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CHEMISTRY > 3.3 the halogens > Flashcards

3.3 the halogens Flashcards

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1
Q

fluorine

A

pale yellow gas

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2
Q

chlorine

A

pale green gas

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3
Q

bromine

A

brown-orange liquid

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4
Q

iodine

A

grey solid

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5
Q

boiling point trend down group 7

A

boiling point increases down group 7
London forces increase due to increasing size and relative mass

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6
Q

electronegativity trend down group 7

A

electronegativity decreases down group 7
atoms get larger
distance between nucleus and bonding electrons increases
also more shielding

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7
Q

what is electronegativity?

A

the ability for an atom to attract electrons towards itself in a covalent bond

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8
Q

what is the use of organic solvent?

A

to see colour changes easily
halogen present dissolves readily in organic solvent which forms a layer above aqueous layer
e.g. hexane

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9
Q

what happens in group 7 displacement reactions?

A

more reactive halogens displace less reactive halide ions

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10
Q

reactivity trends down group 7

A

reactivity decreases down group 7
smaller atoms attract electrons better than larger atoms
halogens are also less oxidising as we move down group 7

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11
Q

organic solvent colours

A

Br2 = orange
I2 = purple

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12
Q

test for halides

A

add dilute nitric acid (HNO3) then silver nitrate solution (AgNO3)
*confirm with ammonia solution

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13
Q

why do we add nitric acid first for halide testing?

A

nitric acid reacts with any other anions other than halides (e.g. carbonates) to avoid false results

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14
Q

results for further halide test using ammonia (NH3)

A

Cl- white ppt dissolves in dilute NH3
Br- cream ppt dissolves in conc NH3
I- yellow ppt is insoluble in conc NH3

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15
Q

what reaction is bleach made via?

A

disproportionation reaction
chlorine has been simultaneously reduced and oxidised

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16
Q

bleach formation

A

mixing chlorine and sodium hydroxide will form sodium chlorate(I) solution - also know as bleach

17
Q

bleach equation

A

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

18
Q

uses of sodium chlorate(I)
NaClO (bleach)

A
  • treating water
  • bleaching paper and fabrics
  • cleaning agents (bleach)
19
Q

water sterilisation

A

adding chlorine to water can kill bacteria in the water
produces chlorate ions (ClO-) which kill bacteria
useful in drinking water and pools

20
Q

equation for adding Cl2 to water

A

H2O(l) + Cl2(g) <–> HCl(aq) + HClO(aq)
DISPROPORTIONATION reaction

21
Q

Chloric(I) acid ionises to make chlorate(I) ions (hypochlorite ions)

A

HClO(aq) + H2O(l) <–> ClO-(aq) + H3O+ (aq)

22
Q

advantages of chlorinating drinking water

A
  • destroys microorganisms that cause disease
  • long lasting so reduces bacteria build up
  • reduces growth of algae that discolours water and can give it a bad smell/taste
23
Q

disadvantages of chlorinating drinking water

A
  • chloring gas is toxic and irritates the respiratory system
  • liquid chloring causes severe chemical burns to the skin
  • chloring can react with organic compounds present in water to make chloroalkanes which have been linked to causing cancer
24
Q

risk of not chlorinating water

A

lead to cholera epidemic

25
Q

ethical consideration of chlorinating drinking water

A

chlorination of water is mandatory across UK, some object to this claiming it is forced medication of a whole population

26
Q

alternatives to chlorination of water

A
  1. ozone - powerful oxidising agent that kills microorganisms but has a short half life so treatment is not permanent and is expensive to produce
  2. UV light - damages DNA in microorganisms however ineffective in cloudy water and does not prevent water becoming contaminated further down the process
27
Q

test for ammonium

A
  • add warm sodium hydroxide (NaOH), if ammonium compound is present, ammonia gas will be produced
  • used damp red litmus paper, turns blue when ammonia dissolves in water
28
Q

test for hydroxides

A

turn red litmus paper blue
hydroxides are alkaline
(NOT A PURE TEST)

29
Q

test for carbonates

A

add acid (HCl) which reacts with carbonate to produce CO2 gas
when CO2 gas is bubbled through limewater, it turns cloudy

30
Q

test for sulfates

A

add HCl to remove carbonates
add barium chloride (BaCl2)
white precipitate if sulfates are present
Ba 2+(aq) + SO4 2-(aq) -> BaSO4(s)

31
Q

order of ion tests

A
  1. carbonates (carbon dioxide gas produced)
  2. sulfates (barium sulfate precipitate)
  3. halides (white, cream, yellow precipitate)

CHEMISTRY (18 decks)

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