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Reactions of the halogens
Halogens react with metals such as sodium and iron:
They also take part in displacement reactions with halide ions, such as the reaction that is used to make bromine from potassium bromide in seawater:
halogen + hydrogen hydrogen halide
They also react with non-metals such as hydrogen:
halogen + sodium sodium halide
chlorine +potassiumbromide
potassiumchloride
bromine +
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Reaction with iron
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Reactions with hydrogen
Chlorine and hydrogen explode in bright sunlight but react slowly in the dark.
The halogens react with hydrogen gas to product hydrogen halides. For example:
Cl2(g) + H2(g) 2HCl(g)
Iodine combines partially and very slowly with hydrogen, even on heating.
Bromine and hydrogen react slowly on heating with a platinum catalyst.
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Redox reactions of halogens
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What is the reactivity of the halogens?
The reactions of the halogens with iron and hydrogen show that their reactivity decreases down the group.
How do you think fluorine and astatine would react with iron wool and hydrogen?
Iron wool burns and glows brightly.
Iron wool has a very slight glow.
Iron wool glows but less brightly than with chlorine.
chlorine
bromine
iodine
Halogen Reaction with iron wool
Reaction with hydrogen
Explodes in sunlight, reacts slowly in the dark.
Reacts slowly on heating with catalyst.
Reacts partially and very slowly.
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Electron structure and reactivity
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Halogen displacement reactions
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Halogen displacement reactions
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Halogen displacement reactions
Halogen displacement reactions are redox reactions.
Cl2 + 2KBr 2KCl + Br2
To look at the transfer of electrons in this reaction, the following two half equations can be written:
Chlorine has gained electrons, so it is reduced to Cl- ions.
What has been oxidized and what has been reduced?
2Br- Br2 + 2e-Cl2 + 2e- 2Cl-
Bromide ions have lost electrons, so they have been oxidized to bromine.
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Oxidizing ability of halogens
fluorine
incr
easi
ng
oxi
diz
ing
ab
ility
iodine
bromine
chlorine
In displacement reactions between halogens and halides, the halogen acts as an oxidizing agent.
This means that the halogen:
What is the order of oxidizing ability of the halogens?
is reduced to form the halide ion.
gains electrons
oxidizes the halide ion to the halogen
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Oxidizing ability of halogens
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Chlorine and disproportionation
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Reaction of chlorine with water
Chlorination of drinking water raises questions about individual freedom because it makes it difficult for individuals to opt out.
Chlorine is used to purify water supplies because it is toxic to bacteria, some of which can cause disease. Adding it to water supplies is therefore beneficial for the population.
However, chlorine is also toxic to humans, so there are risks associated with gas leaks during the chlorination process. There is also a risk of the formation of chlorinated hydrocarbons, which are also toxic.
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Bleach and the chlorate(I) ion
Household bleach commonly contains the chlorate(I) ion, ClO-, in the form of sodium chlorate(I), NaOCl.
ClO- + H2O + Cl- + 2OH-
The chlorine has been reduced because it has gained electrons. Its oxidation state has decreased from +1 in ClO- to –1 in Cl-.
How many electrons are needed to balance this equation?
The chlorate(I) ion behaves as an oxidizing agent. It oxidizes the organic compounds in food stains, bacteria and dyes.
Has the chlorine been oxidized or reduced in the reaction?
2e-
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Redox reactions of chlorate ions