halogens Flashcards
state the appearances of F, Cl, Br and I at room temp
F = pale yellow gas
Cl = pale green gas
Br = brown liquid
I = grey solid
describe the trend in boiling point down the group
- increases
- atomic radius and relative mass increase
- so london forces are stronger
describe the trend in electronegativity down the group
- decreases
- atomic radius and shielding increase
- so nuclear attraction decreases and electrons are less easily gained
what is the use of hexane in displacement reactions?
makes observing colour change easier
describe what happens when a halogen is added to an organic solvent
- dissolves
- forms a layer
- ABOVE the aq organic layer
describe the trend in reactivity down the group
- decreases
- atomic radius increases
- nuclear attraction decreases
- electrons less easily attracted
what does the reactivity trend mean in terms of displacement?
- more reactive halogens displace less reactive halides
- halogens are less easily oxidised down the group so they displace halides LOWER DOWN
describe the reaction between chloride ions and chlorine
no reaction
colourless
describe the reaction between bromide ions and chlorine
Cl displaces Br
aq layer is yellow
organic layer stays orange
describe the reaction between iodide ions and chlorine
Cl displaces I
aq layer is yellow
organic layer stays purple
describe the reaction between bromide ions and chlorine
no reaction
describe the reaction between bromide ions and iodine
Br displaces I
aq layer is orange
organic layer stays purple
how is a halide tested for and confirmed?
- test with silver nitrate
- confirm with ammonia
state the 3 steps in testing for halides
- add dilute HNO3
- add AgNO3
- add NH3
what is the purpose of adding HNO3?
reacts with any anions other than halides
- eg carbonates
what is the observation when adding AgNO3?
Cl = white ppt
Br = cream ppt
I = yellow ppt
what is the observation when adding NH3?
Cl = dissolves in dilute
Br = dissolves in conc
I = insoluble in conc
what reaction forms bleach?
disproportionation
how is the formation of bleach a disproportionation reaction?
Cl is simultaneously oxidised & reduced
what is bleach used for?
- treat water
- bleach paper
- cleaning agent
what is meant by water sterilisation?
adding Cl to kill bacteria
what is the reaction between water and Cl2?
Cl2 + H2O –> HCl + HClO
what is the reaction between hydrogen chlorate and water?
HClO + H2O –> ClO- + H3O-
formation of chlorate ions
state 3 advantages of chlorinating water
- destroys micro organisms that cause disease
- long lasting as reduces bacteria build up down supply
- reduces algae growth
state 3 disadvantages of chlorinating water
- 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
what are the ethical implications of chlorinating water?
- no choice as occurs across UK
- forced medication
what are the alternatives to chlorinating water?
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
