Question: Chlorine water is added to aqueous potassium bromide. State what is observed, write an ionic equation and explain the result.Observation: the very pale green solution turns orange (yellow when dilute) because bromine is formed.Ionic equation: Cl2(aq) + 2Br-(aq) → 2Cl-(aq) + Br2(aq)Explanation: this is a displacement reaction. Chlorine is a stronger oxidising agent than bromine, so it removes electrons from bromide ions. Chlorine is reduced to chloride ions and bromide ions are oxidised to bromine.Oxidising ability decreases down group 7 because the atoms get larger and there is more shielding, so the attraction for an extra electron is weaker. This is why bromine cannot displace chloride ions.
Example Question - 1
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Specification: AQA Chemistry (7404), AS-level, 3.2.3.2 Uses of chlorine and chlorate(I). Topic: Group 7.
Key terms in this lesson
- displacement reaction
- A reaction in which a more reactive element displaces a less reactive element from a compound.
More in Group 7
- Sodium Bromide with Sulfuric Acid
- Sodium Iodide with Sulfuric Acid
- Reaction with Water
- Reaction with Alkali
- Example Question - 2
- Example Question - 3
- Silver Nitrate Test for Halide Ions
- Colours of Silver Halide Precipitates
All 20 lessons in Group 7 · All AQA AS-level Chemistry topics