Yes, dilute sulphuric acid is unequivocally a strong acid. It dissociates almost completely in water to release hydrogen ions.
Sulphuric acid (H₂SO₄) is renowned as a strong mineral acid. The strength of an acid is determined by its ability to dissociate, or ionize, in an aqueous solution, releasing hydrogen ions (H⁺). A strong acid dissociates fully, or nearly fully, in water. Even when diluted, sulphuric acid retains this fundamental characteristic.
Understanding Acid Strength and Dilution
The term "strong acid" refers to the acid's inherent chemical property to ionize. Dilution, on the other hand, refers to the concentration of the acid in a solvent, typically water.
- Complete Dissociation: In its first dissociation step, sulphuric acid completely ionizes:
H₂SO₄ (aq) → H⁺ (aq) + HSO₄⁻ (aq)
This complete ionization is the defining feature of a strong acid. The second dissociation step, HSO₄⁻ (aq) ⇌ H⁺ (aq) + SO₄²⁻ (aq), is also significant, although not 100% complete, further contributing to its strength. - Impact of Dilution: Dilution does not change the fact that sulphuric acid is a strong acid; it simply lowers the concentration of the acid particles (and thus H⁺ ions) per unit volume. However, it's important to note that dilute sulphuric acid is a stronger acid than concentrated sulphuric acid in terms of the number of free hydrogen ions (H⁺) available in the solution. This is because dilution provides more water molecules to facilitate the dissociation process, leading to a greater effective concentration of H⁺ ions compared to highly concentrated solutions where H₂SO₄ molecules might not fully dissociate due to a lack of available water or competing intermolecular interactions.
Properties of Dilute Sulphuric Acid
Dilute sulphuric acid exhibits the characteristic properties of strong acids:
- Highly Corrosive: Even when dilute, it can cause severe chemical burns upon contact with skin and can damage many materials.
- Reacts with Metals: It readily reacts with many metals above hydrogen in the reactivity series to produce hydrogen gas and a metal sulphate.
- Example: Mg(s) + H₂SO₄ (aq) → MgSO₄ (aq) + H₂(g)
- Reacts with Bases/Alkalies: It neutralizes bases to form salt and water.
- Example: 2NaOH (aq) + H₂SO₄ (aq) → Na₂SO₄ (aq) + 2H₂O (l)
- Reacts with Carbonates: It reacts with metal carbonates to produce carbon dioxide gas, water, and a metal sulphate.
- Example: CaCO₃ (s) + H₂SO₄ (aq) → CaSO₄ (aq) + H₂O (l) + CO₂(g)
Dilute vs. Concentrated Sulphuric Acid: A Comparison
While both are strong acids, their properties and applications differ significantly due to concentration.
| Feature | Dilute Sulphuric Acid (e.g., < 20%) | Concentrated Sulphuric Acid (e.g., > 90%) |
|---|---|---|
| Acidity | Exhibits strong acidic properties due to readily available H⁺ ions. | Also a strong acid, but its dehydrating/oxidizing properties are more pronounced. |
| H⁺ Availability | Higher effective concentration of free H⁺ ions for acid reactions. | Lower effective concentration of free H⁺ ions due to less water for dissociation. |
| Viscosity | Low, similar to water. | High, syrupy consistency. |
| Dehydrating Agent | Weak dehydrating properties. | Extremely powerful dehydrating agent. |
| Oxidizing Agent | Weak oxidizing properties. | Strong oxidizing agent, especially when hot. |
| Primary Use | Acidic reactions, electrolyte in batteries, industrial processes. | Dehydrating agent, catalyst, strong oxidizer, raw material for other chemicals. |
| Safety | Corrosive, causes chemical burns. Handle with care. | Extremely corrosive, causes severe burns, strong dehydrator. Handle with extreme care. |
For a deeper understanding of acid strength, refer to resources like Khan Academy on Acids and Bases or LibreTexts Chemistry.
Practical Applications
Dilute sulphuric acid plays a crucial role in various applications:
- Car Batteries (Lead-Acid Batteries): A 30-50% dilute solution of sulphuric acid acts as the electrolyte. Its strong acidic nature facilitates the electrochemical reactions necessary for battery operation.
- Fertilizer Production: It is used in the production of superphosphate fertilizers.
- Industrial Cleaning: Employed in pickling processes to remove rust and impurities from metals before plating or coating.
- Chemical Synthesis: A reagent in many organic and inorganic reactions.
In conclusion, regardless of its dilution, sulphuric acid maintains its classification as a strong acid because of its fundamental ability to ionize extensively in water. Dilution simply modifies the concentration of the acid and, by providing more water, allows for a greater effective number of free hydrogen ions to be present, making its acidic reactions more prominent than in concentrated forms where other properties dominate.
