halogens

Question 1

state the appearances of F, Cl, Br and I at room temp

Answer 1

F = pale yellow gas
Cl = pale green gas
Br = brown liquid
I = grey solid

Question 2

describe the trend in boiling point down the group

Answer 2

• increases
• atomic radius and relative mass increase
• so london forces are stronger

Question 3

describe the trend in electronegativity down the group

Answer 3

• decreases
• atomic radius and shielding increase
• so nuclear attraction decreases and electrons are less easily gained

Question 4

what is the use of hexane in displacement reactions?

Answer 4

makes observing colour change easier

Question 5

describe what happens when a halogen is added to an organic solvent

Answer 5

• dissolves
• forms a layer
• ABOVE the aq organic layer

Question 6

describe the trend in reactivity down the group

Answer 6

• decreases
• atomic radius increases
• nuclear attraction decreases
• electrons less easily attracted

Question 7

what does the reactivity trend mean in terms of displacement?

Answer 7

• more reactive halogens displace less reactive halides
• halogens are less easily oxidised down the group so they displace halides LOWER DOWN

Question 8

describe the reaction between chloride ions and chlorine

Answer 8

no reaction
colourless

Question 9

describe the reaction between bromide ions and chlorine

Answer 9

Cl displaces Br
aq layer is yellow
organic layer stays orange

Question 10

describe the reaction between iodide ions and chlorine

Answer 10

Cl displaces I
aq layer is yellow
organic layer stays purple

Question 11

describe the reaction between bromide ions and chlorine

Answer 11

no reaction

Question 12

describe the reaction between bromide ions and iodine

Answer 12

Br displaces I
aq layer is orange
organic layer stays purple

Question 13

how is a halide tested for and confirmed?

Answer 13

• test with silver nitrate
• confirm with ammonia

Question 14

state the 3 steps in testing for halides

Answer 14

• add dilute HNO3
• add AgNO3
• add NH3

Question 15

what is the purpose of adding HNO3?

Answer 15

reacts with any anions other than halides
- eg carbonates

Question 16

what is the observation when adding AgNO3?

Answer 16

Cl = white ppt
Br = cream ppt
I = yellow ppt

Question 17

what is the observation when adding NH3?

Answer 17

Cl = dissolves in dilute
Br = dissolves in conc
I = insoluble in conc

Question 18

what reaction forms bleach?

Answer 18

disproportionation

Question 19

how is the formation of bleach a disproportionation reaction?

Answer 19

Cl is simultaneously oxidised & reduced

Question 20

what is bleach used for?

Answer 20

• treat water
• bleach paper
• cleaning agent

Question 21

what is meant by water sterilisation?

Answer 21

adding Cl to kill bacteria

Question 22

what is the reaction between water and Cl2?

Answer 22

Cl2 + H2O –> HCl + HClO

Question 23

what is the reaction between hydrogen chlorate and water?

Answer 23

HClO + H2O –> ClO- + H3O-

formation of chlorate ions

Question 24

state 3 advantages of chlorinating water

Answer 24

• destroys micro organisms that cause disease
• long lasting as reduces bacteria build up down supply
• reduces algae growth

Question 25

state 3 disadvantages of chlorinating water

Answer 25

• Cl gas is toxic and irritates respiratory system
• liquid Cl causes chemical burns
• Cl reacts with organic compounds to make chloroalkanes which can cause cancer

Question 26

what are the ethical implications of chlorinating water?

Answer 26

• no choice as occurs across UK
• forced medication

Question 27

what are the alternatives to chlorinating water?

Answer 27

ozone = oxidising agent which kills microrganisms
- short half life so not permanent
- expensive

UV = damages microorganisms DNA
- ineffective in cloudy water
- won’t prevent further contamination