I1: 10 Group 7, the Halogens Flashcards
What is the trend in electronegativity as you go down the halogens?
Electronegativity decreases.
This is because the atomic radius and shielding increase. The pair of electrons in the covalent bond is further away from the nuclear charge, making it harder to attract them.
What is the trend in boiling points as you go down the halogens?
Boiling points increase.
This is because larger atoms have stronger van der Waals forces between molecules.
What is the trend in oxidising ability as you go down the halogens?
Oxidising ability decreases.
This is because the atomic radius and shielding increase. The outer electrons are further away from the nuclear charge, making it harder to attract electrons.
What are the ionic equations of the displacement reactions of halide ions in aqueous solution?
Cl2 (aq) + 2Br- (aq) -> 2Cl- (aq) + Br2 (aq)
Cl2 (aq) + 2I- (aq) -> 2Cl- (aq) + I2 (aq)
Br2 (aq) + 2I- (aq) -> 2Br- (aq) + I2 (aq)
What is the trend in reducing ability as you go down the halogens?
Reducing ability increases.
This is because the atomic radius and shielding increase. The outer electrons are further away from the nuclear charge, making it easier to lose electrons.
What is the reaction of sodium chloride with concentrated sulfuric acid?
NaCl (s) + H2SO4 (l) -> NaHSO4 (s) + HCl (g)
HCl is formed - you’ll see misty fumes.
HCl isn’t a strong enough reducing agent to reduce the sulfuric acid so the reaction stops there.
Not a redox reaction.
What is the reaction of sodium bromide with concentrated sulfuric acid?
Also give the overall equation.
NaBr (s) + H2SO4 (l) -> NaHSO4 (s) + HBr (g)
2HBr (g) + H2SO4 (l) -> Br2 (g) + SO2 (g) + 2H2O (l)
The first reaction produces HBr - you’ll see misty fumes.
HBr is a stronger reducing agent and reacts with H2SO4 in a redox reaction.
Choking fumes of SO2 and orange fumes of Br2 will be produced.
Overall equation: 2NaBr + 2H2SO4 -> Br2 + Na2SO4 + SO2 + 2H2O
What is the reaction of sodium iodide with concentrated sulfuric acid?
NaI (s) + H2SO4 (l) -> NaHSO4 (s) + HI (g)
2HI (g) + H2SO4 (l) -> I2 (g) + SO2 (g) + 2H2O (l)
6HI (g) + SO2 (g) -> H2S (g) + 3I2 (s) + 2H2O (l)
The first reaction produces HI - you’ll see misty fumes.
The second reaction shows HI reducing H2SO4 to produce iodine (purple fumes) and sulfur dioxide (colourless, choking gas).
The third reaction shows HI continuing to reduce the SO2 to H2S (colourless gas with bad egg smell).
What is the test to identify halide ions?
- Add dilute nitric acid to remove ions which might interfere with the test.
- Add a few drops of silver nitrate solution (AgNO3).
Cl- = white precipitate of AgCl
Br- = cream precipitate of AgBr
I- = yellow precipitate of AgI
What is the test to distinguish between precipitated halide ions?
Add dilute ammonia solution (NH3).
AgCl dissolves in dilute ammonia solution.
Add concentrated ammonia solution.
AgBr dissolves in concentrated ammonia solution.
AgI doesn’t dissolve.
What is the trend in solubility of the silver halides in ammonia?
Solubility decreases
AgCl > AgBr > AgI
What is the reaction of chlorine with water?
Cl2 (g) + H2O (l) <-> HCl (aq) + HClO (aq)
Cl2 (g) + H2O (l) <-> 2H+ (aq) + Cl- (aq) + ClO- (aq)
What is the reaction of chlorine with water in the presence of sunlight?
2Cl2 (g) + 2H2O (l) <-> 4HCl (aq) + O2 (g)
2Cl2 (g) + 2H2O (l) <-> 4H+ (aq) + 4Cl- (aq) + O2 (g)
Why is chlorine used in water treatment?
Society assesses the advantages and disadvantages when deciding in chemicals should be added to water supplies.
Chlorate (I) ions kill bacteria but it’s used in small amounts and the health benefits outweigh the risks.
What is the reaction of chlorine with cold, dilute, aqueous NaOH?
Cl2 (g) + 2NaOH (aq) -> NaClO (aq) + NaCl (aq) + H2O (l)
Sodium chlorate (I) solution is used in bleach.
