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Chemistry > Group 7 > Flashcards

Group 7 Flashcards

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1
Q

what are group 7 elements known as

A

the halogens

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2
Q

how many outer electrons do group 7 elements have

A

7

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3
Q

why are group 7 elements in the p block

A

their outer electrons are in the p subshell

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4
Q

what do group 7 elements exist as

A

diatomic molecules

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5
Q

what is the trend in atomic radius down the group

A

increases

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6
Q

why does atomic radius increase down the group

A
  • more shells-more shielding
  • nuclear attraction on outer electrons decreases
  • atomic radius increases
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7
Q

why is the ionic radius of a group 7 element bigger than the atomic radius

A
  • atoms gain electrons to form x- ions
  • same protons more electrons
  • more electron-electron repulsion
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8
Q

trend in boiling point down group 7

A

increases

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9
Q

what is the trend in volatility down the group

A

they become less volatile

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10
Q

why does boiling point increase (and volatility decrease) down group 7

A

-Mr increases- more electrons
_VDW forces between molecules increases
-more energy needed to overcome forces of attraction

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11
Q

trend in electronegativity down group

A

decreases

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12
Q

why does electronegativity decrease down group

A
  • more shells- more shielding

- nuc attraction on outer electron decreases as atomic radius increases

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13
Q

trend in first ionisation energy down group

A

decreases

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14
Q

why does first ionisation energy decrease

A
  • more shells- more shielding

- nuc attraction on outer electron decreases as atomic radius increases

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15
Q

appearance of chlorine

A

pale green gas

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16
Q

state of chlorine at room temperature

A

gas

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17
Q

colour of aqueous solution of chlorine

A

very pale green

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18
Q

colour of chlorine in cyclohexane

A

very pale green

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19
Q

appearance of bromine

A

red/brown liquid

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20
Q

state of bromine at room temp

A

liquid

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21
Q

colour of bromine in aqueous solution

A

orange

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22
Q

colour of bromine in cyclohexane

A

orange

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23
Q

appearance of iodine

A

grey solid

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24
Q

state of iodine at room temp

A

solid

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25
Q

colour of iodine in aqueous solution

A

brown

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26
Q

colour of iodine in cyclohexane

A

purple

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27
Q

why are halogens more soluble in cyclohexane than water

A

they themselves are non polar like cyclohexane

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28
Q

trend in solubility of halogen in water down group

A

decreases

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29
Q

why does solubility in water decrease down group

A

halogen molecule becomes larger

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30
Q

what does a series of displacement reactions provide evidence for

A

the trend in oxidising powers of the halogens

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31
Q

method for displacement reactions

A
  • add solution of each halogen to a solution of potassium halide in turn
  • note any colour changes and decide whether a reaction has occurred
  • add cyclohexane and note the clour in the organic (top layer)
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32
Q

what will the colour of the organic layer in displacement reactions tell you

A

which halogen is now present

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33
Q

colour of organic top layer:

KBr + Cl2

A

orange- Br2

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34
Q

colour of organic top layer:

KI + Cl2

A

pink/purple - I2

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35
Q

colour of organic top layer:

KCl + Br2

A

orange- Br2

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36
Q

colour of organic top layer:

Br2 + KI

A

purple/pink- I2

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37
Q

colour of organic top layer:

I2 + KCl

A

purple/pink- I2

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38
Q

colour of organic top layer:

KBr + I2

A

pink/purple- I2

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39
Q

oxidising agent

A

substance which accepts electrons

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40
Q

why are halogens oxidising agents

A

they all take electrons readily to form ions

X2 +2e- > 2X-

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41
Q

what happens to the halogens ability to act as oxidising agents as you go down the group

A

decreases

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42
Q

why does halogens ability to act as oxidising agents decrease down group

A
  • become less reactive down group
  • chlorine is smallest atom (out of chlorine, bromine, iodine)
  • has strongest nuc attraction on outer electrons (fewer shells)
  • best at gaining electrons
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43
Q

trend in reactivity Cl2 > Br2 > I2

A

chlorine most reactive- iodine least

44
Q

if X is higher up in group than Y…

A

X is able to oxidise Y

45
Q

what is a reducing agent

A

electron donor (is itself oxidised)

46
Q

can halide ions act as reducing agents

A

yes but to different extents

47
Q

what is the oxidation number of sulphur in sulphuric acid

A

+6

48
Q

test for sulphuric acid

A

indicator paper turns red

49
Q

oxidation number of sulphur in sulphur dioxide

A

+4

50
Q

test for sulphur dioxide

A

acidified dichromate paper: orange > green

51
Q

oxidation number of sulphur in its element

A

0

52
Q

test for sulphur

A

yellow solid

53
Q

oxidation number of sulphur in hydrogen sulphide

A

-2

54
Q

test for hydrogen sulphide

A

lead acetate paper: white > black

55
Q

what happens to the halide ion if sulphuric acid is reduced by it

A

it will be oxidised to the halogen molecule X2

2X- > X2 + 2e-

56
Q

method to react halide on with sulphuric acid

A
  • put 0.1g solid halide compound in test tub
  • add 10 drops conc. sulphuric
  • warm if necessary
  • identify products
57
Q

initial observations NaCl + sulphuric

A

white fumes (HCl made)

58
Q

subsequent observations NaCl + sulphuric

A

no further change

59
Q

initial observation: NaBr + sulphuric

A

white fumes (HBr)

60
Q

subsequent observations: NaBr + sulphuric

A

brown fumes (Br2)

SO2 detected

61
Q

initial observation: NaI + sulphuric

A

white fumes (HI)

62
Q

subsequent observations: NaI + sulphuric

A

purple fumes (I2)

SO2,S, H2S all detected

63
Q

what is the initial observation in all halide ion and sulphuric acid reactions

A

white fumes

64
Q

what are the white fumes

A

the hydrogen halide as a gas

65
Q

why is NaCl + H2SO4 not a redox reaction

A
  • no change in oxidation states

- example of proton transfer ie acid/base reaction

66
Q

why is there no further reaction between HCl produced and sulphuric acid

A

chloride ion cannot reduce sulphuric acid

67
Q

why can halides act as reducing agents

A

they are able to lose electrons to form the respective halogen

68
Q

what is the trend in reducing strength down the group of halides

A

increases

69
Q

why does reducing strength of halides increase down group

A

-they become less good at holding onto their electrons (size increases, attraction on outer electrons decreases)

70
Q

strongest oxidising agent group 7

A

flourine

71
Q

strongest reducing agent group 7

A

iodide

72
Q

test for halide ions

A
  • make a solution of the substance to be tested
  • add dilute nitric acid to remove other ions that interfere with test results by giving precipitates
  • add silver nitrate solution
  • observe colour of precipitate
73
Q

Cl- PPT colour

A

white

74
Q

name and formula of PPT that Cl- forms

A

silver chloride

AgCl

75
Q

Br- PPT colour

A

cream

76
Q

name and formula of PPT that Br- forms

A

silver bromide

AgBr

77
Q

I- PPT colour

A

yellow

78
Q

name and formula of PPT that I- forms

A

silver iodide

AgI

79
Q

why do F- ions not form a ppt with silver nitrate

A

silver fluoride is soluble in water

80
Q

Overall equation silver nitrate and sodium chloride

A

AgNO3 + NaCl > AgCl + NaNO3

81
Q

Ionic equation silver nitrate + sodium chloride

A

Ag + Cl > AgCl

82
Q

General ionic equation for test for halide ions

A

Ag + X > AgX

83
Q

How to test for trends in solubility of the silver halide precipitates

A

Add dilute ammonia solution to each PPT and see if it dissolves

If not, add conc ammonia solution and see if it dissolves

84
Q

What is silver chlorides solubility in ammonia

A

Soluble in dilute NH3

85
Q

What is silver bromides solubility in ammonia

A

Insoluble in dilute NH3

Soluble in conc NH3

86
Q

What is silver iodides solubility in ammonia

A

Insoluble in dilute and conc NH3

87
Q

What is the trend in solubility in ammonia solution from silver chloride to silver iodide

A

Decreasing soluble

88
Q

What does the use of ammonia solution help to distinguish between

A

Silver halide precipitates when the difference between their colours is not easy to identify

89
Q

Disproportionation

A

A redox reaction in which the same element is both oxidised and reduced

90
Q

Equation for the reaction of chlorine with water

A

Cl2 + H20 > HCl + HClO
<

(Reversible)

91
Q

Where is an equilibrium established between in the reaction between chlorine and water

A

The chlorine, water, hydrochloric acid and chloric (I) acid

92
Q

What is chlorine in the reaction between the reaction of chlorine and water

A

Both oxidised and reduced

93
Q

How can chlorine be detected

A

Very pale green colour

94
Q

How can hydrochloric acid be detected

A

Turns universal indicator paper red

95
Q

How can chloric (I) acid be detected

A

Universal indicator paper red then bleached white

96
Q

What happens to the chloric acid that is formed from the reaction between chlorine and water

A

Decomposes to hydrochloric acid and oxygen

97
Q

Equation for decomposition of chloric (I) acid

A

2HClO > 2HCl + O2

98
Q

What is the reaction between chlorine and water accelerated by

A

Sunlight and certain catalysts

99
Q

Why is the reaction between chlorine and water accelerated by sunlight

A

Breaks bonds so lowers activation energy

100
Q

What is produced when chlorine reacts with water in the presence of sunlight

A

Hydrochloric acid and oxygen

101
Q

What is the benefit of using chlorine in water treatment

A

It kills bacteria

102
Q

What is the risk in using chlorine in water treatment

A

It’s toxic

Chlorinated hydrocarbons are carcinogenic

103
Q

What does the reaction of chlorine with cold dilute sodium hydroxide solution produce

A

Sodium chloride, sodium chlorate (I) and water

104
Q

Equation for reaction between chlorine and sodium hydroxide solution

A

Cl2 + NaOH > NaCl + NaClO + H2O

105
Q

What happens to the colour and smell of the chlorine during the reaction between it and NaOH solution

A

The green colour fades and the smell is less pungent

106
Q

Why is the reaction between chlorine and sodium chloride a disproportionation reaction

A

Chlorine is both oxidised and reduced

107
Q

Main use of sodium chlorate

A

Domestic bleach

Chemistry (42 decks)

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