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Chemistry > Group 7 > Flashcards

Group 7 Flashcards

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1
Q

How are the halogens found in nature?

A

As ions bonded to group 1 metals

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2
Q

Describe and explain the trend in boiling points down the group

A

Boiling point increases

More electrons
Stronger London forces
More energy to break

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3
Q

Describe the structure of the halogens when solid and gas

A

Solid = giant molecular lattice

Gas = diatomic molecules

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4
Q

Describe and explain the trend in reactivity down the halogens

A

Reactivity decreases

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

Nuclear charge increases but is outweighed

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5
Q

Describe a halogen-halide displacement reaction

A

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

E.g chlorine displaced iodine from sodium iodide

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6
Q

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

A

Cyclohexane

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7
Q

How does cyclohexane make displaced halogens more visible?

A

Cyclohexane is non-polar

Halogens are non-polar

Dissolves halogens

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8
Q

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

A

Cyclohexane and dissolves halogen form top layer

Bottom layer is water plus salt

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9
Q

Describe and explain the colours of halogens in cyclohexane

A

Chlorine = green

Bromine =. Orange-brown

Iodine= violet

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10
Q

State whether the halogen or halide is oxidised or reduced

A

Halogen = reduced

Halide = oxidised

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11
Q

What colour and state is flourine at RTP

A

Pale Yellow gas

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12
Q

What is a disproportionation reaction?

Give and example

A

When the same species is oxidised and reduced

Chlorine + water/ NaOH

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13
Q

What are the products of chlorine and water?

A

Chloric (1) acid

Hydrochloride acid

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14
Q

How does chloric acid purify water ?

A 
The chlorate (1) ions (ClO-) 
Kill bacteria
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15
Q

What are the disadvantages of adding chlorine to water ?

A

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

Chlorine gas is toxic + respiratory irritant

Ethical dilemma (choice?)

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16
Q

What are the advantages to adding chlorine to water

A

Kills bacteria, eradicate disease

17
Q

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

A

Ozone: short half life so not permanent disinfectant

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

18
Q

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

A

Sodium chlorate, sodium chloride and water

19
Q

Describe how household bleach is produced

A

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

Chlorate (1) ions

20
Q

Describe a use for bromine

A

Photographic film

21
Q

Describe a use for iodine

A

Medical tracers and cancer treatment

22
Q

What is the difference between qualitative and quantitative analysis?

A

Qualitative = what elements are present

Quantitative = how much of each element is present

23
Q

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

A

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

24
Q

Describe the carbonate test

A

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

25
Q

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

A

nitric acid (HNO3)

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

26
Q

Describe and explain the sulphate test

A

Add barium nitrate (Ba(NO3)2)

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

27
Q

Why is barium nitrate used in the sulphate test?

A

Won’t show a false negetive in next tests

Barium chloride will

28
Q

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

A

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

29
Q

Describe the halide test and the results

A

Add acidified silver nitrate

Halogen will displace nitrate to form silver halide precipitate

Cl= white 
Br= cream 
I= yellow
30
Q

Describe and explain the results after adding ammonia to silver halides

A 
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

31
Q

Describe the test for ammonium ions

A

Add warm sodium hydroxide

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

32
Q

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

A

Ammonia gas produced when NaOH added but highly soluble

Heating releases NH3 gas

33
Q

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

A

AgCO3 and AgSO4 will form precipitates (false negatives)

34
Q

Test for copper ions

A

Add pottasium iodide

White precipitate and brown solution formed

Chemistry (28 decks)

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