3.1.3 Halogens

Question 1

what do all halogens exist as

Answer 1

diatomic molecules

Question 2

fluorine

Answer 2

F2
very pale yellow gas
highly reactive

Question 3

chlorine

Answer 3

Cl2
greenish
reactive gas
poisonous in high concentrations

Question 4

bromine

Answer 4

Br2
red liquid
gives off dense brown/orange poisonous flames

Question 5

iodine

Answer 5

I2

shiny grey solid sublimes to purple gas

Question 6

trend in melting and boiling point down the group

Answer 6

increases
molecules are larger, more electrons so have more induced dipole-dipole forces
as forces get larger more energy must be put in to break them
increases MP and BP

Question 7

trend in reactivity down the group

Answer 7

decreases
atoms get bigger with more shielding, harder to attract and accept electrons
form 1- ions less easily down the group

Question 8

what will chlorine displace

Answer 8

bromide and iodide ions

Question 9

what will bromine displace

Answer 9

iodide ions

Question 10

chlorine in potassium chloride

Answer 10

very pale green solution

no reaction

Question 11

chlorine in potassium bromide

Answer 11

yellow solution

Cl has displaced Br

Question 12

chlorine in potassium iodide

Answer 12

brown solution

Cl has displaced I

Question 13

bromine in potassium chloride

Answer 13

yellow solution

no reaction

Question 14

bromine in potassium bromide

Answer 14

yellow solution

no reaction

Question 15

bromine in potassium iodide

Answer 15

brown solution

Br has displaced I

Question 16

iodine in potassium chloride

Answer 16

brown solution

no reaction

Question 17

iodine in potassium bromide

Answer 17

brown solution

no reaction

Question 18

iodine in potassium iodide

Answer 18

brown solution

no reaction

Question 19

colour of chlorine in solution

Answer 19

very pale green

often colourless

Question 20

colour of bromine in solution

Answer 20

yellow solution

Question 21

colour of iodine in solution

Answer 21

brown solution

Question 22

colour of chlorine in organic solvent

Answer 22

colourless

Question 23

colour of bromine in organic solvent

Answer 23

yellow

Question 24

colour of iodine in organic solvent

Answer 24

purple

Question 25

displacement reactions of chlorine if organic solvent is added

Answer 25

potassium chloride: colourless, no reaction
potassium bromide: yellow, Cl has displaced Br
potassium iodide: purple, Cl has displaced I

Question 26

displacement reactions of bromine if organic solvent is added

Answer 26

potassium chloride: yellow, no reaction
potassium bromide: yellow, no reaction
potassium iodide: purple, Br has displaced I

Question 27

displacement reactions of iodine if organic solvent is added

Answer 27

solution stays purple if potassium chloride, bromide or iodide is added as there is no reaction that occurs

Question 28

explain why chorine is more reactive than bromine

Answer 28

chlorine is more reactive than bromine
it will gain an electron and form an 1- ion more easily
because chlorine is smaller, has less shielding so the electron is attracted more strongly than in bromine

Question 29

example of a displacement reaction equation using chlorine and bromine

Answer 29

Cl2 (aq) + 2Br- (aq) -> 2Cl- (aq) + Br2 (aq)

Question 30

disproportionation reaction definition

Answer 30

a reaction where an element is both oxidised and reduced

Question 31

example of a disproportionation reaction: chlorine with water

Answer 31

chlorine with water
Cl2 (g) + H2O (l) -> HClO (aq) + HCl (aq)

if universal indicator was used it would initially turn red then HClO would bleach it colourless
chlorine both oxidised and reduced: 0 in Cl2 then -1 in HCl and +1 in HClO

Question 32

use of chlorine

Answer 32

in water to treat bacteria (drinking water and swimming pools)
benefits outweigh risk of toxic effects and risks from forming chlorinated hydrocarbons

Question 33

example of a disproportionation reaction: chlorine with sodium hydroxide

Answer 33

NaOH MUST BE COLD AND DILUTE
halogen will fade to colourless

Cl2(aq) + 2NaOH (aq) -> NaCl (aq) + NaClO (aq) + H2O (l)

Question 34

uses for the products of chlorine and sodium hydroxide disproportionation

Answer 34

NaCl and NaClO (sodium chorate I) is used as bleach and to disinfect bacteria

Question 35

what happens if the NaOH is hot

Answer 35

different disproportionation reaction will occur
3Cl2 + 6NaOH -> NaClO3 +5NaCl + 3H2O
forms sodium chlorate (V)

Question 36

testing for halides

Answer 36

add nitric acid

then add silver nitrate

Question 37

why do you need nitric acid when testing for halide ions

Answer 37

to react with any carbonates present to prevent formation of precipitate Ag2CO3
would mask the desired observations

Question 38

test for halides: fluorine

Answer 38

no precipitate

Question 39

test for halides: chlorine

Answer 39

white ppt

Ag+ (aq) + Cl- (aq) -> AgCl (s)

Question 40

test for halides: bromine

Answer 40

cream ppt

Ag+ (aq) + Br- (aq) -> AgBr (s)

Question 41

test for halides: iodine

Answer 41

yellow ppt

Ag+ (aq) + I- (aq) -> AgI (s)

Question 42

what test can you do following the test for halide ions to distinguish ppt formed

Answer 42

add ammonium

of variable concentrations

Question 43

silver chloride in ammonia

Answer 43

dilute: dissolves
conc: dissolves

AgCl (s) + 2NH3 (aq) -> [Ag(NH3)2] + (aq) + Cl- (aq)
colourless solution

Question 44

silver bromide in ammonia

Answer 44

dilute: partially dissolves
conc: dissolves

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

Question 45

silver iodide in ammonia

Answer 45

doesn’t dissolve in any concentration

it is too insoluble