Inorganic Unit 2.3: Group 7

Question 1

state & explain the trend in electronegativity down group 7 (17)

Answer 1

electronegativity decreases down the group

atomic radius increases
shielding increases
so attraction b/w nucleus & bonding pair of e-s decreases
more difficult to attract bonding pair to atom

Question 2

state & explain the trend in boiling points down group 7(17)

Answer 2

boiling point increases down the group

molecules get bigger
increase in # of e-s
increase surface contact
VDW forces b/w molecules are stronger
so more energy needed to overcome them

Question 3

what is the trend in oxidising power of the halogens?

Answer 3

oxidising power decreases down the group
halogen atom gains an e- when is oxidises the halide ion
atomic radius & shielding increase
so attraction b/w nucleus & outer e-s decreases
so the harder it is to gain an e-

Question 4

complete the table of displacement reactions of halide ions & their equations = oxidising power

Answer 4

see table

Question 5

what is the trend in reducing power of the halide ions?

Answer 5

reducing power of the halide ions increases down the group

halide ions lose an e- when reducing H2SO4
in ionic radius & shielding increase
so attraction b/w nucleus & outer e-s decreases
so the easier it is to lose an e-

Question 6

complete the table of equations, observations & reaction types of the halide ions & H2SO4 = reducing power of halides

Answer 6

see table

Question 7

how can halides be identified using acidified silver nitrate?

Answer 7

add nitric acid
add silver nitrate (aq)
F- no ppt bc AgF is soluble
Cl- white ppt
Br- cream ppt
I- yellow ppt

Question 8

what is the solubility of halide ions in ammonia & equations?

Answer 8

F- soluble in dilute NH3
Cl- soluble in dilute NH3
Br- only soluble in conc. NH3
I- insoluble in conc. NH3

Question 9

why is nitric acid added/why is silver nitrate acidified?

Answer 9

to remove other ions e.g. CO3 2- that could interfere

Question 10

why specifically silver nitrate?

Answer 10

halide ion salts are insoluble so form observable precipitates with different colours

Question 11

why is ammonia solution added?

Answer 11

the white, cream & yellow precipitates look very similar in colour
so ammonia is a follow up test to determine the exact halide ion

Question 12

what is the equation of the reaction of chlorine with cold, dilute, aqueous NaOH?

Answer 12

see sheet

Question 13

what is the use of the Cl2 & NaOH reaction?

Answer 13

sodium chlorate (I) is the active ingredient in bleach

Question 14

why is Cl2 & NaOH a disproportionation reaction?

Answer 14

chlorine is oxidised & reduced simultaneously

Question 15

what is the equation of the reaction of chlorine with water?

Answer 15

see sheet

Question 16

why is chlorine used to treat water?

Answer 16

to kill microorganisms

Question 17

why is chlorine used treat water even though chlorine gas is toxic?

Answer 17

benefits outweigh the risks
only used in small amounts & little Cl2 remains once reacted

Question 18

what is the equation of the reaction of chlorine with water (in sunlight)?

Answer 18

see sheet