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A Level - Chemistry > 4B: Elements of group 7 > Flashcards

4B: Elements of group 7 Flashcards

1
Q

How does electronegativity of elements change going down the group?

A

Electronegativity decreases going down the group

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2
Q

What is the physical state of the group 7 elements?

A

F2 - gas
Cl2 - gas
Br2 - liquid
I2 - solid

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3
Q

What is the colour of the group 7 elements?

A

F2- pale yellow
Cl2 - green
Br2 - red-brown
I2 - grey

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4
Q

What is the solubility of halogens?

A

Low solubility in water as non-polar

Soluble in organic compounds

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5
Q

What colour do halogens go in water?

A

Cl2 - virtually colourless
Br2 - yellow/orange
I2 - brown

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6
Q

What colour do halogens go in organic solvents?

A

Cl2 - virtually colourless
Br2 - orange/red
I2 - pink/violet

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7
Q

How does reactivity change going down the group?

A

Becomes less reactive going down the group

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8
Q

What do halogens do in redox reactions?

A

Reduced - gains electrons

Oxidising agents

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9
Q

Why do halogens become less reactive going down the group?

A

Atom size increases therefore shielding increases

Makes it harder for larger atoms to attract other electrons

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10
Q

How does the melting and boiling points change going down the group?

A

Mp/bp increases going down the group

Due to increasing London forces

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11
Q

Why is fluorine difficult to study?

A

It is a toxic gas

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12
Q

Why is astatine difficult to study?

A

Highly radioactive and decays quickly

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13
Q

What is the rule for the displacement of halide ions?

A

More reactive halogen can displace less reactive halide ion

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14
Q

What is the usual oxidation number of a halide ion?

A

-1

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15
Q

Give an example when halide ions have a positive oxidation number?

A

When in a compound with oxygen as it has a higher electronegativity (except F)

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16
Q

How are the halogen elements usually formed?

A

Oxidation of the halide ions in a redox reaction

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17
Q

How can you tell if there has been a displacement of the halides?

A 
Colour change 
(orange for bromine, brown for iodine)
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18
Q

How can you make the colour change more apparent in halide displacement?

A

Mix end solution with organic solvent like hexane

Produces distinct layer of colour

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19
Q

How do halogens react with group 1 metals?

A

2M + X2 -> 2MX
M = metal, X = halogen
M = oxidised, X = reduced

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20
Q

How do halogens react with group 2 metals?

A

M + X2 -> MX2
M = metal, X = halogen
M = oxidised, X = reduced

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21
Q

What happens when a halogen interacts with a cold alkali?

A

Disproportionation

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22
Q

What is the equation for the disproportionation of halogens in cold alkali?

A

X2 + 2NaOH -> NaOX + NaX + H20

X = halogen

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23
Q

What is the chemical formula of bleach?

A 
NaClO
Sodium Chlorite (I)
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24
Q

What is the reaction to form bleach?

A

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

Disproportionation

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25
Q

What is the use of sodium chlorite?

A

Water treatment

Bleach textiles and paper

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26
Q

What is a XO- ion?

X = halogen

A

Halate(I) ion

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27
Q

At what temperature is an alkali said to be hot?

28
Q

What is the reaction between a halogen and a hot alkali?

A

3X2 + 6NaOH -> NaXO3 + 5NaX + 3H2O

29
Q

What should be done when chlorine is produced in a reaction?

A

Carry the experiment out in a fume cupboard as its toxic

30
Q

Why does fluorine have so little uses?

A

Extremely reactive

31
Q

What is the use of sodium fluoride?

A

Strengthen enamel (found in fluoride toothpaste)

32
Q

What is the compound polytetrafluoroethene (PTFE)?

A

Used in non-stick surfaces like on frying pans

33
Q

What is the use of chlorine?

A

Kills bacteria in water

Polyvinlychloride (PVC)

34
Q

What is the reaction which causes chlorine to kill bacteria?

A

Cl2 + H2O -> HCl (aq) + HClO (aq)
HClO + H2O ClO- + H3O+
ClO- kills bacteria

35
Q

What is the name of the substance HClO?

A

Hypochlorous acid

36
Q

What is the use of PVC?

A

Plastic used for doors and windows

37
Q

What is the use of sodium chlorate(V)?

A

Powerful weed-killer

38
Q

Why does elemental bromine not have many uses?

A

It is a very corrosive liquid

39
Q

What is the use of potassium bromide?

A

A sedative

40
Q

What is the use of iodine?

A

Important antiseptic

41
Q

What is the use of potassium iodide?

A

Sometimes added to salt

Lack of iodine leads to the disease goitre

42
Q

How does the reducing power of halides change down the group?

A

Reducing power increases

loses electron easier

43
Q

Why does reducing power increase going down the group?

A

Easier to lose electron as:
Electrons further away from nucleus
Extra shells means increased shielding
Effective nuclear charge doesn’t change

44
Q

What is the product when a halide reacts with sulphuric acid?

A

Hydrogen halide

45
Q

What are the reactions of KF/KCl with H2SO4?

K = unspecified ion

A

KF/Cl (s) + H2SO4 (l) -> KHSO4 (s) + HF/Cl (g)

46
Q

When a hydrogen halide is produced what is observed?

A

Misty fumes are produced

47
Q

When F-/Cl- ions react with H2SO4 is it a redox reaction?

A

No - oxidation numbers of halide and sulphur stay the same

48
Q

When F-/Cl- ions react with H2SO4 why is there not another reaction?

A

F-/Cl- ions aren’t strong enough to reduce the sulphuric acid

49
Q

What is the reaction between KBr and H2SO4?

K = unspecified ion

A

KBr (s) + H2SO4 (l) -> KHSO4 (s) + HBr (g)

2HBr + H2SO4 -> Br2 (g) +SO2 (g) + 2H2O (l)

50
Q

Why can the second step happen when KBr reacts with H2SO4?

A

Br- is a stronger reducing agent than Cl-

Reacts with H2SO4 in a redox reaction

51
Q

What would you observe if bromine gas is produced?

A

Orange fumes

52
Q

What is noteworthy about SO2?

A

They are choking fumes

Experiments with thus as a product should be done in a fume cupboard

53
Q

What is the reaction between KI and H2SO4?

K = unspecified ion

A

KI (s) + H2SO4 (l) -> KHSO4 (s) + HI (g)

2HI + H2SO4 -> I2 (g) +SO2 (g) + 2H2O (l)

6HI + SO2 -> H2S + 3I2 +2H2O

54
Q

Why can the second & third step happen when KI reacts with H2SO4?

A

As very strong reducing agent

It can reduce SO2 whereas Br- cannot

55
Q

What is noteworthy about the gas H2S?

A

Toxic gas that smells of rotten eggs

56
Q

What colour are hydrogen halides?

A

Colourless

57
Q

What happens when hydrogen halides dissolve in water?

X = halide

A

HX + H20 -> H3O+ +X-

Ionic: HCl -> H+ + Cl-
This is the formation of a hydrohalide acid

58
Q

How do hydrogen halides react with ammonia gas?

A

NH3 + HX -> NH4X (s)

Produces white fumes

59
Q

What is the test for halides?

A

Add dilute nitric acid to remove other ions
Add silver nitrate (AgNO3)
Precipitate of silver halide formed

60
Q

What is the ionic equation for the test for halides?

A

Ag+ (aq) + X- (aq) -> AgX (s)

61
Q

What colour precipitate is formed for each halide in the standard halide test?

A 
F- = No precipitate (AgF is soluble)
Cl- = White 
Br- = Cream
I- = Yellow
62
Q

What can be done to identify the halide ion after the silver nitrate test?

A

Adding ammonia solution

If it dissolves then it will go colourless

63
Q

What occurs when ammonia solution is added after the silver nitrate test?

A 
Cl- = Precipitate dissolves in dilute ammonia
Br- = Dissolves in conc. ammonia, not in dilute
I- = precipitate will not dissolve
64
Q

What is the test for SO2?

A

Potassium dichromate paper turns from orange to green

65
Q

What is the test for H2S?

A

Turns lead ethanoate paper from white to black

66
Q

What is the affect of light after the silver nitrate test?

A 
Cl- = Purple
Br- = Green
I- = No change

A Level - Chemistry (26 decks)

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