Fluorine, chlorine, bromine and iodine are all halogens in Group 7 of the periodic table. A student dissolves chlorine gas in water to produce chlorine water. The chlorine water is described as a good oxidising agent. Explain, in terms of electron transfer, why chlorine acts as an oxidising agent, and state what happens to the chlorine atoms as a result.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Halogens are found in Group 7 of the periodic table. They gain an electron to form halide ions with a 1− charge. An oxidising agent is a species which brings about oxidation by gaining electrons and is itself reduced.
Model answer (4 marks)
Chlorine atoms in chlorine water accept electrons from the species they oxidise.
1. The chlorine atoms gain electrons.
2. By gaining electrons they are reduced to chloride ions (Cl⁻).
3. The species that donates the electrons loses electrons and is oxidised.
4. Because chlorine is the species that is reduced, it functions as the oxidising agent.
1. The chlorine atoms gain electrons.
2. By gaining electrons they are reduced to chloride ions (Cl⁻).
3. The species that donates the electrons loses electrons and is oxidised.
4. Because chlorine is the species that is reduced, it functions as the oxidising agent.
Examiner tips
- Use the word ‘gain’ for reduction and ‘lose’ for oxidation. Mention that the chlorine atoms become Cl⁻. Show the electron transfer explicitly. Keep the answer short and to the points.
Common mistakes
- Saying that chlorine is oxidised instead of reduced. Forgetting to state that the other species is oxidised. Using vague terms like ‘reacts’ instead of ‘gains/loses electrons’.
Mark scheme (4 marks)
- Chlorine gains electrons (from another species)
- Chlorine is reduced / chlorine atoms become chloride ions (Cl⁻)
- The other substance / species loses electrons and is therefore oxidised
- An oxidising agent is itself reduced / chlorine acts as the oxidising agent because it is the species that gains the electrons
Key terms in this question
Related
- All Pearson Edexcel International GCSE Chemistry (4CH1) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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