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Chemistry > PMT Group 7 > Flashcards

PMT Group 7 Flashcards

1
Q

List 2 properties of halogens

A

● Low melting and boiling points

● Exist as diatomic molecules

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2
Q

What is the trend in boiling

point down group 7? Why?

A

Increases down the group because:

  • size of atom increases as more occupied electron shells
  • therefore stronger London forces of attraction between molecules
  • therefore take more energy to break
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3
Q

What is the trend in reactivity down group 7? Why?

A

Reactivity decreases because:
● Atomic radius increases
● Electron shielding increases
● Ability to gain an electron and form 1- ions
decreases due to lower attraction between that electron and the nucleus

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4
Q

Explain the trend of electronegativity down group 7

A

Down the group the electronegativity of the elements decreases.

This is because the atomic radii increases due to the increasing number of shells so
there is reduced nuclear attraction between the outermost electron and the nucleus.

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5
Q

What is the trend in oxidising

ability down group 7? Why?

A

Decreases down group (Cl strongest, I weakest)
This is because Cl has the fewest occupied electron shells,
greatest force of attraction between outer electrons and
nucleus and thus is the easiest to gain electrons and be
reduced → best oxidising agent

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6
Q

What is the trend in reducing
ability of the halides down the
group? Why?

A

Increases down the group (Cl- weakest, I- strongest)

I- has the most occupied electron shell so outer electrons are further from the nucleus, and so it has the weakest force of attraction between outer electrons and positive charge of nucleus.

Therefore it is the easiest to be oxidised and lose electrons → best reducing agent

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7
Q

Which species is oxidised in
this reaction:
Br2 (l) + 2Na (s) 2NaBr (s)

A

Na has been oxidised

Oxidation state of 0 to +1

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8
Q

When a more reactive halogen displaces a less reactive halide, what is the reaction called?

A

Displacement reaction

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9
Q

What is the colour of chlorine

in water?

A

Pale green

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10
Q

What is the colour of bromine

in water?

A

Orange

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11
Q

What is the colour of iodine in

water?

A

Brown

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12
Q

What is the colour of chlorine

in cyclohexane?

A

Pale green

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13
Q

What is the colour of bromine in cyclohexane?

A

Orange

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14
Q

What is the colour of iodine in

cyclohexane?

A

Violet

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15
Q

Out of the 3 halides Cl- , Br- & I- , which ones can be oxidised by chlorine?

A

Br- & I- ions

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16
Q

Write the equation for chlorine
oxidising bromide ions in water
and associated colour change

A

Cl₂ (aq) + 2Br- (aq) → 2Cl- (aq) + Br₂ (aq)

Yellow solution

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17
Q

Write the equation for Cl2
oxidising 2I- in cyclohexane
and associated colour change

A

Cl₂ (aq) + 2I- (aq) → 2Cl- (aq) + I₂ (aq)

Purple solution

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18
Q

Out of the 3 halides Cl- , Br- & I- , which one of these can be oxidised by bromine?

A

I- ions

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19
Q

Write the equation for bromine
oxidising iodide ions in water
and associated colour change

A

Br₂ (aq) + 2I- (aq) → 2Br- (aq) + I₂ (aq)

Brown solution

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20
Q

Out of the 3 halides Cl- , Br- &
I- , which one of these can be
oxidised by iodine?

A

Does not oxidise Cl-

or Br-

21
Q

Define disproportionation

A

The oxidation and reduction of the same

element in a redox reaction

22
Q

What is the equation for the
reaction of Cl2
with water?

A

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

23
Q

What type of reaction is the
reaction of chlorine with
water?

A

Disproportionation; chlorine is both

oxidised and reduced

24
Q

Why is chlorine added to

drinking water?

A

It kills the bacteria in the water and

makes it safer to drink

25
Q

What are the two forms of the

chlorate ion?

A

ClO- is chlorate (I)

ClO₃- is chlorate (V)

26
Q

What is the equation for
forming bleach and
conditions?

A

Cold dilute alkali
Cl₂ (aq) + 2NaOH (aq) → NaCl (aq) +
NaClO (aq) + H₂O (l)
NaClO is bleach

27
Q

Show that the reaction of
chlorine with hot dilute NaOH
is a disproportionation reaction

A 
3Cl2
 (aq) + 6 NaOH(aq) 5 NaCl (aq) + NaClO3
 (aq) + 3H2O (l) 
Chlorine is been reduced and oxidised.
Oxidation state of chlorine has gone from:
 0 to -1 in NaCl = reduction 
0 to +1 in NaClO3
 = oxidation
28
Q

What do you use to test for

halide ions?

A

Acidified AgNO3

29
Q

Why do you add HNO3
?
Why not HCl?

A

To remove CO₃2-
Adding HCl would add Cl- ions, giving a false
positive result

30
Q

Result and equation for Cl- test

A

White precipitate

Ag+ + Cl- –> AgCl(s)

31
Q

What is the result and

equation for the test for Br-?

A

Cream ppt

Ag+ + Br- → AgBr (s)

32
Q

What is the result and

equation for the test for I-?

A

Yellow ppt

Ag+ + I- → AgI (s)

33
Q 
What happens (+ equations) 
to each of the silver halide 
precipitates when 
dilute/conc NH3
 are added?
A

AgCl- dissolves in both dilute and conc
AgCl (s) + 2NH₃ (aq) → [Ag(NH₃)₂]+ (aq) + ClAg

Br- only dissolves in conc
AgBr (s) + 2NH₃ (aq) → [Ag(NH₃)₂]+ (aq) + Br

AgI- will not dissolve in either

34
Q

What is the trend in
oxidising ability down the
group? Why?

A

Decreases down group (Cl best, I worst)
Because: Cl has fewest occupied electron shells, greatest
force of attraction between outer electrons and nucleus,
easiest to gain electrons and be reduced → best oxidising
agent

35
Q

What is the trend in
reducing ability of the
halides down the group?
Why?

A

Increases down the group (Cl-
worst, I- best)
Because: I-
has the most occupied electron shells, so outer
electrons are further from the nucleus, weakest force of
attraction between outer electrons and positive charge of
nucleus → easiest to be oxidised and lose electrons → best
reducing agent

36
Q 
What products are formed 
when I-
 reduces H2SO4
? Do 
equations for all 4.
A

H₂SO₄ + 2I- → SO₄2- + 2HI

H₂SO₄ + 2H+ + 2I- → SO₂ + I₂ + 2H₂O (SO2 is a choking gas with a pungent odour)

H₂SO₄ + 6H+ + 6I- → S + 3I₂ + 4H₂O (S is a yellow solid)

H₂SO₄ + 8H+ + 8I- → H₂S + 4I₂ + 4H₂O (H2S smells of bad/rotten eggs)

37
Q

What are the products of Br-
+ H2SO4
?

A

HBr and SO₂

38
Q

Does Cl-
reduce H2SO4
?

A

No, not a powerful enough reducing agent; only

HCl is formed

39
Q

How can you test for
carbonate ions, CO3
2-?

A

Add strong acid to the sample
Collect the gas produced
Pass through lime water

40
Q

What are the observations for
a positive test of carbonate
ions, CO3
2-?

A

Fizzing

Limewater turns cloudy

41
Q

Write an equation for the

carbonate ion test

A

CO3
2- (aq) + 2H+
(aq) → H2O (aq) + CO2
(g)

42
Q

How can you test for sulfate
ions, SO4
2-?

A

● Add dilute hydrochloric acid and

barium sulphate to the sample

43
Q

What are the observations for
a positive test of sulfate ions,
SO4
2-?

A

White precipitate of barium sulfate is

produced

44
Q

Write an equation for the

sulfate ion test

A

Ba2+ (aq) + SO4
2- (aq) → BaSO4
(s)

45
Q

What do you use to test for

halide ions?

A

Acidified AgNO3

46
Q

When testing for carbonate,
sulfate and halide ions, in
which order should the tests
be carried out and why?

A
  1. Carbonate test
  2. Sulfate test
  3. Halide test
    Because barium ions forms insoluble precipitate of BaCO3
    and silver ions form insolube precipitate of Ag2SO4
47
Q

How can you test for
ammonium ions, NH4
+
?

A

Add sodium hydroxide to the sample and
warm it
Test the gas produced with red litmus paper

48
Q

What are the observations for

positive ammonium ions test?

A

● Red litmus paper turns blue

● Ammonia has a pungent smell

49
Q

Write the equation for

ammonium ions test

A

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

Chemistry (16 decks)

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