Group 7

Question 1

How are the halogens found in nature?

Answer 1

As ions bonded to group 1 metals

Question 2

Describe and explain the trend in boiling points down the group

Answer 2

Boiling point increases

More electrons
Stronger London forces
More energy to break

Question 3

Describe the structure of the halogens when solid and gas

Answer 3

Solid = giant molecular lattice

Gas = diatomic molecules

Question 4

Describe and explain the trend in reactivity down the halogens

Answer 4

Reactivity decreases

Atomic radius and shielding increases (repulsion)
Harder to attract electron (feels less attraction by nucleus)

Nuclear charge increases but is outweighed

Question 5

Describe a halogen-halide displacement reaction

Answer 5

A more reactive halogen with displace a less reactive halide from its compound

E.g chlorine displaced iodine from sodium iodide

Question 6

What is added it a halogen -halide displacement reaction to make the products more visible ?

Answer 6

Cyclohexane

Question 7

How does cyclohexane make displaced halogens more visible?

Answer 7

Cyclohexane is non-polar

Halogens are non-polar

Dissolves halogens

Question 8

Describe the layers of a halogen-halide displacement reaction when cyclohexane is added. Explain why

Answer 8

Cyclohexane and dissolves halogen form top layer

Bottom layer is water plus salt

Question 9

Describe and explain the colours of halogens in cyclohexane

Answer 9

Chlorine = green

Bromine =. Orange-brown

Iodine= violet

Question 10

State whether the halogen or halide is oxidised or reduced

Answer 10

Halogen = reduced

Halide = oxidised

Question 11

What colour and state is flourine at RTP

Answer 11

Pale Yellow gas

Question 12

What is a disproportionation reaction?

Give and example

Answer 12

When the same species is oxidised and reduced

Chlorine + water/ NaOH

Question 13

What are the products of chlorine and water?

Answer 13

Chloric (1) acid

Hydrochloride acid

Question 14

How does chloric acid purify water ?

Answer 14

The chlorate (1) ions (ClO-) 
Kill bacteria

Question 15

What are the disadvantages of adding chlorine to water ?

Answer 15

Chlorinated hydrocarbons (e.g methane from decaying organic matter) are carcinogenic

Chlorine gas is toxic + respiratory irritant

Ethical dilemma (choice?)

Question 16

What are the advantages to adding chlorine to water

Answer 16

Kills bacteria, eradicate disease

Question 17

What are the alternatives to adding chlorine to water and why are these not used?

Answer 17

Ozone: short half life so not permanent disinfectant

UV : water may get contaminate down stream, no way to purify then

Question 18

What are the products of the reaction between chlorine and sodium hydroxide?

Answer 18

Sodium chlorate, sodium chloride and water

Question 19

Describe how household bleach is produced

Answer 19

Reacting sodium hydroxide with chlorine to produce sodium chlorate (1)

Chlorate (1) ions

Question 20

Describe a use for bromine

Answer 20

Photographic film

Question 21

Describe a use for iodine

Answer 21

Medical tracers and cancer treatment

Question 22

What is the difference between qualitative and quantitative analysis?

Answer 22

Qualitative = what elements are present

Quantitative = how much of each element is present

Question 23

State the order qualitative analysis should be carried out on an unknown sample

Answer 23

Carbonate test
Sulphate rest
Halide test (silver nitrate and then ammonia)
Ammonium test

Question 24

Describe the carbonate test

Answer 24

Add acid to sample
Bubble gas produced through line water (saturated Ca(OH)2 solution)

Will turn cloudy due to calcium carbonate precipitate if CO3(2-) present

Question 25

What acids can and can’t be used in the carbonate test and why

Answer 25

nitric acid (HNO3)

Not sulphuric acid or hydrochloric acid
Will produce false negetive for sulphate or halide test

Question 26

Describe and explain the sulphate test

Answer 26

Add barium nitrate (Ba(NO3)2)

Barium sulphate precipitate (white) will form
Only sulphate which is insoluble

Question 27

Why is barium nitrate used in the sulphate test?

Answer 27

Won’t show a false negetive in next tests

Barium chloride will

Question 28

Why is the sulphate test carried out after the carbonate test?

Answer 28

Barium carbonate will form a white precipitate so will give false negative

Question 29

Describe the halide test and the results

Answer 29

Add acidified silver nitrate

Halogen will displace nitrate to form silver halide precipitate

Cl= white 
Br= cream 
I= yellow

Question 30

Describe and explain the results after adding ammonia to silver halides

Answer 30

Cl= clear
Br= clear
I= Cloudy 

AgCl and AgBr= polar
Ammonia = polar (like dissolves like)

AgI non-polar because not big enough difference in electronegativity

Question 31

Describe the test for ammonium ions

Answer 31

Add warm sodium hydroxide

Test with damp red litmus paper (will go blue if positive)

Question 32

Why is warm NaOH used in the test for ammonium ions?

Answer 32

Ammonia gas produced when NaOH added but highly soluble

Heating releases NH3 gas

Question 33

Why must the halide test be carried out after the carbonate and sulphate test?

Answer 33

AgCO3 and AgSO4 will form precipitates (false negatives)

Question 34

Test for copper ions

Answer 34

Add pottasium iodide

White precipitate and brown solution formed