Oxidising and displacement properties
Oxidation is the loss of electrons and reduction is the gain of electrons. An oxidising agent takes electrons from another substance. The halogens are oxidising agents. Their strength decreases down the group: fluorine > chlorine > bromine > iodine. A more reactive halogen displaces a less reactive halogen from a solution of its halide.
| Reaction | Observation | Equation |
|---|---|---|
| Chlorine water + potassium bromide solution | The solution turns orange (bromine) | Cl₂ + 2KBr → 2KCl + Br₂ |
| Chlorine water + potassium iodide solution | The solution turns brown (iodine) | Cl₂ + 2KI → 2KCl + I₂ |
| Bromine water + potassium iodide solution | The solution turns brown | Br₂ + 2KI → 2KBr + I₂ |
| Iodine + potassium chloride solution | No reaction | Iodine is less reactive than chlorine |
| Reducing and oxidising agents | Change seen |
|---|---|
| Acidified potassium manganate(VII) + a reducing agent (e.g. SO₂, Fe²⁺) | Purple solution becomes colourless |
| Acidified potassium dichromate(VI) + a reducing agent | Orange solution becomes green |
| Chlorine (oxidising agent) bleaches damp litmus paper | Litmus turns white |
Preparation of sulphuric acid
Sulphuric acid is the most important industrial chemical. It is made by the contact process from sulphur (or from sulphide ores such as zinc blende). It is used to make fertilisers, detergents, paints, plastics, and for car batteries.
Try itSulphuric acid from sulphur
Choose the mass of sulphur burnt and the percentage yield of the whole process. Each mole of sulphur can give one mole of sulphuric acid. (S = 32, H₂SO₄ = 98)
Properties and uses
| Substance | Important uses |
|---|---|
| Sulphuric acid | Fertilisers (ammonium sulphate), detergents, paints, car batteries, refining metals |
| Chlorine | Water treatment, bleach, plastics (PVC) |
| Ammonia | Fertilisers, explosives, cleaning fluids |
| Nitric acid | Fertilisers (ammonium nitrate), explosives |
| Hydrogen chloride | Hydrochloric acid for cleaning metals |
Key terms
- Oxidising agent
- A substance that takes electrons from another substance.
- Displacement
- A more reactive element replacing a less reactive element in a compound.
- Contact process
- The industrial method for making sulphuric acid.
- Oleum
- Sulphur trioxide dissolved in concentrated sulphuric acid.
Summary
- Halogens are oxidising agents; reactivity decreases from fluorine to iodine.
- A more reactive halogen displaces a less reactive one from its halide.
- Contact process: S → SO₂ → SO₃ (V₂O₅, 450 °C) → oleum → H₂SO₄.
- Sulphuric acid is used in fertilisers, detergents, paints and batteries.