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CloudLearn A-level Chemistry > Group 7 > Flashcards

Group 7 Flashcards

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1
Q

How does fluorine exist at room temperature?

A

Yellow Gas

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2
Q

How does chlorine exist at room temperature?

A

Green Gas

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3
Q

Which element in Group 7 exists as a yellow gas at room temperature?

A

Fluorine

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4
Q

Which element in Group 7 exists as a green gas at room temperature?

A

Chlorine

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5
Q

How does bromine exist at room temperature?

A

Brown liquid

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6
Q

Which element in Group 7 exists as a brown liquid at room temperature?

A

Bromine

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7
Q

How does iodine exist at room temperature?

A

Purple solid

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8
Q

Which element in Group 7 exists as a purple solid at room temperature?

A

Iodine

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9
Q

Which Group 7 element doesn’t exist as a diatomic molecule?

A

Astatine

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10
Q

What’s the trend in volatility down Group 7 and how can you tell?

A

Decreasing volatility going down group 7, as evidenced by the different physical states of each element, from gaseous Fluorine and Chlorine to liquid Bromine to solid Iodine and Astatine.

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11
Q

What’s the trend in solubility going down Group 7?

A

Decreasing solubility in water going down Group 7, this is closely related to the decrease in oxidising strength.

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12
Q

Which Group 7 element isn’t experimented with outside of professional lab conditions and why?

A

Fluorine is a strong oxidising agent, which reacts violently with water to produce hydrogen fluoride, oxygen and ozone gas mixtures; and so fluorine is not normally experimented with outside of professional laboratory conditions

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13
Q

Do Group 7 elements have a strong affinity to bond with water molecules?

A

Yes

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14
Q

Describe & explain the trend in m.p. & b.p. down Group 7

A

We know that going down the halogen group there is an increase in proton and electron contents as well as atomic radius. The bigger the molecules, the more electrons there are that can move around them to create temporary dipoles that lead to the van der Waals forces. The stronger the intermolecular forces, the more heat energy is needed to break these bonds, so the melting and boiling points will also increase.

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15
Q

What’s the rule for the displacement of halogens?

A

The more reactive halogens can also displace the less reactive halide ions

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16
Q

What’s the observation when Cl2 is added to KCl solution?

A

No colour change (no reaction)

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17
Q

What colour is Cl2, Br2 & I2 in the displacement reactions?

A

Colourless, orange & brown respectively

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18
Q

What colour is KCl, KBr & KI in the displacement reactions?

A

All colourless

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19
Q

What’s the observation when Cl2 is added to KBr solution?

A

Orange solution (Br2 produced)

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20
Q

What’s the observation when Cl2 is added to KI solution?

A

Brown solution (I2 produced)

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21
Q

What’s the observation when Br2 is added to KCl solution?

A

No colour change (no reaction)

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22
Q

What’s the observation when Br2 is added to KBr solution?

A

No colour change (no reaction)

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23
Q

What’s the observation when Br2 is added to KI solution?

A

Brown solution (I2 produced)

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24
Q

What’s the observation when I2 is added to KI solution?

A

No colour change (no reaction)

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25
Q

What’s the observation when I2 is added to KCl solution?

A

No colour change (no reaction)

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26
Q

What’s the observation when I2 is added to KBr solution?

A

No colour change (no reaction)

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27
Q

What observation can be applied to all the displacement reactions between Group 7 elements & compounds

A

Generally, the more reactive halogen will replace the less reactive halide and produce the less reactive halogen in the process

28
Q

When Cl2 reacts with each potassium halide when are colour changes observed and why?

A

When Chlorine is added to each potassium halide, colour changes are observed in Potassium Bromide and Potassium Iodide, but not in Potassium Chloride. This is because Chlorine is the most reactive halogen and is able to displace bromide and iodide

29
Q

Give the ionic equation for the reaction between a halogen (Y) and potassium halide (KX) when a displacement reaction does occur

A

Y2 (aq) + 2X- (aq) -> 2Y- (aq) + X2 (aq)

30
Q

When Br2 reacts with each potassium halide when are colour changes observed and why?

A

When Bromine is added to each potassium halide, a colour change is observed in Potassium Iodide, but not in Potassium Bromide or Potassium Chloride. This is because Bromine is only more reactive compared to Iodine, not Chlorine or itself

31
Q

When I2 reacts with each potassium halide when are colour changes observed and why?

A

When Iodine is added to each potassium halide, NO colour change is observed because Iodine is the least reactive halogen and is therefore not capable of displacing either chloride, bromide or even iodide.

32
Q

What 2 tests can prove the trend in reducing power of halide ions?

A

Reacting halide ions with sulphuric acid or with silver nitrate

33
Q

In the test for reducing strength of a halide using sulphuric acid, what are the products?

A
  1. An acid with the halide ion (e.g. HCl)
  2. A hydrogen-sulphate ion (HSO4^-)
  3. SO2 for Br- & I-
  4. H2O for Br- & I-
  5. Halogen for Br- & I-
  6. Sulphur for I-
  7. H2S for I-
34
Q

What happens to hydrogen halides when in contact with moisture?

A

They produce steamy fumes

35
Q

Give the equation for when sulphuric acid is used to test for a halide ion (X-). For which halides does this reaction occur?

A
  • X- + H2SO4 -> HX + HSO4^-
  • Cl-, Br- and I-
36
Q

Which halide ions do and don’t do further oxidation in the test for halide ions using H2SO4 and what’s the product when further oxidation happens here?

A
  • Cl- doesn’t because it isn’t a strong enough reducing agent. Br- & I- does
  • SO2
37
Q

Give the half equations & the full ionic equation for when further oxidation occurs in the halide (X-) tests for reducing power using H2SO4. For which halides does this reaction occur?

A
  1. 2X- -> X2 + 2e-
  2. H2SO4 + 2H+ + 2e- -> SO2 + 2H2O
    Overall: H2SO4 + 2H+ + 2Br- -> Br2 + SO2 + 2H2O
    - Br- and I-
38
Q

Which is halide ion does the furthest oxidation in the test for halide ions using H2SO4 and what are the products when further oxidation happens here?

A

Iodide goes the furthest to produce two additional products, Sulphur and Hydrogen Sulphide

39
Q

Give the half equations & the full ionic equations for the only halide to do the furthest oxidation in the halide tests for reducing power using H2SO4

A
  • Reducing for Sulphur:
    1. 6I- -> 3I2 + 6e-
    2. H2SO4 + 6H+ + 6e- -> S + 4H2O
    Overall. H2SO4 + 6H+ + 6I- -> 3I2 + S + 4H2O
  • Reducing for H2S:
    1. 8I- -> 4I2 + 8e-
    2. H2SO4 + 8H+ + 8e- -> H2S + 4H2O
    Overall. H2SO4 + 8H+ + 8I- -> 4I2 + H2S + 4H2O
40
Q

Give the observations & why they came about for when Cl- is used in the reducing power of halides test using H2SO4

A

Steamy fumes from HCl production

41
Q

In the halide tests for reducing power using H2SO4, which halide gives the observations:
- steamy fumes

A

Cl-

42
Q

Give the observations & why they came about for when Br- is used in the reducing power of halides test using H2SO4

A
  • Steamy fumes from HBr production
  • Orange vapour from Br2
43
Q

In the halide tests for reducing power using H2SO4, which halide gives the observations:
- steamy fumes
- orange vapour

A

Br-

44
Q

Give the observations & why they came about for when I- is used in the reducing power of halides test using H2SO4

A
  • Steamy fumes from HI production
  • Yellow solid from S
  • Rotten egg smell from H2S
45
Q

In the halide tests for reducing power using H2SO4, which halide gives the observations:
- Steamy fumes from HI production
- Yellow solid from S
- Rotten egg smell from H2S

A

I-

46
Q

Describe & explain the test for the presence of halides

A

The test for the presence of halides essentially uses Silver Nitrate (AgNO3) followed by ammonia (NH3) solution. The general protocol is:
1. Add dilute nitric acid (HNO3) to a halide solution (Cl-, Br - or I-) to remove any other anions such as carbonates because they could give false positive results
2. Add AgNO3 to the solution and look for the development of colour due to halide precipitates to identify the halide:
- Silver Chloride is a white precipitate
- Silver Bromide is a cream precipitate
- Silver Iodide is a yellow precipitate
3. Further confirmation test with NH3 as follows:
- For Cl-, AgCl white precipitate dissolves in dilute NH3
- For Br-, AgBr cream precipitate dissolves in concentrated NH3 .
For I-, AgI yellow precipitate is insoluble in concentrated NH3.

47
Q

When is the Silver Nitrate test used on solutions?

A

When testing for the presence of halide

48
Q

Give the ionic equation for when the Silver Nitrate test happens on halides (X-)

A

X- (aq) + Ag+ (aq) -> AgX (s)

49
Q

When is ammonia added after the Silver Nitrate test on solutions?

A

When achieving further confirmation of presence of halide

50
Q

Explain Fluorine’s usefulness

A

Fluorine’s too volatile to be useful

51
Q

State some of Chlorine’s uses

A
  • Water sterilisation for drinking water and swimming pool
  • In bleach for cleaning products
52
Q

Which halogen is used in water sterilisation?

A

Chlorine

53
Q

Which halogen is used in cleaning products?

A

Chlorine

54
Q

Describe & explain the use of a halogen in water sterilisation. Include redox equations if needed.

A
  • Adding Chlorine to water will sterilise it by producing chlorate ions (ClO-) which will be able to kill microorganisms (including cholera bacteria) by oxidising them
  • It can also be used for treatment over a longer period of time, for example, it can prevent the build-up of bacteria and the growth of algae that discolours the water and creates a bad odour
  • The mixing will produce chlorate (I) ions (ClO- ):
    Cl2 (g) + H2O (l) -> 2H+ (aq) + Cl- (aq) + ClO- (aq)
  • The oxidation state of:
    1. Cl2 is 0
    2. Cl- is -1
    3. ClO- is +1
  • The oxidation states of -1 and +1 in the products show that the element Chlorine has actually been oxidised and reduced simultaneously in this reaction. This type of reaction is called the disproportionation reaction.
  • Chlorate (I) solution can be used to sterilise drinking water and swimming pool water. However, in the presence of sunlight, chlorinated water can decompose via the following reaction:
    2H2O (l) + Cl2 (g) + sunlight -> 4H+ (aq) + 2Cl- (aq) + O2 (g)
  • Here, no chlorate (I) ions are produced, and therefore the water is no longer sterile. This is why swimming pool water chlorination has to be done regularly to maintain sterility.
55
Q

State some risks of using the halogen in water sterilisation. Why do we use it anyway?

A

We know that chlorine gas is actually quite toxic and can be an irritant on the respiratory system. Liquid chlorine, on the other hand, can cause severe chemical burns on the skin. Furthermore, chlorine has also been shown to react with organic compounds in the water to make chloroalkanes, which have been linked to cancer. However, all of these risks are quite minimal as the concentrations used are low and the need to chlorinate water to prevent an epidemic, such as cholera, is more pressing.

56
Q

Describe & explain the use of a halogen in cleaning products. Include redox equations if needed.

A
  • Bleach is made by mixing chlorine and sodium hydroxide (NaOH) to produce sodium chlorate (I) (NaClO) as in the following equation:
    2NaOH (aq) + Cl2 (g) -> NaClO (aq) + NaCl (aq) + H2O (l)
  • The oxidation state of:
    1. Cl2 is 0
    2. Chlorine in NaClO is +1
    3. Chlorine in NaCl is -1
  • This is a disproportionation reaction as chlorine is getting oxidised and reduced at the same time.
  • As we know, bleach can be used as a cleaning product, but it can also be used to treat water, paper and fabric during processing.
  • It has to be noted that bleach is made using the mixture of Chlorine and cold, dilute and aqueous NaOH. If a hot NaOH is used instead, the reaction will produce a sodium penta-chlorate or sodium (V) chlorate (NaClO 3) as shown in the equation below:
    6NaOH + 3Cl2 -> 5NaCl + NaClO3 + 3H2O
57
Q

Describe & explain the test for Group 2 ions in a solid compound

A
  • This can be done by the flame test
    1. Group 2 metals can be dissolved into a solution for this test
    2. Dip a nichrome wire loop in concentrated hydrochloric acid to clean it
    3. Dip into the sample solution
    4. Place the loop into the blue part of a Bunsen flame and observe the colour produced:
  • If it is brick red, it is Calcium ion (Ca2+).
  • If it is bright red, it is Strontium ion (Sr2+).
  • If it is pale green, it is Barium ion (Ba2+)
  • If a bright white light is produced, it is Magnesium ion (Mg2+). Note that this isn’t classed as a flame colour
58
Q

Describe & explain the test for the presence of NH4 in a compound

A
  • For testing NH4 compounds:
    1. Add NaOH to the compound
    2. Gently heat and observe
    3. If ammonia (NH3) gas is produced then ammonium (NH4) must have been present
    4. Use a damp red litmus paper to test as ammonia will turn litmus paper blue.
  • The chemical equation is as follows:
    NH4+ (aq) -> NH3 (g) + H2O (l)
59
Q

Describe & explain the test for the presence of hydroxide compounds in a solution

A
  • For testing hydroxide compounds:
    1. Use a damp red litmus paper and dip into a solution of the unknown compound.
    2. The red litmus paper will turn blue if hydroxides are present.
  • However, the litmus test can only tell you if a compound is acidic or alkaline. Further tests are needed to confirm if it is a hydroxide.
60
Q

Describe & explain the test for the presence of carbonates in a compound

A
  • Test for carbonates (CO3^2–) by:
    1. Adding hydrochloric acid to the carbonate compound, wherein carbon dioxide gas is produced and if bubbled through some lime water (Ca(OH)2), it turns the lime water cloudy from white Ca(OH)2 precipitate produced
  • The chemical equations for the test:
    1. Na2CO3 (s) + HCl (aq) -> NaHCO3 (aq) + NaCl (aq)
    2. NaHCO3 (aq) + HCl (aq) -> NaCl (aq) + H2O (l) + CO2 (g)
    Overall. CO3^2- (aq) + 2H+ (aq) -> CO2 (g) + H2O (l)
  • This is the equation for CO2 turning limewater cloudy: CO2(g) + Ca(OH)2 (aq) limewater -> CaCO3 (s) + H2O (l)
61
Q

Describe & explain the test for the presence of sulphates in a compound

A
  • Test for sulphates (SO42-) can be done by:
    1. First adding hydrochloric acid into the compound solution to remove carbonates, which might lead to false positive results.
    2. This is followed by the addition of Barium Chloride (BaCl)
  • If sulphate is present in the compound then a white, insoluble Barium Sulphate (BaSO4) precipitate will be produced
  • The chemical equation for the test:
    Ba^2+ (aq) + SO4^2- (aq) -> BaSO4 (s)
62
Q

Would it be better to use ozone, rather than halogen, to purify water? Why or why not?

A

No - it’s less toxic than chlorine but more expensive and evaporates from water more quickly

63
Q

What is desalination? What are the advantages and disadvantages of this?

A
  • Converts saltwater into clean, potable water either by reverse osmosis (using a smart membrane) or by vacuum distillation at low pressure and low temperature
  • Advantages - safe, clean, drinkable water produced in places where it might not otherwise be available
  • Disadvantages - uses lots of energy, reverse osmosis has low efficiency, can disturb marine ecosystems
64
Q

Concentrated sulfuric acid reacts with solid sodium chloride. Give the observation you would make in this reaction. State the role of the sulfuric acid

A
  • Observation with sodium chloride: White/misty/steamy fumes
  • Role of sulfuric acid: acid/proton donor
65
Q

Concentrated sulfuric acid reacts with solid sodium iodide, to produce several
products. Observations made during this reaction include the formation of a black solid, a yellow solid and a gas with the smell of bad eggs. Identify the product responsible for each observation

A
  • Black solid: iodine
  • Yellow solid: sulfur
  • Gas: hydrogen sulfide
66
Q

Which shows the major product(s) formed when chlorine reacts with
cold, dilute, aqueous sodium hydroxide?

A. NaCl only
B. NaClO only
C. NaCl and NaClO
D. NaCl and NaClO3

A

NaCl and NaClO

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