Non-metals and their oxides, and uses of non-metals
Non-metals burn in oxygen to give oxides that are usually acidic; a few, like CO, are neutral. Metal oxides are basic. Both kinds of element have many uses.
Non-metals burning in oxygen
| Non-metal | Balanced equation | Oxide formed |
|---|---|---|
| Sulphur | S(s) + O₂(g) → SO₂(g) | Sulphur dioxide (acidic) |
| Carbon, in plenty of air | C(s) + O₂(g) → CO₂(g) | Carbon dioxide (acidic) |
| Carbon, in limited air | 2C(s) + O₂(g) → 2CO(g) | Carbon monoxide (neutral) |
| Hydrogen | 2H₂(g) + O₂(g) → 2H₂O(l) | Water (neutral) |
Four kinds of oxide
| Kind | Examples | Reacts with |
|---|---|---|
| Basic | Na₂O, K₂O, CaO, MgO (metal oxides) | Acids; those that dissolve in water give bases |
| Acidic | CO₂, SO₂, SO₃, NO₂, N₂O₅ (non-metal oxides) | Bases; they give acids with water |
| Amphoteric | Al₂O₃, ZnO | Both acids and bases |
| Neutral | CO, N₂O, NO, H₂O | Neither acids nor bases |
Acidic oxides with water and with bases
| Reaction | Balanced equation |
|---|---|
| Carbon dioxide + water | CO₂(g) + H₂O(l) → H₂CO₃(aq), carbonic acid |
| Sulphur trioxide + water | SO₃(g) + H₂O(l) → H₂SO₄(aq), sulphuric acid |
| Dinitrogen pentoxide + water | N₂O₅(g) + H₂O(l) → 2HNO₃(aq), nitric acid |
| Sulphur dioxide + sodium hydroxide | SO₂ + 2NaOH → Na₂SO₃ + H₂O |
| Carbon dioxide + sodium hydroxide | CO₂ + 2NaOH → Na₂CO₃ + H₂O |
Oxides of nitrogen
| Name | Formula | Nature |
|---|---|---|
| Nitrous oxide (laughing gas) | N₂O | Neutral |
| Nitric oxide | NO | Neutral |
| Dinitrogen trioxide | N₂O₃ | Acidic |
| Nitrogen dioxide | NO₂ | Acidic |
| Dinitrogen tetroxide | N₂O₄ | Acidic |
| Dinitrogen pentoxide | N₂O₅ | Acidic |
Activity: metal oxides are basic, non-metal oxides acidic (online lab or teacher demonstration)
- 1Hold a short magnesium ribbon with tongs in a flame and collect the white ash.Magnesium oxide, MgO, forms
- 2★Dissolve the ash in a little warm water and test with red and blue litmus.Red litmus turns blue: the solution, Mg(OH)₂, is basic
- 3(Teacher only) Burn a little sulphur in a deflagrating spoon inside a gas jar, then shake the gas with a little water.Do this in open air or a fume cupboard, as SO₂ is harmful
- 4★Test this solution with blue litmus.Blue litmus turns red: the solution is acidic
★ key step
Uses of non-metals
| Non-metal | Uses |
|---|---|
| Hydrogen | Making ammonia, and from it urea fertiliser; fuels such as water gas (CO + H₂) and coal gas (H₂ + CH₄) |
| Silicon | Transistors, computer chips and solar (photovoltaic) cells; removing oxygen from steel to make high-quality steel |
| Phosphorus | Phosphoric acid, H₃PO₄, for phosphate fertilisers; phosphorus compounds (such as P₄S₃) in matches; phosphates in detergents |
| Sulphur | Controlling fungus and pests on farms; gunpowder (sulphur, charcoal and potassium nitrate); making sulphuric acid, the king of chemicals |
| Chlorine and other halogens | Form salts (halides) such as NaCl, KBr and KI; sea water is their main source |
Urea, the fertiliser most Indian farmers use, is made from ammonia, which needs hydrogen. The solar panels on rooftops and the chip in your mobile phone are made of silicon, a non-metal.
2 marks: “Classify these oxides as acidic, basic, amphoteric or neutral: SO₂, MgO, ZnO, CO.” SO₂: acidic. MgO: basic. ZnO: amphoteric. CO: neutral.
3 marks: “An element burns in air, and its oxide dissolves in water to give a solution that turns blue litmus red. (i) Is the element a metal or a non-metal? (ii) Give an example, with equations for burning and for dissolving. (iii) Name a neutral oxide of a non-metal.” (i) A non-metal, because its oxide is acidic. (ii) Carbon: C + O₂ → CO₂; CO₂ + H₂O → H₂CO₃. (iii) Carbon monoxide, CO (or N₂O).
2 marks: “Give two uses each of sulphur and silicon.” Sulphur: controlling fungus and pests; making sulphuric acid (or gunpowder). Silicon: computer chips and transistors; solar cells (or making steel).
Non-metal oxide + water = acid; metal oxide + water = base. CO and N₂O sit on the fence (neutral).