Why these three compounds matter
Ever wondered why a single lab bottle can change the colour of a flame or why factories talk about "acid rain"? That bottle often holds ammonia, nitric acid or sulphuric acid – three chemicals that shape everything from fertilizers to explosives.
💡 In Simple Words: Ammonia is a light‑smelling gas that plants love, nitric acid is a strong, colourless liquid that can turn metals into nitrates, and sulphuric acid is a thick, oily liquid that can soak up water like a sponge. All three are key players in everyday chemistry and in your ICSE exam.
Ammonia (NH3)
What is it?
Ammonia is a colourless gas with a sharp, pungent smell. Its formula NH3 tells you it has one nitrogen atom bonded to three hydrogen atoms. Think of it as a tiny tripod where nitrogen sits at the centre and the three hydrogens are the legs.
Key properties
- Physical state: gas at room temperature; liquefies under pressure.
- Solubility: dissolves well in water, forming a basic (alkaline) solution called ammonium hydroxide.
- pH: around 11, which means it can neutralise acids.
- Odour: strong, similar to cleaning products.
How is it prepared in the lab?
The classic method is the dry distillation of ammonium chloride and quicklime (calcium oxide). When heated, ammonium chloride breaks down and reacts with calcium oxide, releasing ammonia gas:
NH4Cl + CaO → NH3↑ + CaCl2
In industry, the Haber‑Bosch process combines nitrogen from air with hydrogen (usually from natural gas) under high pressure and temperature, using an iron catalyst.
Important uses
- Fertiliser: reacts with acids to give ammonium nitrate, a common nitrogen source for crops.
- Cleaning agent: its alkaline solution cuts grease.
- Refrigerant: because it evaporates quickly, pulling heat away.
Nitric Acid (HNO3)
What is it?
Nitric acid is a colourless, highly corrosive liquid that smells like sharp vinegar. Its formula HNO3 means one hydrogen, one nitrogen and three oxygens. Imagine a tiny tower where nitrogen sits on a base of three oxygen atoms, with a hydrogen hanging off the side.
Key properties
- Physical state: liquid; can be concentrated (about 68%) or dilute.
- Reactivity: strong oxidising agent – it can pull electrons away from other substances, causing them to burn.
- Acidity: pH around 1, so it’s very acidic.
- Fuming: when concentrated, it releases nitrogen dioxide (brown gas) – that’s the “fuming” you see.
Lab preparation
One simple way is the reaction of sodium nitrate with sulfuric acid:
NaNO3 + H2SO4 → HNO3 + NaHSO4
Heat drives off the nitric acid vapour, which is then condensed.
Major uses
- Manufacturing fertilizers like ammonium nitrate and calcium nitrate.
- Making explosives (e.g., TNT) where the nitrate ion provides oxygen for rapid combustion.
- Etching and cleaning metals because it dissolves many metals without leaving residues.
Sulphuric Acid (H2SO4)
What is it?
Sulphuric acid is a dense, oily liquid that looks like water but feels sticky. Its formula H2SO4 tells you there are two hydrogens, one sulphur, and four oxygens. Think of the sulphur atom as a central hub with four oxygen spokes and two hydrogens hanging off like tiny balloons.
Key properties
- Physical state: liquid; very viscous (thick).
- Acidity: extremely strong, pH close to 0.
- Dehydrating power: it can pull water out of other substances – it’s like a chemical sponge.
- Oxidising ability: can oxidise metals, but not as aggressively as nitric acid.
Industrial preparation (Contact Process)
The most common method is the Contact Process, which involves three main steps. Below is a simple flowchart that shows the sequence.
First, sulphur is burnt in air to give sulphur dioxide (SO2). A catalyst (usually V2O5) helps convert SO2 to sulphur trioxide (SO3). Finally, SO3 is dissolved in water to produce the acid.
Important uses
- Battery acid in lead‑acid batteries that power cars and UPS systems.
- Manufacturing fertilizers such as super‑phosphate.
- Cleaning agents and metal pickling – it removes rust by reacting with iron oxide.
- Petroleum refining – helps break large hydrocarbon molecules into gasoline.
Quick comparison
| Aspect | Ammonia (NH3) | Nitric Acid (HNO3) | Sulphuric Acid (H2SO4) |
|---|---|---|---|
| State at RT | Gas | Liquid | Liquid (viscous) |
| pH (1 M) | ~11 (basic) | ~1 (strong acid) | ~0 (very strong acid) |
| Key property | Weak base, good fertilizer source | Strong oxidiser, makes nitrates | Powerful dehydrator & acid |
| Major industrial use | Ammonium nitrate fertilizer | Explosives & nitrates | Battery acid & phosphates |
| Safety note | Inhalation irritant | Corrosive, toxic fumes | Highly corrosive, burns skin |
📝 Likely Exam Questions
- Write the balanced chemical equation for the laboratory preparation of ammonia. Answer: NH4Cl + CaO → NH3↑ + CaCl2
- Explain why nitric acid is called a strong oxidising agent. Answer: It can accept electrons from many metals and non‑metals, converting them to their nitrate salts while the nitrogen in HNO3 is reduced to nitrogen oxides.
- List two important uses of sulphuric acid in industry and give a short reason for each. Answer: (i) Battery acid – provides the electrolyte that conducts ions in lead‑acid batteries. (ii) Manufacture of super‑phosphate fertilizer – reacts with calcium carbonate to release phosphate ions for plant nutrition.
- Compare the physical states and acidity of the three compounds. Answer: Ammonia is a gas and weakly basic (pH ~11). Nitric acid is a colourless liquid, strong acid (pH ~1). Sulphuric acid is a viscous liquid, very strong acid (pH ~0).
- Describe one safety precaution when handling each of the three chemicals. Answer: Ammonia – work in a well‑ventilated area or use a fume hood. Nitric acid – wear goggles and a face shield to avoid corrosive fumes. Sulphuric acid – use acid‑resistant gloves and add acid to water, never the reverse.