The halogens

Question 1

How do the halogens occur in nature?

Answer 1

not in their elemental form
occur as stable halide ions dissolved in sea water or in solid deposits

Question 2

What does flourine look like?

Answer 2

very pale yellow gas

Question 3

What does chlorine look like?

Answer 3

greenish, reactive gas, poisonous in high conc

Question 4

What does bromine look like?

Answer 4

red liquid that gives off dense bronw/orange poisonous fumes

Question 5

What does iodine look like?

Answer 5

shiny grey solid that sublimes (changes) to purple gas

Question 6

How do the states of the halogens change down the group?

Answer 6

gas –> liquid –> solid down the group

Question 7

Why does MP and BP increase down the group?

Answer 7

there are more electrons
so stronger london forces
so more energy required

Question 8

What is reduced in a redox reaction with halogens?

Answer 8

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

Question 9

What do halide-halogen displacement reactions show?

Answer 9

reactivity decreases down the group

Question 10

What happens during a halide-halogen displacement reaction?

Answer 10

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

Question 11

What happens when chloride ions are added to each halogen?

Answer 11

no reactions take place as chlorine is the most reactive
chlorine - very pale green solution
bromine - yellow solution
iodine - brown solution

Question 12

What happens when bromide ions are added to each halogen?

Answer 12

chlorine = pale -yellow solution —> orange solution - cl displaced Br
no reaction with bromine and iodine

Question 13

What happens when iodide ions are added to each halogen?

Answer 13

chlorine - pale yellow solution —> brown solution = cl displaced I
bromine = orange —> brown = br displaced I
iodine - no reaction

Question 14

What is added to tell solutions of bromine and iodine apart and why not water?

Answer 14

cyclohexane is added - non-polar halogens dissolve more readilty in cylcohexane than water

Question 15

What colour is chlorine solution with cyclohexane added?

Answer 15

colourless top layer

Question 16

What colour is bromine solution with cyclohexane added?

Answer 16

orange top layer

Question 17

what colour is iodine solution with cyclohexane added?

Answer 17

violet top layer

Question 18

Why is chlorine more reactive than bromine (the other halogens)?

Answer 18

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

Question 19

Why does reactivity decrease down the group?

Answer 19

atomic radius increases
so more inner shells so more sheilding
less nuclear attraction go capture an electron from another species
reactivity decreases

Question 20

What is disproportionation?

Answer 20

a redox reaction in which the same element is both oxidised and reduced

Question 21

What is an example of a disproportionation reaction with chlorine and water?

Answer 21

Cl2 + H2O –> HClO + HCl
the chlorine in HClO is oxidised - 0–> +1
the chlorine in HCl is reduced = 0 —> -1

Question 22

What is chloric acid?

Answer 22

acts as a weak bleach

Question 23

What is an example of a disproportionation reaction with chlorine and sodium hydroxide?

Answer 23

Cl2 + 2NaOH —> NaClO + NaCl + H2O
the cl in NaClO is oxidised = 0 –> +1
the cl in NaCl is reduced = 0 –> -1

Question 24

What is NaClO?

Answer 24

sodium chlorate - household bleach

Question 25

What would happen if you added universal indicator to the disproportionation reaction wirth chlorine and water?

Answer 25

it will turn red initially due to x2 acids being produced, then it will turn colourless ad HClO bleaches the colour

Question 26

What is the good thing about chlorine?

Answer 26

it kills bacteria - used in swimming pools and drinking water

Question 27

What are the issues with chlorine?

Answer 27

it is toxic in high conc - it is a resp irritant
chlorinated hydrocarbons could form and they are suspected of causing cancers

Question 28

What test is carried out to detect halide ions?

Answer 28

precipitation reactions with aqueous silver ions
forms precipitates of silver halides
Ag+ + X- —> AgX

Question 29

Why is nitric acid added to the silver halide reaction?

Answer 29

the nitric acid reacts with any carbonates present to prevent the formation of the precipitate Ag2CO3

Question 30

What colour precipitates are formed in the halide and silver nitrate reactions?

Answer 30

chloride = white precipitate
bromide = cream precipitate
iodide = yellow precipitate

Question 31

What can the silver haldie precipitates be treated with if they look too similar?

Answer 31

ammonia solution

Question 32

What is the equation of the reaction of silver chloride and ammonia?

Answer 32

AgCl (s) + 2NH3 (aq) –> [Ag(NH3)2]+ (aq) + cl- (aq)

Question 33

What is the reaction of silver bromide and ammonia?

Answer 33

AgBr (s) + 2NH3 (aq) –> [Ag(NH3)2]+ (aq) + Br- (aq)

Question 34

Why doesnt silver iodide react with ammonia?

Answer 34

silver iodide is too insoluble