8.2 the halogens module 3 Flashcards
what are the physical properties of the halogens?
most reactive non-metallic group
elements do not occur in their elemental form in nature
halogens occur as stable halide ions dissolved in seawater
colour and state of fluorine
pale yellow gas
toxic
colour and state of chlorine
pale green gas
toxic
colour and state of bromine
red-brown liquid
very volatile
colour and state of iodine
shiny grey-black solid
colour and state of astatine
never been seen
radioactive
what is the trend in bps in the halogens?
bp increases down the group
more electrons
stronger London forces
more energy required to break the intermolecular forces
boiling point increases
what is trend in reactivity in the halogens?
less reactive down the group
atomic radius increases
less nuclear attraction
more shielding
harder to attract electrons
what is the most common reactions within halogens?
redox reaction
what happens within a redox reaction of a halogen?
each halogen atom is reduced
halogen is an oxidising agent
what happens during a halogen-halide displacement reaction?
halogen displaces halide form the compound
if the solution changes colour, displacement reaction has happened
what are the colours of chlorine, bromine and iodine in the water?
pale green
orange
brown
how do we make it more clear that a displacement reaction has occurred?
add cyclohexane
what are the colours of chlorine, bromine and iodine in cyclohexane?
pale green
orange
violet
define disproportionation
a redox reaction where the same element is both oxidised and reduced
what happens when small amounts of chlorine is added to water?
a disproportionation reaction occurs
what are the products of a reaction between chlorine and water?
chloric acid (I) HClO
hydrochloric acid HCl
what is the chlorine and water reaction used for?
used in water purification
bacteria is killed by the chloric (I) acid
what does the reaction of chlorine with cold, aqueous, dilute sodium hydroxide form?
sodium chlorate NaClO
sodium chloride NaCl
what are the risks of chlorine use?
it is a respiratory irritant
can react with organic hydrocarbons to form chlorinated hydrocarbons that are suspected of causing cancer
however, overall risk of not adding chlorine to water supply is far greater than any of the risks
what are the tests for halide ions?
aqueous halide ions react with aqueous silver ions to form precipitates of silver halides
Ag+ + X- —-> AgX (s)
