Each halogen atom is reduced (it is an oxidising agent), gaining one electron to form a 1- halide ion.
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What is the trend in reactivity down the group, and how is this tested?
Reactivity decreases down the group; a solution of each halogen is added to aqueous solutions of the other halides; if the halogen added is more reactive than the halide, then a reaction and colour change will occur.
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What are the colour of Chlorine, Bromine and Iodine in water and cyclohexane?
Chlorine - pale green in both; Bromine - orange in both; Iodine - brown in water and violet in cyclohexane.
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Explain the trend in reactivity.
Down the group - atomic radius increases, shielding increases, less nuclear attraction, reactivity decreases.
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What does disproportionation mean?
A redox reaction in which the same element is both oxidised and reduced.
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How is chlorine used in water treatment?
When chlorine is added to water, a disproportionation reaction occurs; the two products are both acids, chloric (I) acid, HClO, and hydrochloric acid, HCl; the bacteria is killed by the chloric (I) acid, which also acts as a bleach.
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How does chlorine form bleach?
Chlorine will dissolve in water if aqueous sodium hydroxide is present, the resulting solution contains a large concentration of chlorate (I), ClO - ions from the sodium chlorate (I), NaClO, that is formed.
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What are the benefits of chlorine use compared with the risks?
Benefit - kills bacteria and water-bourne diseases; Risks - hazards of toxic chlorine gas, risk of cancer from chlorinated hydrocarbons.
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How can you test for halide ions?
Aqueous halide ions react with aqueous silver ions to form precipitates of silver halides; Ag+ + X- = AgX; aqueous ammonia is then added to test the solubility of the precipitate, Cl- is soluble in dil NH3, Br- is soluble in conc NH3, I- insoluble.
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