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A-level Chemistry Yr 12 Mine > 8 - Reactivity Trends > Flashcards

8 - Reactivity Trends Flashcards

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1
Q

How do halogens exist and why?

A

The exist as Diatomic molecules and this is due to them being highly reactive.

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2
Q

What is the trend in boiling/melting points for halogens?

A

Boiling and melting points increase down the group.

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3
Q

What does volatile mean?

A

A substance is said to be volatile if it has a low boiling point.

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4
Q

What ions do halogens form?

A

The react by gaining one electron, forming 1- ions.

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5
Q

What type of agent are halogens and why?

A

Oxidising agent as they are being reduced so are causing another element to be oxidised (gain electrons).

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6
Q

What is the most common type of reaction for halogens and an example?

A

Redox reactions
Cl2 + 2e- –> 2Cl-

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7
Q

What is the trend in reactivity for the halogens?

A

Halogens are less reactive down the group.

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8
Q

Why do halogens decrease in reactivity down the group?

A

Halogens want to gain one electron and electrons are attracted to the positive nuclease attraction. Therefore the larger positive nuclease attraction the more reactive the halogen. So as you go down the group the atomic radius increases and more inner shells so electron shielding increases. Both causing less nuclear attraction to capture an electron from another species.

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9
Q

What is F2 appearance and state at RTP?

A

Pale yellow gas

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9
Q

What is Cl2 appearance and state at RTP?

A

Pale green gas

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10
Q

What is Br2 appearance and state at RTP?

A

Red-Brown liquid

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11
Q

What is I2 appearance and state at RTP?

A

Shiny grey-black solid

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12
Q

Why do halogens increase in boiling point down the group?

A

There are more electrons meaning there is stronger London forces. So there is more energy required to break the intermolecular forces, causing the boiling point to increase.

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13
Q

What does disproportionation mean?

A

Disproportionation is a redox reaction in which the same element is both oxidised and reduced.

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14
Q

What are the two types of disproportionation reactions for halogens, you need to know and why there used?

A
  1. The reaction of chlorine with water as used in water treatment.
  2. The reaction of chlorine with cold, dilute aqueous sodium hydroxide, as used to form bleach.
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15
Q

What is the equation for household bleach?

A

NaClO

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16
Q

How does a halogen-halide displacement reaction take place?

A

If the halogen added is more reactive than the halide present.

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17
Q

Explain the practical for halogen-halide displacement reaction?

A
  • A reaction takes place, the halogen displacing the halide from solution
  • The solution changes colour.
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17
Q

Explain a halogen-halide displacement reaction?

A
  • A reaction takes place, the halogen displacing the halide from solution
  • The solution changes colour.
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18
Q

What are the results from the halogen displacement reaction practical?

A

Chlorine (Cl2) has reacted with both Br- and I-.
Bromine (Br2) has reacted with I- only.
Iodine (I2) has not reacted with any.

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19
Q

What is the colour change of Br- with Chlorine?

A

Orange colour.

20
Q

What is the colour change of I- with Chlorine and Bromine?

A

Violet colour.

21
Q

What are the benefits for using chlorine in water treatment?

A

Bacteria is killed so the water is fit to drink.
Stops diseases such as typhoid and cholera breaking out.

22
Q

What are the risks for using chlorine in water treatment?

A

Chlorine is an extremely toxic gas: in small doses is respiratory irritant and large doses is fatal.
Can form chlorinated hydrocarbons which are suspected of causing cancer.

23
Q

Why is silver used in the test for the test for halide ions?

A

Halide ions react with silver ions to form precipitates of silver halides.

24
Q

What is the general equation for halide ions and silver ions?

A

Ag+ (aq) + X- (aq) —> AgX (s)

25
Q

What ions do group 2 elements form?

A

2+ ions

26
Q

What agent are group 2 elements and why?

A

Reducing agents as they have caused for another species to be reduced and the group 2 element is oxidised.

27
Q

What is the most common reaction for group 2 elements?

A

Redox reactions

28
Q

What do group 2 elements from when they react with oxygen?

A

Form a metal oxide.

29
Q

What do group 2 elements from when they react with water?

A

An alkaline hydroxide and Hydrogen Gas

30
Q

What do group 2 elements from when they react with dilute acids?

A

Salt and hydrogen

31
Q

What is the general formula for a group 2 metal with oxygen? (Let M be a group 2 metal)

A

M(2+) + O2(2-) —> MO

32
Q

What is the general formula for a group 2 metal with water? (Let M be a group 2 metal)

A

M + H2O —> M(OH)2 + H2

33
Q

What is the general formula for a group 2 metal with Dilute Acid?

A

Metal + Acid —> Salt + Hydrogen

34
Q

What is the trend in reactivity down group 2?

A

Reactivity increases

35
Q

What is the trend down group 2 for solubility, alkalinity and pH level?

A

Increase down the group.

36
Q

Explain how alkalinity / pH level increases down group 2? (Hint:Solubility)

A

The solubility of the hydroxide in water increase down group 2, resulting in the solution containing more OH- ions. Hydroxide ions (OH-) in a solution cause alkalinity. Therefore alkalinity increases down the group therefore as increasing the pH level (high pH more alkaline).

37
Q

Explain why reactivity increases down group 2?

A

As the atomic radius increases this means there is less nuclear attraction on the outermost electron, more electron shielding resulting electrons being even further from the nucleus attraction. All leading to the outermost electron being more easily lost.

38
Q

How are group 2 compounds used as bases in Agriculture?

A

To neutralise acid in soils.

39
Q

How are group 2 compounds used as bases in Medicine?

A

As ‘antacids’ in treating indigestion. (Neutralise excess stomach acid).

40
Q

What fields are some group 2 compounds as bases?

A

Agriculture and Medicine

41
Q

What is the group 2 compound base used in Agriculture?

A

Ca(OH)2

42
Q

What is the group 2 compound base used in Medicine?

A

Mg(OH)2 and CaCO3

43
Q

How do you test for carbonates?

A

Add an dilute acid (like dilute hydrochloric acid) to your mystery sample, then the carbon dioxide will be released. This gas released will turn lime water cloudy.

44
Q

How do you test for sulphates?

A

Add dilute HCl followed by barium chloride solution (BaCl2). If you get a white precipitate it’ll be barium sulfate, then the mastery substance must be a sulfate.

45
Q

How do you test for halides?

A

Add nitrate acid, then silver nitrate solution. If chloride, bromide and iodide is present, a precipitate will form:
Silver chloride is a white precipitate
Silver bromide is a cream precipitate
Silver iodide is a yellow precipitate

46
Q

How do you test for ammonium compounds?

A

Add some sodium hydroxide to your mystery substance in a test tube and warm the mixture. If ammonia (NH3) gas is given off by using a damp piece of red litmus paper will turn the paper blue.

47
Q

What is the most effective way in order to test form: halides, carbonates and sulfates. And not get false positive results?

A
  1. Test for Carbonates
  2. Test for sulfates
  3. Test for halides
48
Q

Explain why you do the test in order of carbonates to sulphates to halides.

A

Aswell as barium sulphate, barium carbonate is also insoluble. So if your testing for sulfate ions, you want to make to make sure there are no carbonate ions around first, or both will form a white precipitate in the test for sulfates.
If testing for halide ion, you want to rule out the presence of sulfate ion first, as sulfate ions will also produce a precipitate with silver nitrate. To get around this you can first add a dilute acid to your test solution, the acid will get rid of any anions that you don’t want.

49
Q

How can you test for halides for the solubility of these precipitates with Ammonia (NH3) dilute and concentrated?

A

AgCl dissolves in dilute and concentrated NH3.
AgBr dissolves in just concentrated NH3.
AgI dissolves in neither.

50
Q

Why does the litmus paper need to be damp when testing for ammonium compounds?

A

So the ammonia gas can dissolve into the paper and make the colour change.

A-level Chemistry Yr 12 Mine (15 decks)

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