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OCR A-Level Chemistry Henry K > Chapter 8 - Reactivity Trends > Flashcards

Chapter 8 - Reactivity Trends Flashcards

Group 2, The halogens and Quantitative analysis.

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1
Q

What is a reducing agent?

A

A species that donates it’s electrons to another species, thereby reducing that species.

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2
Q

Which group are reducing agents commonly found?

A

Group 2

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3
Q

What is the trend in reactivity down group 2?

A

Reactivity increases.

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4
Q

Explain the trend of reactivity down group 2

A

There is increased atomic radius and shielding effect, therefore ionisation energies decrease. Therefore it’s easier to lose electrons as the attraction between the nucleus and the outer electrons decrease.

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5
Q

What are the products of a group 2 element reacting with water?

A

Metal hydroxide and hydrogen

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6
Q

What is the product of a group 2 element reacting with oxygen?

A

Metal oxide

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7
Q

What is the trend of solubility down group 2?

A

Increases

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8
Q

Explain the trend of solubility down group 2

A

as you go down the group, the solution has a greater concentration of OH-.
hence solubility increases

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9
Q

Given that group 2 oxides, hydroxides and carbonates neutralise acids, what can they be referred to as?

A

Bases

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10
Q

Given that most group 2 oxides, hydroxides and carbonates are soluble in water, what are they also besides bases?

A

Alkalis

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11
Q

What is the use of calcium hydroxide in agriculture?

A

Increases the pH of acidic soils.

Ca(OH)(2) + 2H+ -> Ca2+ + 2H(2)O

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12
Q

How are group 2 compounds used in medicine?

A

Used in indigestion tablets as antacids

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13
Q

What is another name for group 2?

A

Alkaline Earth Metals

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14
Q

What is another name for group 7?

A

Halogens

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15
Q

What is the trend in boiling point down group 7?

A

Increases

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16
Q

Explain the trend in boiling point down group 7

A

More electrons,
Stronger London forces,
More energy to break intermolecular forces,
Boiling point increases.

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17
Q

What is the trend in reactivity down group 7?

A

Reactivity decreases

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18
Q

Explain the trend in reactivity down group 7

A
  • Atomic radius increases,
  • More inner shells,
  • Shielding increases,
  • Nuclear attraction decreases, harder to capture e- from another species.
  • Reactivity decreases
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19
Q

What do more reactive halogens do to less reactive halide ions?

A

Displace them

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20
Q

What can displacement reactions be used to identify?

A

Which halide is present in solution.

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21
Q

Which compound is used to test for halides?

A

Silver nitrate solution

22
Q

How can the results for a halide test be further tested?

A

Solubility in ammonia solution

23
Q

What is disproportionation?

A

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

24
Q

Describe the test for carbonates

A
  • Add unknown compound into test tube and add nitric acid to test tube
  • Bubbling indicates carbonate might be present, so CO2 gas will be released.
  • Bubble the CO2 gas in limewater, Ca(OH)2, which will turn form a milky white ppt.
  • Confirming presence of carbonate.
25
Q

Describe the test for sulfates

A

Aqueous barium ions are added to the solution. If a white precipitate forms, there is a sulfate.

26
Q

In the halide tests, what happens to chloride with silver nitrate and then ammonia

A

Silver nitrate - white precipitate

Ammonia - soluble in dilute ammonia

27
Q

In the halide tests, what happens to bromide with silver nitrate and then ammonia

A

Silver nitrate - cream precipitate

Ammonia - soluble in concentrated ammonia

28
Q

In the halide tests, what happens to iodide with silver nitrate and then ammonia

A

Silver nitrate - yellow precipitate

Ammonia - insoluble in concentrated ammonia

29
Q

What is the correct order for these anion tests?

A

Carbonate test, sulphate test, halide test

30
Q

Why is this the correct order for anion tests carbonate, sulphate, halide?

A

Carbonates also form a white
precipitate in the sulphate test such as barium carbonate but not vice versa. So first must rule out there isn’t any carbonates present
Carbonates and sulphates form precipitates with silver nitrate. Such as Ag2CO3 and Ag2SO4.

31
Q

Describe the test for ammonium ions

A
  • Add source of hydroxide ions to solution to be tested, such as NaOH
  • If Ammonium ion (NH4+) is present, it’ll react with OH-(hydroxide ion) to produce Ammonia gas (NH3) and liquid water (H20)
  • Heat test tube to release ammonia gas, as initially, the NH3 gas is soluble in H20.
  • When gas released, you may smell it, but it’s easier to test with red litmus paper.
  • Where presence of Alkaline ammonia will turn paper from red to blue.
32
Q

If I want to work out which halide is present in a solution what can I do

A

Run a displacement reaction

33
Q

A Cl2 is added to a Br- ion. What observation will you see with and without the organic non-polar solvent cyclohexane present

A

Orange colour will form as the chlorine would have displaced the bromide ion

With cyclohexane - you will see a orange colour

34
Q

A Cl2 is added to a I- ion. What observation will you see with and without the non-polar cyclohexane

A

Brown colour change as the chlorine would have displaced the Iodine ion

In cyclohexane - it is violet colour

35
Q

A Br2 is added to a I- ion. What observation will you see with and without the non-polar,organic solvent, cyclohexane?

A

Brown colour change as the halogen would have displaced the Iodine ion

In cyclohexane- it would be a violet colour change

36
Q

What colour is Cl2 in water

A

Pale green

37
Q

What colour is fluorine

A

Pale yellow

38
Q

Describe the astatine

A

Rare, radioactive and decays rapidly

Least reactive halogen

39
Q

What groups are the best oxidising event and describe the oxidising trend as you go down the group

A

Halogens

As you go down the group the halogens become weaker oxidising agents

40
Q

Which compounds neutralises stomach acid

A

Magnesium hydroxide

Calcium carbonate

41
Q

At RTP describe chlorine, bromine and iodine

A

Chlorine is a pale green gas
Bromine is liquid, extremely toxic, and vaporises readily
Iodine is a solid with grey-black crystals

42
Q

Show the reaction of chlorine with water and what kind of reaction is this

A

Cl2(aq) + H20(l)&raquo_space;> HCLO(aq) + HCL(aq)

Disproportionation reaction

43
Q

Show the reaction of chlorine with cold, dilute aqueous sodium hydroxide and what kind of reaction is this

A

Cl2(aq) + 2NaOH(aq)&raquo_space;> NaCLO(aq) + NaCl(aq) + H20(l)

  • Disproportionation reaction
  • Resulting solution contains a large conc of chlorate(I), ClO-, ions from the sodium chlorate,NaClO, that’s formed.
44
Q

What do household bleach contain

A

Sodium chlorate (I), NaClO made by reacting chlorine with sodium hydroxide

45
Q

Benefits and risk of chlorine use

A

Disinfectant for water
Ensure no disease breakout

Respiratory irritant
Cause cancer b/ of the formation of chlorinated hydrocarbons

46
Q

Explain the test that would be carried out on a mixture of ions

A

1) Carbonate test:

If you see bubbles, continue adding dilute nitric acid until the effervescence stops

All carbonate ion will then have been removed and there will be none left to react in the next tests. We don’t use sulfuric acid or hydrochloric acid because it contains sulfate and chloride ions , which will show
up in the sulfate and halide test

2) Sulfate test:

Add an excess of Ba(NO3)2
Any sulfate ion present will precipitate out as barium sulfate
Filter the solution to remove the barium sulfate

3) Halide test:

For the solution left, add AgNO3 (aq)
Any carbonate or sulfate ion present have already been removed. Therefore any PPT must involve halide ions.

Add NH3 to confirm which halide you have

47
Q

what are the main ingredients for antacids

A

calcium carbonates and magnesium hydroxide

48
Q

what is the purpose of adding the organic solvent, cyclohexane to halogen

A

to see a better colour change as the halogens are more soluble

49
Q

How could you distinguish between NaCl, NaBr, and NaI by a simple test?

A 
Add AgNO3(aq) to an aqeuous solution of each
- If Cl- ions are present, a white PPT will form which disolves in dilute NH3(aq)
  • If Br- ions are present, a cream PPT will form which dissolves in conc NH3(aq)
  • If I- ions are present, a yellow PPT will form which is insoluble in conc NH3(aq)
50
Q

Explain why it is important to carry out the carbonate test before carrying out a sulfate test on an unknown chemical?

A

Dilute nitric acid reacts with carbonate ions and no precipitate of barium carbonate will then form

51
Q

Explain why, if you are testing a mixture, it is important to use dilute nitric acid, rather than sulfuric or hydrochloric acid, for the carbonate test?

A
  • If sulfuric acid is used, sulfate ions are added and will show up in the sulfate test with Ba2+(aq).
  • If hydrochloric acid is used, chloride ions are added and will show up in the halide test with Ag+(aq).

OCR A-Level Chemistry Henry K (35 decks)

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