₄ has high boiling point (338°C) → can displace volatile acids from their salts.

NaCl + H₂SO₄ → NaHSO₄ + HCl↑

NaNO₃ + H₂SO₄ → NaHSO₄ + HNO₃↑

4. Tests for Sulphate Ions

Test	Observation
BaCl₂ solution + dil. HCl	White precipitate of BaSO₄ (insoluble in dil. HCl)
Lead acetate solution	White precipitate of PbSO₄

BaCl₂ + H₂SO₄ → BaSO₄↓ + 2HCl

White precipitate insoluble in dil. HCl or HNO₃

5. Uses of Sulphuric Acid

Manufacture of fertilisers (superphosphate, ammonium sulphate)
Petroleum refining
In lead-acid batteries (storage batteries)
Manufacture of pigments, paints, dyes
In metallurgy (pickling of metals)
Manufacture of chemicals (HCl, HNO₃)
As a laboratory reagent

Called "King of Chemicals" due to its extensive industrial use.

Quick Reference

Property	Role	Example Reaction
Acidic	H⁺ donor	With Zn → H₂
Oxidising (hot conc.)	Provides [O]	With Cu → SO₂
Dehydrating	Removes H₂O	With sugar → Carbon
Non-volatile	Displaces volatile acids	With NaCl → HCl

Exam Practice (PYQ Trends)

PYQ: 2023

BOARD Give the equations for the Contact Process for manufacture of sulphuric acid. State the catalyst used.

PYQ: 2022

BOARD Explain the dehydrating action of conc. H₂SO₄ with sugar. Write equation.