8.2 The Halogens Flashcards

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?

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
What happens when chlorine is added to water?
Cl2 + H2O —> HClO + HCl For each chlorine molecule, one chlorine atom is oxidised, the other reduced
26
What kills microorganisms in water when chlorine is added to water?
The products Chloric acid and Hydrochloric acid - Chloric acid also acts as a weak bleach
27
How to show Chloric acid’s bleaching properties
Add universal indicator It will turn red, for the presence of acids Bleaching properties causes colour to disappear
28
What happens when chlorine reacts with cold, dilute aqueous sodium hydroxide?
Cl2 + 2NaOH —> NaClO + NaCl + H2O
29
Use of NaClO
Sodium Chlorate Household bleach
30
Risk of chlorine
Respiratory irritant and toxic gas in large concentrations
31
Danger of adding chlorine to drinking water
Can react with organic hydrocarbons like methane to form chlorinated hydrocarbons These can cause cancer
32
What would happen if chlorine is not added to drinking water?
Quality of drinking water would be compromised Could cause typhoid or cholera outbreak
33
Test for halide ions
Add Silver Nitrate Aqueous halide ions react with aqueous silver ions to form precipitate of silver halides Different colour precipitates are formed
34
In the displacement reactions between halogen and halide ions which is reducing/oxidising agent?
Halogen - gain electrons - oxidising agent Halide ions - lose electrons - reducing agent
35
How can the reducing ability of halide ions be shown?
Reactions with H2SO4, which is a strong oxidising agent
36
Can chloride ions reduce H2SO4?
No - they are not powerful enough
37
Can Bromide ions reduce H2SO4?
Yes - it’s reduced to SO2 2H+ + H2SO4 + 2Br- —> SO2 + Br2 +H2O
38
Can Iodide ions reduce H2SO4?
Yes, they are even more powerful and reduce the SO2 formed to S, which is further reduced to H2S