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Why halogens weaken as oxidisers down the group

Science · Chemistry · ages 16-17

Name ______________________ Date ____________

You add chlorine water to a bromide solution. What happens?
- Bromine forms and colour changes
- No reaction occurs in this mixture
- Chloride is displaced by bromine
Why does oxidising power fall down Group 7?
- The nucleus loses protons down the group
- Atoms grow, and inner shells shield the pull
- The outer shell moves closer to the nucleus
A white precipitate forms with silver nitrate and dissolves in dilute ammonia. Which halide is present?
- Chloride
- Bromide
- Iodide
What are the main redox products when concentrated sulfuric acid reacts with sodium bromide?
- HBr gas only
- Br2, SO2 and water
- Br2, H2S, S and water
When chlorine displaces bromine, what is oxidised and what is reduced?
- Chlorine loses electrons; bromide gains
- Bromide loses electrons; chlorine gains
- Both species gain electrons
Yellow silver iodide dissolves in concentrated ammonia.
Circle one: True False
A student predicts bromine will displace chlorine from chloride solution. What explains the result?
- Bromine is weaker, so no displacement
- Chlorine is weaker than bromine here
- A chloride solution always frees a halogen
Concentrated sulfuric acid gives hydrogen chloride with sodium chloride, but iodine, sulfur dioxide, hydrogen sulfide and sulfur with sodium iodide. Why?
- Iodide is easiest to oxidise and reduces the acid further
- Chloride is easier to oxidise than iodide in this test
- No halide can reduce concentrated sulfuric acid

Answer key

For grown-ups. Fold this page away before handing over the rest.

Bromine forms and colour changes · Chlorine is the stronger oxidising agent. It gains electrons from bromide ions, which become bromine.
Atoms grow, and inner shells shield the pull · A new electron joins a shell farther from a more shielded nucleus, so the attraction becomes weaker.
Chloride · White silver chloride dissolves in dilute ammonia. Cream silver bromide needs concentrated ammonia, while yellow silver iodide remains.
Br2, SO2 and water · Bromide is oxidised to bromine and the acid is reduced mainly to sulfur dioxide. Hydrogen bromide forms first, but the reaction goes further, and only iodide is strong enough to reduce the acid on to hydrogen sulfide and sulfur.
Bromide loses electrons; chlorine gains · Bromide loses electrons to form bromine, so it is oxidised. Chlorine gains those electrons to form chloride, so it is reduced.
False · Silver iodide is yellow and remains undissolved even in concentrated ammonia.
Bromine is weaker, so no displacement · Chlorine is the stronger oxidising agent. Bromine cannot take electrons from chloride, so no displacement occurs.
Iodide is easiest to oxidise and reduces the acid further · Iodide gives up electrons more easily than chloride. It is oxidised to iodine and reduces the acid to sulfur dioxide, hydrogen sulfide and sulfur. Chloride does not reduce the acid, so only hydrogen chloride forms.