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Chemistry Y12 > I- Group 7 Halogens > Flashcards

I- Group 7 Halogens Flashcards

1
Q

How to distinguish between aq solutions of bromine and iodine?

A
  • both red-brown in water
  • add hexane (non-polar solvent)
  • iodine turns purple
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2
Q

Why do halogens dissolve in water?

A
  • charge in H2O
  • attracts charge in temp dipole in halogen

Halogens still dissolve better in non-polar solvents

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3
Q

Explain why chlorine is the best oxidising agent among Cl2, Br2, I2.

A
  • Cl2 best at gaining e-
  • harder to gain e- down the group
  • larger atoms
  • ↑ shielding ∵ extra e- shell
  • ↓ attraction
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4
Q

Result when sodium bromide added to chlorine.

A
  • yellow solution
  • Br2 forms
  • + hexane –> red-brown
  • Cl2 + 2Br- –> 2Cl- +Br2

you can tell Cl2 is the oxidising agent as its oxidation state changes from 0 to -1.

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5
Q

Result when sodium iodide added to chlorine/ bromine.

A
  • brown solution
  • I2 forms
  • + hexane –> purple
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6
Q

Reaction when sodium chloride added to bromine

A
  • x reaction- stays yellow
  • + hexane–> red-brown (shows Br still present)
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7
Q

Reaction when sodium chloride/ bromide added to iodine.

A
  • x reaction- stays brown
  • + hexane–> purple (violet) (I2 still present)
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8
Q

Describe the steps for the test for halide ions.

A
  1. silver nitrate solution
  2. acidify w/ a few drops of nitric acid (to remove CO3 2- ions)
  3. halide solution –> record results
  4. dilute ammonia (ammonium hydroxide) –> record
  5. concentrated ammonia in fume cupboard + record
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9
Q

Testing for halide ions:
Observations for F-

3 steps

A
  1. AgNO3- x ppt
  2. dilute NH3- x further change
  3. conc. NH3- x further change
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10
Q

Testing for halide ions:
Observations for Cl-

3 steps

A

1 AgNO3- white ppt
- Ag+ (aq) + Cl- (aq) –> AgCl (s)
2 dilute NH3- soluble
- AgCl(s) + 2NH3(aq) –> [Ag(NH3)2]+ (aq) + Cl- (aq)
- diammine silver (I) [complex]
3 conc. NH3- x further change

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11
Q

Testing for halide ions:
Observations for Br-

3 steps

A

1 AgNO3- cream ppt.
- Ag+ (aq) + Br- (aq) –> AgBr (s)
2 dilute NH3- insoluble
3 conc. NH3- soluble
- AgBr(s) + 2NH3(aq) –> [Ag(NH3)2]+ (aq) + Br-

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12
Q

Testing for halide ions:
Observations for I-

A

1 AgNo3- yellow ppt
- Ag+ (aq) + I- (aq) –> AgI (s)
2 dilute NH3- insoluble
3 conc. NH3- insoluble

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13
Q

Physical appearances of halides (F2 - I2) at room temp

A
  • F2- pale yellow gas
  • Cl2- pale green gas
  • Br2- red-brown/ orange liquid
  • I2- grey solid –> sublimes–> violet vapour
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14
Q

Trends in physical properties of halides

A

down the group:
- darker
- denser

they all have ‘swimming bath’ smell

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15
Q

Predict the appearance of astatine

A
  • black solid (darker)
  • x contained in a container ∵ radioactive + short half life
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16
Q

Safety precautions with concentrated sulphuric acid (VI)

A

corrosive
- gloves + goggles

releases heat when reacted w. water –> run thru cold water for long time if in contct

17
Q

Test for reducing ability of halide ions

A
  1. spatula of sodium halide–> boiling tube
  2. conc. sulphuric acid (VI)- powerful oxidising agent
18
Q

Are fluorides and chlorides reducing agents?

A

No ∵ x reducing ability
- NaF + H2SO4 –> NaHSO4 + HF
- NaF= base (proton acceptor); H2SO4= proton donor
- Acid-base reaction (x redox!!!)

19
Q

Are bromides good reducing agents?

A

Weak reducing agent- S: +6 –> +4
1. NaBr + H2SO4 –> NaHSO4 + HBr (acid- base)
2. HBr –> H+ + Br-
3. 2H+ +2Br- +H2SO4 –> Br2 + SO2 + 2H2O

20
Q

Are iodides good reducing agents?

A

Strong reducing agents- S: +6 –> -2
1. NaI + H2SO4 –> NaHSO4 + HI
2. HI –> H+ + I-
3. 2H+ + 2I- + H2SO4 –> I2 +SO2 + 2H2O
4. 8H+ + 8I- + 2SO2 –> 4I2 + 2S + 4H2O
5. 6H+ + 6I- + SO2 –> H2S + 3I2 + 2H2O

21
Q

Observations of Cl- added to concentrated sulphuric acid (VI)

A
  • white steamy fumes of HCl gas
22
Q

Observations of Br- added to concentrated sulphuric acid (VI)

A
  1. white steamy fumes of HBr
  2. red-brown vapour Br2 ; SO2 w/ pungent smell
23
Q

Observations of I- added to concentrated sulphuric acid (VI)

A
  1. white steamy fumes of HI
  2. purple vapour, grey solid I2 ; SO2- pungent smell
  3. H2S- bad egg smell ; S- yellow solid
24
Q

Trend of reducing power down group 7

A

↑ reducing power
- easier to lose e- down the group
- larger ions
- ↑ shielding (extra e- shell)

25
Q

What is a disproportionation reaction?

A
  • a species being both oxidised & reduced in the same reaction
  • both the oxidising & reducing agent
26
Q

Eg. of a disproportionation reaction-
Cl + H2O

A

Cl2 (g) + H2O (l) ⇌ HClO (aq) + HCl (aq)
0 –> +1 & -1
- reversible
- HCl + chloric (I) acid

27
Q

What are the 2 uses of chloric (I) acid formed in the reaction of chlorine and water?

A
  1. bleaches
  2. kill bacteria
28
Q

Why is chlorine added into drinking water if it is toxic?

A

benefits to health (eg. prevents cholera) outweighs its toxic effects

29
Q

What is the disadvantage of using chlorinated water in outdoor swimming pools?

A

has to be replaced frequently
- ∵ lost easily in sunlight
- 2 Cl2 (g) + 2 H2O (l) –> 4HCl (aq) + O2 (g)

30
Q

What is a safer alternative to direct chlorination of water?

A

Add sodium chlorate (I)
+ in powder form- safer than Cl2 gas
+ easier to handle
+ X make Cl2 but still makes chloric acid (I) to kill bacteria
– NaClO (s) + H2O (l) ⇌ Na+ (aq) + OH- (aq) + HClO (aq)

31
Q

Eg. of disproportionation reaction- Chlorine + sodium hydroxide

A
  • x reversible
  • Cl2 (g) + 2NaOH (aq) –> NaClO (aq) + H2O (l)
  • Cl2 (g) + 2OH- (aq) –> ClO- (aq) + Cl- (aq) + H2O (l)
    – 0 –> +1 & -1
32
Q

Explain why the pH of outdoor swimming pools must be constantly monitored.

A
  • ↓pH = Cl reacting w/ water under sunlight –>HCl + O2
  • ↓ chloric (I) acid to kill bacteria
33
Q

Test for nitrates

A
  1. add a few drops of NaOH + warm
  2. damp red litmus held at end of test tube turns blue
  3. ammonia produced- alkaline
34
Q
A

Chemistry Y12 (33 decks)

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