Halogens Flashcards
What are the uses of halogens?
Water purification
Bleaching agents
Flame-retardants
Fire extinguishers
Antiseptic/disinfectant
What is the colour of fluorine?
Pale yellow gas
What is the colour of chlorine?
Green/yellow gas
What is the colour of bromine?
Orange/brown liquid
What is the colour of iodine?
Grey/black solid, purple vapour
What is volatility?
How easily a substance can evaporate
How does volatility change down the group?
As boiling points increase, volatility decreases
What kind of molecules are halogens?
Diatomic, simple molecular with weak London forces
How does electronegativity change down the group?
Decreases
What is oxidising power?
Ability to accept an electron
How does the oxidising power change down the group?
Decreases
How does reactivity change down the group?
Decreases as they find it more difficult to attract incoming electrons needed to form 1- ion
What happens in displacement reactions?
A more reactive halogen displaces a less reactive one from a halide solution of the less reactive halogen
What kind of reactions are displacement reactions generally?
Redox - as the halide ion loses electrons and the halogen gains electrons
What happens when you add chloride solution to colourless potassium bromide solution?
Displacement reaction - solution becomes yellow - orange as bromine is formed
What happens when you add chloride solution to colourless potassium iodide solution?
Displacement reaction - solution becomes brown as iodine is formed
What happens if an organic solvent is added to potassium bromide solution?
Organic layer will appear yellow-orange as bromine is formed
What happens if an organic solvent is added to potassium iodide solution?
Organic layer will appear purple as iodine is formed
What do halogens act as?
Oxidising agents
What do chlorine and bromine oxidise?
Iron (ll) to Iron (lll)
Why doesn’t iodine oxidise Iron (ll)?
It is not a strong enough oxidising agent
What does Iron (lll) due to iodide ions?
Iodine is oxidised from iodide ions to iodine by Iron (lll)
What kind of reaction is the one between chlorine and a dilute alkali?
A disproportionation reaction - chlorine gets oxidised and reduced simultaneously
What is produced in the reaction between chlorine and a cold alkali?
Sodium chloride + sodium hypochlorite + water
Cl2 + 2NaOH = NaCl + NaClO + H2O
What is produced in the reaction between Chlorine and a hot alkali?
Sodium chloride + sodium chlorate + water
3Cl2 + 6NaOH = 5NaCl + NaClO3 + 3H2O
What can chlorine be used for in terms of water?
Can be used to clean it and make it drinkable
What is the reaction of chlorine with water?
Disproportionation
Produces hydrochloric acid and chloric acid
Cl2 + H2O = HCl + HClO
How does chloric acid sterilise water?
By killing bacteria
What can HClO further disassociate into in water?
H+ and ClO-
ClO- also acts as sterilising agent, cleaning the water
What is produced when chloride, bromide and iodide ions react with concentrated sulphuric acid?
A toxic gas is produced - needs to be carries out in a fume cupboard
What is the general reaction of halide ions with concentrated sulphuric acid?
H2SO4 + X- = HX + HSO4-
Produces a hydrogen halide
How is concentrated sulphuric acid added to sodium chloride crystals?
Dropwise
What is produced by the reaction of sodium chloride with concentrated sulphuric acid?
Hydrogen chloride gas and sodium sulphate
H2SO4 + NaCl = HCl + NaHSO4
What is the hydrogen chloride gas produced as? (from concentrated sulphuric acid)
White fumes
How does the thermal stability of hydrogen halides change down the group?
It decreases
What is the reaction of sodium bromide and concentrated sulphuric acid?
H2SO4 + NaBr = HBr + NaHSO4
What does concentrated sulphuric acid do to hydrogen bromide?
Oxidises it
What happens given that sulphuric acid oxidises hydrogen bromide?
It decomposes it into bromine and hydrogen gas
Sulphuric acid is reduced to sulphur dioxide gas
What is the reaction of hydrogen bromide and sulphuric acid?
2HBr + H2SO4 = Br2 + SO2 + 2H2O
What is bromine produced as? (after being oxidised with sulphuric acid)
A reddish-brown gas
What is the reaction of sodium iodide and sulphuric acid?
H2SO4 + Nal = Hl + NaHSO4
Does the sulphuric acid oxidise the hydrogen iodide?
Yes - to many extents
What is one way sulphuric acid oxidises hydrogen iodide?
To iodine (released as a purple/violet vapour) - l2
Sulphur dioxide - SO2
To water - H2O
What is another way sulphuric acid oxidises hydrogen iodide?
To iodine
To sulphur - seen as a yellow solid
To water
What is the final way sulphuric acid oxidises hydrogen iodide?
To iodine
To Hydrogen sulphide - has a strong smell of bad eggs
To water
How can halide ions be identified in an unknown solution?
Dissolving the solution in nitric acid
Adding a silver nitrate solution
Then adding ammonia solution
How do halide ions react with silver nitrate solution?
AgNO3 + X- = AgX + NO3-
Ag+ + X- = AgX
What will happen if an unknown solution contains a halide ion when added with silver nitrate?
A precipitate of the silver halide will be formed
How do we identify the halide ion after the silver halide precipitate has formed?
We add dilute and then concentrated ammonia
How do we tell if the halide is a chloride ion?
If the silver halide precipitate dissolves in dilute ammonia
How do we tell of the halide is a bromide ion?
If the silver halide precipitate does not dissolve in dilute ammonia but does in concentrated
How do we tell if the halide is a iodide ion?
If it dissolves in neither dilute nor concentrated ammonia
What is the colour of silver chloride solution?
White
What is the colour of silver bromide solution?
Cream
What is the colour of silver iodide solution?
Pale yellow
What happens when a halogen reacts with hydrogen?
A hydrogen halide is produced
What do hydrogen halides react with ammonia gas to form?
Ammonium halides
e.g. NH3 + HCl = NH4Cl
Do hydrogen halides react with water?
Yes
e.g. Hydrogen chloride dissolves in water to form hydrochloric acid
