The halogens Flashcards
How do the halogens occur in nature?
not in their elemental form
occur as stable halide ions dissolved in sea water or in solid deposits
What does flourine look like?
very pale yellow gas
What does chlorine look like?
greenish, reactive gas, poisonous in high conc
What does bromine look like?
red liquid that gives off dense bronw/orange poisonous fumes
What does iodine look like?
shiny grey solid that sublimes (changes) to purple gas
How do the states of the halogens change down the group?
gas –> liquid –> solid down the group
Why does MP and BP increase down the group?
there are more electrons
so stronger london forces
so more energy required
What is reduced in a redox reaction with halogens?
each halogen atom is reduced - gains an electron to form a halide ion
another species loses electrons to halogen atoms so the halogen is the oxidising agent
What do halide-halogen displacement reactions show?
reactivity decreases down the group
What happens during a halide-halogen displacement reaction?
a solution of each halogen is added to aqueous solutions of other halides
if the halogen added is more reactive that the halide:
a reaction takes place, displacing the halide from solution and the solution changes colour
What happens when chloride ions are added to each halogen?
no reactions take place as chlorine is the most reactive
chlorine - very pale green solution
bromine - yellow solution
iodine - brown solution
What happens when bromide ions are added to each halogen?
chlorine = pale -yellow solution —> orange solution - cl displaced Br
no reaction with bromine and iodine
What happens when iodide ions are added to each halogen?
chlorine - pale yellow solution —> brown solution = cl displaced I
bromine = orange —> brown = br displaced I
iodine - no reaction
What is added to tell solutions of bromine and iodine apart and why not water?
cyclohexane is added - non-polar halogens dissolve more readilty in cylcohexane than water
What colour is chlorine solution with cyclohexane added?
colourless top layer
What colour is bromine solution with cyclohexane added?
orange top layer
what colour is iodine solution with cyclohexane added?
violet top layer
Why is chlorine more reactive than bromine (the other halogens)?
chlorine will gain an electron and form a negative ion more easily than bromine because chlorine is smaller so chlorine’s electrons are less sheilded so the electron to be gained is more attracted in chlorine
Why does reactivity decrease down the group?
atomic radius increases
so more inner shells so more sheilding
less nuclear attraction go capture an electron from another species
reactivity decreases
What is disproportionation?
a redox reaction in which the same element is both oxidised and reduced
What is an example of a disproportionation reaction with chlorine and water?
Cl2 + H2O –> HClO + HCl
the chlorine in HClO is oxidised - 0–> +1
the chlorine in HCl is reduced = 0 —> -1
What is chloric acid?
acts as a weak bleach
What is an example of a disproportionation reaction with chlorine and sodium hydroxide?
Cl2 + 2NaOH —> NaClO + NaCl + H2O
the cl in NaClO is oxidised = 0 –> +1
the cl in NaCl is reduced = 0 –> -1
What is NaClO?
sodium chlorate - household bleach
What would happen if you added universal indicator to the disproportionation reaction wirth chlorine and water?
it will turn red initially due to x2 acids being produced, then it will turn colourless ad HClO bleaches the colour
What is the good thing about chlorine?
it kills bacteria - used in swimming pools and drinking water
What are the issues with chlorine?
it is toxic in high conc - it is a resp irritant
chlorinated hydrocarbons could form and they are suspected of causing cancers
What test is carried out to detect halide ions?
precipitation reactions with aqueous silver ions
forms precipitates of silver halides
Ag+ + X- —> AgX
Why is nitric acid added to the silver halide reaction?
the nitric acid reacts with any carbonates present to prevent the formation of the precipitate Ag2CO3
What colour precipitates are formed in the halide and silver nitrate reactions?
chloride = white precipitate
bromide = cream precipitate
iodide = yellow precipitate
What can the silver haldie precipitates be treated with if they look too similar?
ammonia solution
What is the equation of the reaction of silver chloride and ammonia?
AgCl (s) + 2NH3 (aq) –> [Ag(NH3)2]+ (aq) + cl- (aq)
What is the reaction of silver bromide and ammonia?
AgBr (s) + 2NH3 (aq) –> [Ag(NH3)2]+ (aq) + Br- (aq)
Why doesnt silver iodide react with ammonia?
silver iodide is too insoluble
