3.2.3.1 Trends in properties Flashcards
How can you identify halide ions?
All metal halides, except fluorides, react with silver ions in aqueous solution.
Solution is first acidified by adding dilute nitric acid. The nitric acid reacts with and removes impurities which would of produced a confusing precipitate
Add a few drops of silver nitrate solution
The colour of the precipitate indicates the halide ion
Why does bromine dissolve into hexane rather than water?
Strength of the bonding between solvent molecules is similar to the strength of bonding between simple covalent molecules and the solvent
Strength of bonds between water and bromine isn’t sufficient to overcome the hydrogen bonding
What are the properties of hydrogen halides?
All have the formula HX
All dissolve in water
All form acidic solutions due to formation of H+ ions
Are all gases
What are the colours and natural states of the halogens?
Fluorine = pale yellow gas Chlorine = green gas Bromine = red - brown liquid Iodine = black solid
What is the trend for bond energies of the halogens in their natural state?
Decreases down the group
However F - F is weaker than chlorine and bromine
What is the trend in electronegativities of the halogens?
Decreases in electronegativity down the group
This is because the shared pair of electrons becomes further from the nucleus the further down the group you get
What is the trend in melting and boiling points of the halogens?
Increase going down the group
This is due to increased size which increases the van der Waals forces
Additionally they become more volatile up the group
What is the trend in oxidising ability of halogens?
Oxidising ability increases going up the group
Fluorine = one of the most powerful oxidising agent one
What happens in a halogen displacement reaction?
A more reactive halogen displacing a halide in a compound
This is a redox reaction
A halogen will displace the ion of a halogen below it in the periodic table
What happens to halide ions in reactions?
They act as reducing agents
They lose electrons to become halogen molecules
What is the trend in reducing ability of halide ions?
Increasing reducing power down the group
This is because the ions are larger so are further from the nucleus and loses the electron more easily
How does sodium chloride react with concentrated sulfuric acid?
NaCl + H2SO4 = NaHSO4 + HCl
Chloride is a weak reducing agent
Similar reaction happens with sodium fluoride to produce hydrogen fluoride
How does sodium bromide react with concentrated sulfuric acid?
Two reactions occur: NaBr + H2SO4 = NaHSO4 + HBr 2H+ ➕ 2Br- ➕ H2SO4 = SO2 ➕ 2H2O ➕ Br2 Bromide are strong reducing agents to reduce sulfuric acid Redox reaction Exothermic
How does sodium iodide react with concentrated sulfuric acid?
NaI + H2SO4 = NaHSO4 + HI
Iodide is a stronger reducing agent so it reduces sulfuric acid even further
8H+ ➕ 8I- ➕ H2SO4 = H2S ➕ 4H2O ➕ 4I2
What happens when you add a metal halide (except fluorides) to silver ions in solution?
A precipitate of an insoluble silver halide is formed
Dilute nitric acid is first added to the halide solution to remove any carbonate or hydroxide ions which would confuse the result
