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Preparation of metal chlorides (not explicitly Edexcel C2000 but useful)
Structural isomerism – molecules to be familiar with.
Iron (II) chloride: Pass dry HCl gas over heated iron filings.
Fe(s) + 2HCl(g) ➜
FeCl2(s)+ H2 (g)
Iron (III) chloride: Pass dry Cl2 gas over heated iron filings.
2FeCl3(s)
2Fe(s) + 3Cl2(g) ➜
Aluminium chloride: Pass dry Cl2 gas over heated aluminium foil.
2AlCl3 (s)
2Al(s) + 3Cl2(g) ➜
Draw the structural isomers of C 4H10O that are alcohols.
CH3CH2CH2CH 2OH
CH3CH2CH(OH)CH 3
(CH3)3COH
CH3CH(CH3 )CH2OH
butan-1-ol
butan-2-ol
2-methyl propan-2-ol
2-methyl propan-1-ol
These chlorides must be prepared under anhydrous conditions because water will hydrolyse
them to hydroxides. The apparatus used is the sublimation chamber. The CaCl2 guard tube on
the exit can be replaced with KOH to absorb unreacted gases if a fume cupboard is not
available.
Dry CaCl2
Also the ethers, CH 3CH2OCH2CH3, CH3CH2CH2OCH3 and CH3CH(CH3)OCH3?
Gas out
To what extent do the above molecules differ from one another physically?
Dry CaCl2
Gas in
Fe filings or
Al foil
metal chloride
sublimate
Keep cold
to condense
product
Heat
Amongst the alcohols, branching lowers the boiling points because the intermolecular
hydrogen bonding becomes hindered and because branching decreases surface area,
weakening the induced dipole forces. The alcohols have higher boiling points than the ethers,
because the alcohols possess hydrogen bonding and the ethers do not.
Isomerism – definitions and basic ideas.
Geometrical isomers
Isomers are different molecules made from the same set of atoms, or molecular formulae.
CH3
Structural isomers have the same molecular formula but a different structural formula, i.e. the
atoms are connect up in a different order.
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Butane CH3CH2CH2CH3 and methyl propane CH3CH(CH3)CH3 are chain isomers, they
have different carbon chains. This is also known as branch isomerism.
1-bromo butane CH3 CH2CH2CH2Br and 2-bromo butane CH3CH2CHBrCH3 are
positional isomers. They differ in the position of an atom or group (here the Br atom)
along an otherwise identical carbon chain.
Ethanol CH3CH2OH and methoxymethane CH3OCH3 are functional group isomers, they
differ by having different functional groups.
Stereo isomers have the same molecular formula and the same structural formula, differing only
in the spatial arrangement of their bonds.
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Cis but-2-ene and the trans isomers differ by having methyl groups arranged either on
the same side (cis), or opposite sides (trans), this is an example of geometrical
isomerism.
2-hydroxypropanoic acid exists as two non-superimposable mirror images, this is an
example of optical isomerism.
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H
C
CH3
C
H
CH3
C
H
CH3
C
H
Why can the above molecules exhibit geometrical isomerism?
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There is no free rotation about the C=C bond, due to sideways overlap of p orbitals.
Neither carbon atom has two identical groups attached.
Groups can be arranged either on the same (cis) or opposite (trans) side of the double bond.
The restriction of rotation does not always have to be caused by a C=C bond. Geometrical
isomerism can occur in cyclic structures, for example 1,2-dichlorocyclopropanes, 2,4dinitrophenyl hydrazines and some transition metal complexes, such as PtCl2(NH3)2.
NH 3
H3N
H 3N
Pt
Cl
Cl
cis
Cl
Pt
Cl
NH 3
trans
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