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OCR Gateway A Level Chemistry > 8.2 The Halogens > Flashcards

8.2 The Halogens Flashcards

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1
Q

What is the most reactive non metallic group?

A

Group 17

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2
Q

How are the group 17 elements found in nature?

A

Stable halide ions dissolved in sea water
Combined with Sodium and Potassium as solid deposits

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3
Q

How do halogens exist at RTP?

A

Diatomic molecules

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4
Q

Appearance of F2

A

Pale yellow gas

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5
Q

Appearance of Cl2

A

Pale green gas

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6
Q

Appearance of Br2

A

Red brown liquid

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7
Q

Appearance of I2

A

Shiny grey black solid

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8
Q

Appearance of At2

A

Never been seen

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9
Q

What happens to boiling point going down group 17?

A

Boiling point increases

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10
Q

Why does boiling point increase going down group 17?

A

More electrons
Stronger London forces
More energy required to break the intermolecular forces
Boiling point increases

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11
Q

Outer shell electrons in halogens?

A

7 electrons
2 in the s sub shell
5 in the p sub shell

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12
Q

Most common reaction for halogens

A

Redox reactions

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13
Q

What happens to halogens during redox reactions?

A

Each Halogen atom is reduced, gaining an electron, forming a 1- ion
Acts as an oxidising agent, oxidising another species

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14
Q

What happens to reactivity of halogens going down the group?

A

Reactivity decreases

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15
Q

What happens during halogen-halide displacement reactions?

A

A more reactive halogen displaces a less reactive halogen in a compound

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16
Q

Experiment to show reactivity of halogens

A

Solution of each halogen is added to aqueous solutions of other halides
If halogen added is more reactive than the halide, displacement reaction takes place
Solution changes colour

17
Q

How can you tell apart bromine and iodine in water?

A

Organic non polar solvent like cyclohexane can be added and mixture is shaken
Non polar halogens dissolve more readily in cyclohexane than water
Here, the colours are easier to tell apart
Bromine - orange
Iodine - purple

18
Q

Reactivity of Fluorine

A

Reacts with almost any substance it comes into contact with

19
Q

Reactivity of Astatine

A

Radioactive - decays rapidly
Element has never been seen, but predicted to be most reactive halogen

20
Q

Explain trend in reactivity going down group 7

A

Atomic radius increases
More inner shells so electron shielding is increased
Less nuclear attraction to attract an electron from another species
Reactivity decreases going down the group

21
Q

Which halogen is the strongest oxidising agent?

A

Fluorine

22
Q

What is a disproportionation reaction?

A

A redox reaction where the same element is both oxidised and reduced

23
Q

Examples of disproportionation reactions

A

Chlorine and water
Chlorine and cold, dilute Sodium Hydroxide

24
Q

Why is chlorine used in water treatment?

A

Reducing prevalence of waterborne diseases by killing harmful bacteria

25
Q

What happens when chlorine is added to water?

A

Cl2 + H2O —> HClO + HCl
For each chlorine molecule, one chlorine atom is oxidised, the other reduced

26
Q

What kills microorganisms in water when chlorine is added to water?

A

The products Chloric acid and Hydrochloric acid -
Chloric acid also acts as a weak bleach

27
Q

How to show Chloric acid’s bleaching properties

A

Add universal indicator
It will turn red, for the presence of acids
Bleaching properties causes colour to disappear

28
Q

What happens when chlorine reacts with cold, dilute aqueous sodium hydroxide?

A

Cl2 + 2NaOH —> NaClO + NaCl + H2O

29
Q

Use of NaClO

A

Sodium Chlorate
Household bleach

30
Q

Risk of chlorine

A

Respiratory irritant and toxic gas in large concentrations

31
Q

Danger of adding chlorine to drinking water

A

Can react with organic hydrocarbons like methane to form chlorinated hydrocarbons
These can cause cancer

32
Q

What would happen if chlorine is not added to drinking water?

A

Quality of drinking water would be compromised
Could cause typhoid or cholera outbreak

33
Q

Test for halide ions

A

Add Silver Nitrate
Aqueous halide ions react with aqueous silver ions to form precipitate of silver halides
Different colour precipitates are formed

34
Q

In the displacement reactions between halogen and halide ions which is reducing/oxidising agent?

A

Halogen - gain electrons - oxidising agent
Halide ions - lose electrons - reducing agent

35
Q

How can the reducing ability of halide ions be shown?

A

Reactions with H2SO4, which is a strong oxidising agent

36
Q

Can chloride ions reduce H2SO4?

A

No - they are not powerful enough

37
Q

Can Bromide ions reduce H2SO4?

A

Yes - it’s reduced to SO2
2H+ + H2SO4 + 2Br- —> SO2 + Br2 +H2O

38
Q

Can Iodide ions reduce H2SO4?

A

Yes, they are even more powerful and reduce the SO2 formed to S, which is further reduced to H2S

OCR Gateway A Level Chemistry (46 decks)

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