5. group 7 - the halogens

Question 1

halogen exist as

Answer 1

diatomic molecules (2 atoms joined by a single covalent bond)

Question 2

halogens bpt and mpt ____ down the group

Answer 2

increase

Question 3

why does the bpt and mpt of halogens increase down the group

Answer 3

increasing strength of the LDF

size and relative mass of atoms increases

Question 4

where is the mpt and bpt of halogens increasing shown

Answer 4

changes of physical state 
from chlorine (gas) to iodene (solid)

Question 5

what does volatile mean

Answer 5

low boiling point

evaporates / turns to gas easily

Question 6

halogens get more or less reactive down the group

Answer 6

less

Question 7

how do halogens react

Answer 7

by gaining an electron in their outer shell to form 1- ions

they are reduced RIG

Question 8

why are halogens ‘oxidising agents’

Answer 8

as they’re reduced they oxidise another substance (redox)

Question 9

halogens get more or less reactive down the group?

Answer 9

less reactive

Question 10

why doe halogens get less reactive down the group?

Answer 10

down group atomic radii increases
outer electrons further from nucleus
outer electrons shielded more from attraction of + nucleus because there are more inner electrons.
harder for larger atoms to attract the electron needed to form an ion
(despite increased charge on nucleus)

Question 11

‘halide’ is used to describe

Answer 11

halogen 1- ion

Question 12

when can the halogens relative oxidising strengths be seen

Answer 12

in their displacement reactions with halide ions

Question 13

halogens displace lee or more reactive halide ions fom solution?

Answer 13

halogens displace less reactive halide ions from solution

Question 14

e.g. mix bromine water Br2(aq) with potassium iodide solution KI(aq)
Br2(aq) + 2KI(aq) ->

Answer 14

bromine (more reactive) displaces/oxidises iodide ions (less reactive)
giving iodine I2 and potassium bromide solution KBr
2KBr(aq) + I2 (aq)

Question 15

what observation can be made when a displacement reaction takes place?

Answer 15

colour change

Question 16

how can you make the colour change easier to see in a displacement reaction

Answer 16

shake reaction mixture with an organic solvent e.g. hexane

halogen present dissolves and settles in a distinct layer above aqueous solution

Question 17

chlorine water Cl2(aq) (colourless) combine with KCl(aq) (colourless)

1. in aqueous solution
2. in organic solution

Answer 17

1. no reaction - colourless

2. no reaction - colourless

Question 18

chlorine water Cl2(aq) (colourless) combine with KBr(aq) (colourless)

1. in aqueous solution
2. in organic solution

Answer 18

1. yellow (Br2)

2. Orange (Br2)

Question 19

chlorine water Cl2(aq) (colourless) combine with KI(aq) (colourless)

1. in aqueous solution
2. in organic solution

Answer 19

1. Orange/Brown (I2)

2. Purple (I2)

Question 20

Bromine water Br2(aq) (yellow) combine with KCl(aq) (colourless)

1. in aqueous solution
2. in organic solution

Answer 20

1. no reaction (yellow)

2. no reaction (orange)

Question 21

Bromine water Br2(aq) (yellow) combine with KBr(aq) (colourless)

1. in aqueous solution
2. in organic solution

Answer 21

1. no reaction (yellow)

2. no reaction (orange)

Question 22

Bromine water Br2(aq) (yellow) combine with KI(aq) (colourless)

1. in aqueous solution
2. in organic solution

Answer 22

1. orange/brown (I2)

2. Purple (I2)

Question 23

Iodine solution I2(aq) (orange/brown) combine with KCl(aq) (colourless)

1. in aqueous solution
2. in organic solution

Answer 23

1. no reaction (orange/brown)

2. no reaction (purple)

Question 24

Iodine solution I2(aq) (orange/brown) combine with KBr(aq) (colourless)

1. in aqueous solution
2. in organic solution

Answer 24

1. no reaction (orange/brown)

2. no reaction (purple)

Question 25

Iodine solution I2(aq) (orange/brown) combine with KI(aq) (colourless)

1. in aqueous solution
2. in organic solution

Answer 25

1. no reaction (orange/brown)

2. no reaction (purple)

Question 26

a halogen will displace/oxidise a halide from solution if the halide is

Answer 26

below it in the periodic table

Question 27

how to test for halides

Answer 27

1. add dilute nitric acid to remove ions that might interfere with test
2. add silver nitrate solution AgNO3(aq)
3. precipitate forms of the silver halide
4. colour of precipitate identifies halide
5. test results by adding ammonia solution (silver halides have different solubility’s in ammonia. larger the ion the more difficult to dissolve)

Question 28

silver nitrate test for halide ions. Chloride Cl -

1. precipitate colour
2. adding NH3(aq)

Answer 28

1. white

2. dissolves in dilute NH3(aq)

Question 29

silver nitrate test for halide ions. Bromide Br-

1. precipitate colour
2. adding NH3(aq)

Answer 29

1. cream

2. dissolves in concentrated NH3(aq)

Question 30

silver nitrate test for halide ions. Iodide I-

1. precipitate colour
2. adding NH3(aq)

Answer 30

1. yellow

2. insoluble in concentrated NH3 (aq)