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Inorganic Chemistry Year 12 > 3.1.3 Halogens > Flashcards

3.1.3 Halogens Flashcards

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1
Q

outline the basics of halogens

A
  • group 17
  • most reactive non-metallic group
  • halogen = element VS halide = ion (how they are naturally found, or in compounds)
  • at RTP, exist as diatomic molecules
  • as solids, form lattices with simple molecular structure
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2
Q

how does F2 appear

A

pale yellow gas

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3
Q

how does Cl2 appear

A

pale green gas

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4
Q

how does Br2 appear

A
  • red-brown liquid
  • orange vapour
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5
Q

how does I2 appear

A
  • shiney grey-black solid
  • purple vapour
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6
Q

how does At2 appear

A

never been seen

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7
Q

what is the trend in boiling points down the halogens

A

INCREASES down group
(why F2 is a gas and I2 is a solid at room temperature)

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8
Q

explain the trend in boiling points in halogens as you go down the group

A

1) more electrons
2) stronger London dispersion forces
3) more energy required to break the IMFs
4) boiling point INCREASES

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9
Q

what is the most common reaction of group 17

A

redox reactions

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10
Q

how do halogens undergo redox reactions

A
  • have 7 electrons in outer shell (2 in outer s sub-shell and 5 in p sub-shell, s2p5)
  • the halogen is REDUCED:
  • gains 1 e-
  • forms 1- ion
  • Cl2 + 2e- ===> 2Cl-
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11
Q

why are halogens referred to as oxidising agents

A
  • cause other species to lose electrons to the halogen atoms
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12
Q

what displacement reaction can be used to show the relative reactivities of group 7 elements

A

halogen-halide displacement reactions
- can happen on a test-tube scale

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13
Q

explain the displacement reactions of halogen-halides

A

1) add a solution of halogen
2) to an aqueous solutions of other halide ions
3) if halogen is more reactive than halide present
- reaction takes place and halogen displaces halide out of solution
- the solution changes colour to least reactive halide

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14
Q

what colour are the solutions of halogens in water

A

Cl2 = pale green
Br2 = orange
I2 = brown

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15
Q

what is the problem of using halogen solutions in water to test for displacement

A

solutions of iodine and bromine in water can appear a similar orange-brown shade, so not good for noticing a colour change

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16
Q

which solutions of halogens do you actually use when carrying out displacement reactions

A
  • add a organic, non-polar solvent to mixture and shake to tell apart
  • in CYCLOHEXANE:
  • Cl2 = pale green
  • Br2 = orange
  • I2 = VIOLET
17
Q

write the equation and colour change for chlorine added to bromide ions

A

Cl2(aq) + 2Br-(aq) ===> Br2(aq) + 2CL- (aq)

  • from pale green to orange (Br2)
18
Q

write the equation and colour change for adding chlorine to iodide ions

A

Cl2(aq) + 2I- ===> 2Cl-(aq) + I2(aq)

  • from pale green to violet (I2)
19
Q

write the equation and colour change for adding bromine to iodide ions

A

Br2(aq) + 2I-(aq) ===> 2Br-(aq) + I2(aq)

  • from orange to violet (I2)
20
Q

explain the redox reaction taking place in displacement of halogens and halides, including oxidation numbers

A

HALOGEN : 0 to -1 (reduced)
HALIDE : -1 to 0 (oxidised)

  • total increase and decrease by 2 (as 2 atoms present)
21
Q

explain why F2 and At2 aren’t included in the halide-halogen displacement reactions

A

F2: pale yellow gas, which is VERY REACTIVE and reacts with almost everything
At2: very rare as radioactive so decays very fast, never actually seen but assumed to be the least reactive

22
Q

what is the trend of reactivity down group 7

A

DECREASES:
- redox occurs by halogens GAINING an e-, and down the group, the tendency for them to do this decreases
- become weaker oxidising agents down the group

23
Q

explain the trend of reactivity down group 7

A

1) atomic radius increases
2) more inner shells, so shielding increases
3) increase in nuclear charge, but this is outweighed by other factors
4) less nuclear attraction to capture e- from other species
5) so reactivity DECREASES

24
Q

what is disproportionation

A

a redox reaction where the same element is both oxidised and reduced

25
Q

what are 2 examples of disproportionation

A

chlorine + water
chlorine + cold, dilute sodium hydroxide

26
Q

why is chlorine used in water

A

used to kill bacteria, as a disinfectant to keep water sterile for swimming and drinking

  • the hydrogen chlorate (I) / chloric acid produced, along with the chlorate ions ClO-, are the component which kills the bacteria
  • can also act as a weak bleach (if you add indicator, it will turn red, due to presence of two acids, but the colour will soon disappear as the bleaching properties appear)
27
Q

write the redox reaction for chlorine + water

A

Cl2(aq) + H2O(l) ===> HClO(aq) + HCl(aq)

CL2= 0
HClO = +1 (oxidised)
HCl = -1 (reduced)

28
Q

explain the reaction of chlorine and cold, dilute sodium hydroxide

A
  • much more chlorine will dissolve, as was limited in water
  • used in household bleach, which contains large concentrations of ClO- ions
29
Q

write down the equation of chlorine and cold, dilute sodium hydroxide

A

Cl2(aq) + 2NaOH(aq) ===> NaClO + NaCl + H2O(l)

Cl2= 0
NaClO = +1 (oxidised)
NaCl = -1 (reduced)

30
Q

what are the benefits of using chlorine in water treatment

A

kills bacteria so water is sterile and safe to drink

31
Q

what are the risks of using chlorine in water treatment

A
  • chlorine is toxic
  • if mixed with hydrocarbons (e.g. methane produced by decaying vegetation), can form chlorinated hydrocarbons which are potential carcinogens
32
Q

why is chlorine still used in water treatment despite the drawbacks

A

the benefits outweigh the risks (may cause breakout of disease is water is unsanitized)

33
Q

how do you test for presence of halides

A

react with aqueous silver ions, forming silver halide precipitates

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

Inorganic Chemistry Year 12 (5 decks)

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