Complete Guide to Sulphuric Acid Formulas

Detailed Explanations

1. Chemical Formula of Sulphuric Acid: H₂SO₄

The chemical formula H₂SO₄ represents sulphuric acid, one of the most important industrial chemicals worldwide. This formula indicates:

• 2 Hydrogen atoms (H)
• 1 Sulfur atom (S)
• 4 Oxygen atoms (O)

Molar Mass: 98.08 g/mol

2. Molecular Formula of Sulphuric Acid

The molecular formula is also H₂SO₄, which shows the actual number of each type of atom in one molecule. Unlike empirical formulas (which show simplest ratios), the molecular formula gives the complete composition.

3. Structural Formula

The structural arrangement shows sulfur as the central atom bonded to:

• Two hydroxyl groups (-OH)
• Two oxygen atoms with double bonds (=O)

Lewis Structure: The sulfur atom has 6 valence electrons and forms:

• 2 S-OH single bonds
• 2 S=O double bonds

4. Dilute Sulphuric Acid Formula

Formula: H₂SO₄ (aq)

Dilute sulphuric acid is simply H₂SO₄ dissolved in water. The (aq) notation indicates aqueous solution. Common concentrations include:

• Laboratory dilute: 1M to 6M (approximately 10-50% by mass)
• Battery acid: ~30-37% concentration

Dissociation in water:

• H₂SO₄ + H₂O → H₃O⁺ + HSO₄⁻ (First dissociation – complete)
• HSO₄⁻ + H₂O → H₃O⁺ + SO₄²⁻ (Second dissociation – partial)

5. Concentrated Sulphuric Acid

Formula: H₂SO₄ (98% concentration)

Concentrated sulphuric acid contains approximately 98% H₂SO₄ by mass with minimal water. It is:

• Highly corrosive and dehydrating
• Density: ~1.84 g/cm³
• Boiling point: 337°C

Safety Note: Always add acid to water, never water to acid, to prevent violent exothermic reactions.

6. Fuming Sulphuric Acid (Oleum)

Formula: H₂S₂O₇ or H₂SO₄·SO₃

Fuming sulphuric acid contains excess sulfur trioxide (SO₃) dissolved in H₂SO₄. When exposed to air, it releases SO₃ vapors, creating dense white fumes.

Common concentrations:

• 20% oleum = 104.5% H₂SO₄ equivalent
• 65% oleum = 114.6% H₂SO₄ equivalent

Formation: H₂SO₄ + SO₃ → H₂S₂O₇

7. Sulphurous Acid Formula: H₂SO₃

Important distinction: Sulphurous acid (H₂SO₃) is different from sulphuric acid (H₂SO₄).

Main differences:

8. Empirical vs. Molecular Formula

For sulphuric acid, both the empirical and molecular formulas are H₂SO₄ because the ratio of atoms (2:1:4) is already in its simplest form.

Physical and Chemical Properties

Physical Properties

• Appearance: Colorless, odorless, viscous liquid
• Density: 1.84 g/cm³ (concentrated)
• Melting point: 10.31°C
• Boiling point: 337°C
• Hygroscopic: Absorbs water from air

Chemical Properties

1. Strong acid: Completely dissociates in water
2. Dehydrating agent: Removes water from compounds
3. Oxidizing agent: Especially when hot and concentrated
4. Diprotic acid: Can donate two protons (H⁺ ions)

Common Chemical Reactions

1. With metals:

• Zn + H₂SO₄ (dilute) → ZnSO₄ + H₂↑

2. With bases (neutralization):

• H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

3. Dehydration of sugar:

• C₁₂H₂₂O₁₁ + H₂SO₄ → 12C + 11H₂O (black carbon forms)

4. With carbonates:

• H₂SO₄ + Na₂CO₃ → Na₂SO₄ + H₂O + CO₂↑

Industrial Production: Contact Process

Step 1: S + O₂ → SO₂

Step 2: 2SO₂ + O₂ ⇌ 2SO₃ (V₂O₅ catalyst, 450°C)

Step 3: SO₃ + H₂SO₄ → H₂S₂O₇ (oleum)

Step 4: H₂S₂O₇ + H₂O → 2H₂SO₄

Frequently Asked Questions on Sulphuric Acid Formulas

Q. What is the chemical formula of sulphuric acid?

The chemical formula of sulphuric acid is H₂SO₄. It consists of 2 hydrogen atoms, 1 sulfur atom, and 4 oxygen atoms, with a molar mass of 98.08 g/mol.

Q. What is the difference between sulphuric acid and sulphurous acid?

• Sulphuric acid (H₂SO₄): Strong acid with sulfur in +6 oxidation state, stable, used industrially
• Sulphurous acid (H₂SO₃): Weak acid with sulfur in +4 oxidation state, unstable, exists only in aqueous solution

The key difference is the oxidation state of sulfur and the number of oxygen atoms.

Q. What is the molecular formula of sulphuric acid?

The molecular formula is H₂SO₄, which represents the actual number of atoms in one molecule: 2 hydrogen, 1 sulfur, and 4 oxygen atoms. This is also the empirical formula since it’s already in the simplest ratio.

Q. What is dilute sulphuric acid formula?

Dilute sulphuric acid has the same chemical formula H₂SO₄ (aq), where (aq) denotes aqueous solution. It’s simply H₂SO₄ dissolved in water, typically with concentrations ranging from 10% to 50% by mass. The formula doesn’t change; only the concentration differs.

Q. What is fuming sulphuric acid (oleum)?

Fuming sulphuric acid, or oleum, is a solution of sulfur trioxide (SO₃) in sulphuric acid. Its formula can be written as H₂S₂O₇ or H₂SO₄·SO₃. It produces dense white fumes when exposed to moist air due to the release of SO₃ vapors. It’s stronger than 100% H₂SO₄.

Q. How does sulphuric acid dissociate in water?

Sulphuric acid is a diprotic acid that dissociates in two steps:

• First dissociation (complete): H₂SO₄ + H₂O → H₃O⁺ + HSO₄⁻
• Second dissociation (partial): HSO₄⁻ + H₂O ⇌ H₃O⁺ + SO₄²⁻

The first dissociation is complete, making H₂SO₄ a strong acid.

Q. Why is concentrated sulphuric acid dangerous?

Concentrated sulphuric acid (98% H₂SO₄) is extremely dangerous because it is:

• Highly corrosive: Burns skin and tissue severely
• Dehydrating agent: Removes water from organic materials
• Exothermic with water: Releases intense heat when mixed with water, causing spattering

Always add acid to water slowly, never the reverse.

Q. What is the structural formula of sulphuric acid?

The structural formula shows sulfur as the central atom bonded to four oxygen atoms: two with hydroxyl groups (-OH) and two with double bonds (=O). It can be represented as:

HO-SO₂-OH or with a complete Lewis structure showing all bonds and lone pairs. The sulfur atom uses sp³ hybridization.

Q. What are the main uses of sulphuric acid?

Sulphuric acid is the most widely produced industrial chemical with uses in:

• Fertilizer production: Manufacturing phosphate fertilizers (60-70% of production)
• Chemical manufacturing: Producing other acids, dyes, explosives
• Petroleum refining: Purifying petroleum products
• Metal processing: Pickling steel, extracting metals
• Batteries: Lead-acid batteries contain dilute H₂SO₄

Q. How is sulphuric acid produced industrially?

Sulphuric acid is produced by the Contact Process:

1. Burn sulfur or roast sulfide ores to produce SO₂
2. Oxidize SO₂ to SO₃ using oxygen and vanadium pentoxide (V₂O₅) catalyst at 450°C
3. Absorb SO₃ in concentrated H₂SO₄ to form oleum (H₂S₂O₇)
4. Dilute oleum with water to produce concentrated H₂SO₄

This process produces 98% pure sulphuric acid efficiently.

Tips for Students

1. Remember the formula: H₂SO₄ – “H-two-S-O-four”
2. Understand the difference: H₂SO₃ (sulphurous) vs. H₂SO₄ (sulphuric)
3. Practice calculations: Molar mass = 98.08 g/mol
4. Safety first: Always add acid to water
5. Know the reactions: With metals, bases, carbonates