Ever wondered why your garden fertilizer, fireworks, and car batteries all share a common chemical family?
Ammonia, nitric acid and sulphuric acid are three very important chemicals. They are used in everyday items from cleaning products to fertilizers, and they behave differently because of how many hydrogen atoms they can give away.
What is Ammonia?
Ammonia (chemical formula NH₃) is a colour‑less gas with a pungent smell, like the scent of strong cleaning liquid. In simple terms, think of it as a tiny ball made of one nitrogen atom holding hands with three hydrogen atoms.
Key properties
- Weak base – it can accept a hydrogen ion (H⁺) from acids.
- Very soluble in water; forms a solution called ammonium hydroxide.
- Boils at –33°C, so it turns into a gas at room temperature.
Common uses
- Fertiliser – provides nitrogen for plant growth.
- Cleaning agent – dissolves grease and stains.
- Refrigerant – used in large‑scale cooling systems.
What is Nitric Acid?
Nitric acid (HNO₃) is a colourless, highly corrosive liquid that releases brown nitrogen dioxide fumes when it reacts with metals. Imagine it as a very aggressive cleaning spray that can eat away metal if you’re not careful.
Key properties
- Strong acid – readily donates its hydrogen ion.
- Oxidising agent – it can pull electrons away from other substances, causing them to rust or burn.
- Boils at 83°C and forms a pungent, toxic vapour.
Common uses
- Manufacturing of explosives like TNT.
- Making fertilizers (ammonium nitrate).
- Etching metals in jewellery and electronics.
What is Sulphuric Acid?
Sulphuric acid (H₂SO₄) is a thick, oily‑looking liquid that feels sticky to the touch. Think of it as the heavyweight champion of acids – it can squeeze water out of almost anything.
Key properties
- Strong acid – gives up two hydrogen ions.
- Dehydrating agent – removes water molecules from other compounds.
- Highly exothermic when diluted – releases a lot of heat.
Common uses
- Lead‑acid batteries in cars.
- Manufacturing of detergents, dyes, and pharmaceuticals.
- Processing of petroleum (refining).
How are they prepared industrially?
The three chemicals each have a famous large‑scale method. Below is a quick snapshot of each process.
Ammonia – Haber Process
Hydrogen (from natural gas) and nitrogen (from air) are squeezed together at high pressure (≈200 atm) and temperature (≈450 °C) with an iron catalyst. The reaction is:
N₂ + 3H₂ → 2NH₃
Nitric Acid – Ostwald Process
Ammonia from the Haber process is first oxidised to nitrogen monoxide (NO). That gas then reacts with more oxygen to form nitrogen dioxide (NO₂), which is finally absorbed in water to give nitric acid.
2NH₃ + 5O₂ → 4NO + 6H₂O 2NO + O₂ → 2NO₂ 3NO₂ + H₂O → 2HNO₃ + NO
Sulphuric Acid – Contact Process
Sulphur (or sulphur dioxide from burning sulphur) is first turned into sulphur trioxide (SO₃) using a vanadium(V) oxide catalyst, then SO₃ is dissolved in water (or more safely in concentrated H₂SO₄) to give the final acid.
S + O₂ → SO₂ 2SO₂ + O₂ → 2SO₃ (catalysed) SO₃ + H₂O → H₂SO₄
Comparison of the three acids
| Property | Ammonia (NH₃) | Nitric Acid (HNO₃) | Sulphuric Acid (H₂SO₄) |
|---|---|---|---|
| Type | Weak base | Strong acid (oxidising) | Strong acid (dehydrating) |
| Physical state | Gas at RT | Liquid, fumes | Viscous liquid |
| Key industrial process | Haber | Ostwald | Contact |
| Major use | Fertiliser | Explosives & fertilisers | Batteries & petrochemicals |
| Acid/base strength | pKb ≈ 4.75 (weak) | pKa ≈ –1.4 (very strong) | pKa₁ ≈ –3, pKa₂ ≈ 2 (very strong) |
📝 Likely Exam Questions
- Write the balanced chemical equation for the industrial preparation of ammonia. Answer: N₂ + 3H₂ → 2NH₃ (Haber process).
- Why is sulphuric acid called a dehydrating agent? Give an example. Answer: It removes water from substances; e.g., it converts sugar (C₆H₁₂O₆) into carbon and water: C₆H₁₂O₆ → 6C + 6H₂O.
- List two important uses of nitric acid in industry. Answer: Production of explosives (e.g., TNT) and manufacture of ammonium nitrate fertilizer.
- Compare the physical states of ammonia, nitric acid and sulphuric acid at room temperature. Answer: Ammonia is a colourless gas, nitric acid is a colourless liquid that gives off brown fumes, sulphuric acid is a thick, oily liquid.
- Explain how the Ostwald process links ammonia and nitric acid production. Answer: Ammonia produced in the Haber process is oxidised to NO, then to NO₂, and finally absorbed in water to form HNO₃, making the two processes consecutive industrial steps.