Halide Ions Flashcards
Trend in Reducing Power
Define
Reducing power of halides increases down the group.
To reduce something, the halide ion needs to lose an electron from its outer shell.
How easy this is depends on the attraction between the nucleus and outer electrons
Two reasons why attraction between nucleus and outer electrons of halides gets weaker as you go down the group
- The ions get bigger, so the electrons are further away from the positive nucleus.
- There are extra inner electron shells, so there’s a greater shielding effect
Further down the group a halide ion is…
The easier it loses electrons and the greater its reducing power
Reactions with Sulfuric Acid
All halides react with concentrated sulfuric acid to give a hydrogen halide as a product
Two Equations for Reaction of NaF or NaCl with H2SO4
Misty Fumes of…
NaF + H2SO4 –> NaHSO4 + HF.
NaCl + H2SO4 –> NaHSO4 + HCl.
HF or HCl
Two Equations for Reaction of NaBr with H2SO4
SO2 Fumes
Br2 Fumes
NaBr + H2SO4 –> NaHSO4 + HBr.
2HBr + H2SO4 –> Br2 + SO2 + 2H2O.
Choking fumes.
Orange fumes
Three Equations for Reaction of NaI with H2SO4
NaI + H2SO4 –> NaHSO4 + HI.
2HI + H2SO4 –> I2 + SO2 + 2H2O.
6HI + SO2 –> H2S + 3I2 + 2H2O
Describe H2S
Toxic and smells of bad eggs
Test for Halides (describe)
Add dilute nitric acid (to remove ions which might interfere with the test).
Then add a few drops of silver nitrate solution (AgNO3).
A precipitate is formed of a silver halide
Colour of precipitate of silver fluoride
No precipitate
Colour of precipitate of silver chloride
White precipitate
Colour of precipitate of silver bromide
Cream precipitate
Colour of precipitate of silver iodide
Yellow precipitate
How to be extra sure of results of test for halides?
Add ammonia solution
Describe result of silver chloride precipitate in ammonia
White precipitate.
Dissolves in dilute NH3
