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A-level AQA Chemistry > Inorganic: Group 7 Halogens > Flashcards

Inorganic: Group 7 Halogens Flashcards

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1
Q

What colour and state is fluorine at room temperature?

A

pale yellow gas

very reactive

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2
Q

What colour and state is chlorine at room temperature?

A

greenish, reactive gas

poisonous at high concentrations

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3
Q

What colour and state is bromine at room temperature?

A

red liquid

gives off dense brown/orange poisonous fumes

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4
Q

What colour and state is iodine at room temperature?

A

shiny grey solid

(sublimes to purple gas)

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5
Q

What is the trend for mp/bp?

A

increases down the group

  • molecules become larger and they have more electrons so have larger van der Waals forces between mol.
  • IMF become stronger so more energy is required to break the forces
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6
Q

What is the trend for electronegativity?

A

electronegativity decreases
as you go down the group, atomic radii increases due to the increasing number of shells, (more inner shielding electrons) so it is less able to attract the bonding pair of electrons

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7
Q

What is electronegativity?

A

the relative tendency of an atom in a molecule to attract pairs of electrons in a covalent bond

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8
Q

How do displacement reactions with halogens work?

A

a halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power from one of its compounds

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9
Q

How does oxidising strength increase change in group 7?

A

oxidising strength decreases down the group

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10
Q

What are oxidising agents/reducing agents?

A

oxidising agents- electron acceptors

reducing agents- electron donors

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11
Q

What will be the observations of displacement reactions of halide ions by halogens?

A

the colour of the solution in the test tube shows which free halogen is present in the test
chlorine- pale green solution
bromine- yellow solution
iodine- brown solution (sometimes a black solid is present)

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12
Q

What is the test used to identify halide ions?

A

reaction of sample with silver nitrate

add nitric acid, then silver nitrate dropwise

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13
Q

Why is nitric acid added in the test to identify halide ions?

A

the nitric acid will react with carbonates to prevent formation of carbonates, which would mask desired observations

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14
Q

What are the results of the nitric acid test to identify reactions of halide ions?

A

fluorides- no precipitates
chlorides- white precipitate
bromides- cream precipitate
iodides- pale yellow precipitate

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15
Q

What can be used to differentiate between similar colours of silver halides?

A

ammonia solution
silver chloride dissolves in DILUTE ammonia (colourless)
silver bromide dissolves in CONCENTRATED ammonia
silver iodide does not react with ammonia, it is too insoluble

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16
Q

What is the trend in reducing agents down the group and how can this be shown?

A

halides show increasing power as reducing agents down the group, can be shown in the reactions of solid halides with concentrated sulfuric acid

17
Q

Why does reducing power increase down the group?

A

because ions get bigger, more shells, further distance

weaker nuclear attraction, easier to give outer electrons away

18
Q

What happens when you react fluoride and chloride with concentrated sulfuric acid?

A

F- and Cl- are not strong enough reducing agents to reduce the S in H2SO4 so no redox reactions occur, only acid-base reactions occur

19
Q

What are the results of NaF with concentrated sulfuric acid?

A

white steamy fumes of HF are evolved

NaF (s) + H₂SO₄(l) —> NaHSO₄ (s) + HF (g)

20
Q

What are the results of NaCl with concentrated sulfuric acid?

A

white steamy fumes of HCl are evolved

NaCl (s) + H₂SO₄(l) —> NaHSO₄ (s) + HCl (g)

21
Q

What happens to NaBr with concentrated sulfuric acid?

A

after initial acid-base reaction, it reduces the S in H₂SO₄ from +6 to +4 in SO₂ (because it is a stronger reducing agent)
Observations: white steamy fumes of HBr evolved
orange fumes of bromine and a colourless acidic gas

22
Q

What is the reduction product of NaBr reaction with concentrated sulfuric acid?

A

sulfur dioxide

23
Q

What are the formulae for the reaction of bromide ions with concentrated sulfuric acid?

A

acid-base: NaBr(s) + H₂SO₄(l) —> NaHSO₄ (s) + HBr (g)

redox: 2HBr + H₂SO₄ —> Br₂(g) + SO₂(g) + 2H₂O (l)

24
Q

What role does H₂SO₄ play in its reaction with sodium bromide?

A

it plays the role of the acid in the first step producing HBr and then acts as an oxidising agent in the 2nd redox step

25
Q

What are the observations of NaBr reacting with concentrated sulfuric acid?

A
  • white steamy fumes of HI are evolved
  • black solid and purple fumes of iodine are evolved too
  • colourless acidic gas SO₂
  • yellow solid of sulfur
  • H₂S (hydrogen sulfide) a gas with a bad egg smell
26
Q

What are the formulae for the reaction of NaBr with concentrated sulfuric acid?

A

NaI(s) + H₂SO₄ (l) —> NaHSO₄(s) + HI(g)
2HI + H₂SO₄ —-> I₂(s) + SO₂(g) + 2H₂O(l)
6HI + H₂SO₄ —-> 3I₂(s) + S(s) + 4H₂O (l)
8HI + H₂SO₄ —-> 4I₂(s) + H₂S (g) + 4H₂O (l)

27
Q

What is the reduction product for the reaction of NaBr with concentrated sulfuric acid?

A

sulfur dioxide, sulfur and hydrogen sulfide

28
Q

What role does H₂SO₄ play in its reaction with NaBr?

A

plays the role of acid (in the first step, producing HI)

then acts as an oxidising agent in the 3 redox steps

29
Q

What is a disproportionation reaction?

A

a reaction where the same element simultaneously oxidises and reduces

30
Q

What is the formula of the reaction between chlorine and water?

A

Cl₂(g) + H₂O(l) ⇌ HClO (aq) + HCl (aq)

chlorine is both simultaneously reducing and oxidising

31
Q

What observations could be made if you add universal indicator to the reaction of chlorine with water?

A

it will first turn red due to acidity of both reaction products, then it will turn colourless as the HClO bleaches the colour

32
Q

What is the reaction of chlorine and water in bright sunlight?

A

2Cl₂ + 2H₂O —-> 4H+ +4Cl- + O₂

greenish colour of chlorine water fades as the Cl₂ reacts and a colourless gas O₂ is produced

33
Q

Why are swimming pools treated with chlorine?

A

to kill bacteria

used to treat drinking water as well (benefits of this outweighs its toxic effects)

34
Q

What is the reaction of chlorine with cold dilute NaOH solutions?

A

Chlorine and other halides will react
Cl₂ (aq) + 2NaOH (aq) —> NaCl (aq) + NaClO (aq) + H₂O (l)
mixture of NaCl and NaClO is used as bleach to disinfect/kill bacteria

35
Q

What is the IUPAC name for NaClO and NaClO₃?

A 
sodium chlorate (I)
sodium chlorate (V)
36
Q

What is the IUPAC name for K₂SO₄ and K₂SO₃?

A 
potassium sulfate (VI)
potassium sulfate (IV)

A-level AQA Chemistry (9 decks)

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