Bromine is extracted from seawater. Seawater contains 0.065 g of bromide ions, Br−\mathrm{Br^{-}}Br−, in each dm3\mathrm{dm^{3}}dm3. Chlorine gas is bubbled through the seawater:
Cl2(g)+2Br−(aq)→2Cl−(aq)+Br2(aq)\mathrm{Cl_{2}(g)} + \mathrm{2Br^{-}(aq)} \rightarrow \mathrm{2Cl^{-}(aq)} + \mathrm{Br_{2}(aq)}Cl2(g)+2Br−(aq)→2Cl−(aq)+Br2(aq)
Write the half equation for the conversion of bromide ions into bromine.
In a later stage, the bromine is reacted with sulfur dioxide and water: Br2+SO2+2H2O→2HBr+H2SO4\mathrm{Br_{2}} + \mathrm{SO_{2}} + \mathrm{2H_{2}O} \rightarrow \mathrm{2HBr} + \mathrm{H_{2}SO_{4}}Br2+SO2+2H2O→2HBr+H2SO4
In solution, HBr is present as H+\mathrm{H^{+}}H+ ions and Br−\mathrm{Br^{-}}Br− ions. State whether bromine is oxidised or reduced in this stage. Explain your answer in terms of electrons.
Calculate the volume of chlorine gas, at room temperature and pressure, needed to react with all the bromide ions in 1000 dm3\mathrm{dm^{3}}dm3 of seawater.
Relative atomic mass: Br = 80. One mole of any gas occupies 24 dm3\mathrm{dm^{3}}dm3 at room temperature and pressure.
Explain, in terms of electronic configuration, why chlorine can be used to extract bromine from seawater but iodine cannot.
41 exam-style questions on Edexcel GCSE Chemistry 7.2 Group 7, covering 7.2.1 Physical properties of the halogens, 7.2.2 Reactions of the halogens, 7.2.3 Relative reactivity and displacement reactions of the halogens, and 7.2.4 Halogen displacement as a redox reaction. Each one has a worked solution and a mark scheme showing where the marks go.