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Chemistry > Group 7 > Flashcards

Group 7 Flashcards

1
Q

What is the trend in boiling points for the halogens?

A

Boiling points increase down the group due to the increasing strength of the van der Waals forces between the molecules.

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2
Q

What is the trend in electronegativity for the halogens?

A

Decreases down the group:
-Because as atoms get larger, the bonding pair of electrons in the covalent bond is further away and more shielded from the positive nucleus.

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3
Q

What is the trend in reactivity for the halogens?

A

When group 7 elements react, they gain an electron.
They get less reactive as you go down the group because the atom gets larger and there is more shielding. Therefore, the incoming electron is less attracted to the nucleus.

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4
Q

What is the trend in oxidising ability for the halogens?

A

a more reactive halogen will displace a less reactive halide. Oxidising ability decreases down the group.

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5
Q

What is the equation for the reaction between chlorine and cold, dilute, aqueous NaOH? what is this type of reaction called?
What is the observation?

A

Cl2(g) + 2NaOH(aq) → NaCl(aq) + NaClO(aq) + H2O(l)

  • Disproportionation reaction
  • Green gas to colourless solution
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6
Q

What is NaClO used for?

A
  • Bleach

- Disinfectant (kills bacteria)

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7
Q

What is the equation for the reaction between chlorine and water (not in the presence of sunlight)?

What happens to the equilibrium of this reaction as HClO kills microorganisms? What does this mean for the amount of Cl2 left?

A

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

the equilibrium shifts to the right, so very little Cl2 remains once the HClO has done its job.

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8
Q

What is the equation for the reaction between chlorine and water in the presence of sunlight?
Why does this happen?

A

Cl2(g) + H2O (l) ↔ 2HCl (aq) + 1/2 O2 (g)

UV radiation from the sun breaks down HClO into HCl and O2.

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9
Q

Why is the F-F bond weak?

A

F atoms are very small, so in a molecule of fluorine, the atoms are held so close together that the lone pairs of electrons in each atom repel each other, weakening the bond.

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10
Q

At room temperature, what do each of the halogens look like?

A
  • Fluorine is a pale yellow gas
  • Chlorine is a green gas
  • Bromine is a red-brown liquid
  • Iodine is a grey solid
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11
Q

What is the trend in atomic radius for the halogens?

A

As you go down the group, the atomic radius of the halogens increase, because each halogen will have one more electron shell compared to the one above it.

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12
Q

What is a displacement reaction?

A

A chemical reaction in which one atom or group of atoms replaces another in a compound.

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13
Q

Explain the trend in reducing ability of the halides.

A

Reducing ability increases as you go down the group. This is because as you go down the group, the ionic radii of the halides increase, so the outer electrons are further away and more shielded from the attraction of the nucleus. This means it’s easier for the outer electron to be removed.

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14
Q

What is the general equation for sodium halides reacting with concentrated sulfuric acid to give a hydrogen halide to begin with?

A

NaX + H2SO4 → HX + NaHSO4

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15
Q

What is the general equation for the reaction between a hydrogen halide and concentrated sulfuric acid, where the sulfuric acid is reduced further?

A

2HX + H2SO4 → SO2 + 2H2O + X2

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16
Q

What is the reaction between NaF or NaCl with concentrated H2SO4 and what are the observations?

Why is this not a redox reaction?
What type of reaction is this?

A

NaF (s) + H2SO4 (l) → HF (g) + NaHSO4 (s)
NaCl (s) + H2SO4 (l) → HCl (g) + NaHSO4 (s)

Misty fumes of HF/HCl produced as the gas comes into contact with moisture in the air.

It’s not a redox reaction because the oxidation states of both the sulfur and halide stay the same (+6 and -1)
It’s an acid-base reaction.

17
Q

What are the reactions between NaBr and concentrated H2SO4 and what are the observations?

What type of reactions are these?

A

NaBr (s) + H2SO4 (l) → HBr (g) + NaHSO4 (s)

2HBr (g) + H2SO4 (l) → SO2 (g) + 2H2O (l) + Br2 (g)

  • Misty fumes of HBr as gas comes into contact with moisture in the air.
  • Brown bromine gas.
  • Colourless, choking gas of SO2

-First reaction= acid-base
-Second = redox
Reactions are exothermic

18
Q

What are the reactions between NaI and concentrated H2SO4 and what are the observations?
What type of reaction is each one?

A

NaI (s) + H2SO4 (l) → HI (g) + NaHSO4 (s)
acid-base

2HI (g) + H2SO4 (l) → SO2 (g) + 2H2O (l) + I2 (g)
redox

6HI (g) + SO2 (g) → H2S (g) + 3I2 (s) + 2H2O (l)
redox

  • Misty fumes of HI
  • Rotten egg smell of H2S
  • Colourless SO2
  • Solid grey iodine (and maybe purple iodine vapour because the reaction is exothermic)
19
Q

What can the silver nitrate test be used for?

A

To identify and distinguish between halide ions.

20
Q

Describe how you would carry out the silver nitrate test for halide ions. What is the positive result for each of the halide ions?

what is the general ionic equation for the reaction that occurs?

A
  • Add dilute nitric acid to the sample in a test tube, which will get rid of ions which may interfere with the test by producing a precipitate (e.g. carbonate ions, sulfite ions)
  • Add a few drops of silver nitrate solution (AgNO3)

White precipitate= chloride ions
Cream precipitate= bromide ions
Yellow precipitate= iodide ions

Ag+ (aq) + X- (aq) → AgX (s), where X= Cl, Br or I

21
Q

When carrying out the silver nitrate test, why can’t you acidify the silver nitrate with hydrochloric acid?

A

Because the HCl contains chloride ions, so the nitrate ions will react with the chloride ions and give a white precipitate.

22
Q

Why does fluoride not produce a precipitate when acidified silver nitrate solution is added?

A

AgF is soluble in water.

23
Q

What happens to AgCl, AgBr and AgI when dilute and concentrated ammonia is added?

A

AgCl dissolves in dilute ammonia
AgBr dissolves in concentrated ammonia
AgI is insoluble in concentrated ammonia

24
Q

Which silver halide precipitate is the most soluble?

A

AgCl

25
Q

Which silver halide precipitate is the least soluble?

A

AgI

26
Q

what is the general trend in mean bond enthalpies of the halogens?
Which of the halogens does this trend apply to?

A

As you go down the group, bond enthalpies decrease generally.

  • Atomic radius and shielding increase, so the outer electrons are further away from and less attracted to the nucleus.
  • This is only true for chlorine, bromine and iodine, because fluorine has a weaker bond than expected.
27
Q

Why are fluorine and chlorine gases, whilst bromine is a liquid and iodine is a solid?

A

The boiling points of the halogens increase as you go down the group.

28
Q

After the silver nitrate test, why might ammonia solution be added?

A

To confirm the results/identity of the halide ions as all of the ppt. colours are quite similar.

29
Q

Why does AgCl dissolve in dilute ammonia?

A

A complex is formed. Ammonia molecules have a lone pair on the nitrogen which can form a coordinate bond with an unoccupied orbital of the silver ion. The complex ion is soluble, so the AgCl dissolves.

30
Q

Why might sodium fluoride and other fluorine containing compounds be added to water supplies?
Why are some people against it?

A

Fluoride ions can help prevent tooth decay as they strengthen enamel.
Some people are concerned because of health risks associated with fluoride.

31
Q

What are the formulas of the halate (I) ions?

A

Chlorate (I) = ClO-
Bromate (I) = BrO-
Iodate (I) = IO-

32
Q

Why is chlorine used in water treatment even though it’s toxic?

A

The benefits of using chlorine to treat water far outweighs the disadvantages (toxic effects)

33
Q

Why is chlorine used in water treatment?

A
  • Sterilises the water. Chlorate (I) ions kill bacteria and make the water safe to drink.
  • Prevents growth of algae, eliminating bad tastes and smells
  • Removes discolouration caused by organic compounds
34
Q

What are some disadvantages of using chlorine in water treatment?

A
  • Liquid chlorine on the skin and eyes causes severe chemical burns
  • Water contains various organic compounds (e.g. from decomposing plants). Chlorine can react with these compounds to produce chlorinated hydrocarbons (e.g. chloromethane) and many of these are carcinogenic.
35
Q

Why is concentrated sulphuric acid not commonly used to test for halide ions?

A

Sulfuric acid is corrosive, and toxic gases are formed in the reactions.

36
Q

Outline a test for ammonium ions.

A

Add sodium hydroxide solution to the sample, warm gently. If ammonium ions are present, then ammonia gas will be produced:

NH4+ (aq) + OH- (aq) → NH3 (g) + H2O (l)

Test the gas evolved using damp red litmus paper (it needs to be damp so NH3 can dissolve). The red litmus paper will turn blue because NH3 gas is alkaline.

37
Q

Iodide ions can reduce sulfuric acid to three different products. What are they?
What is the oxidation state of sulfur in each one?

A 
Sulfur dioxide (SO2) +4
Hydrogen sulfide (H2S) -2
Sulfur (S) 0
38
Q

During the reduction of sulfur from +6 to -2, why might a yellow solid be observed?

A

Solid sulfur may be produced.

Chemistry (14 decks)

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