C
1.4.2
Empirical and molecular formulae. Structural formulae and isomers.
Q.38
With the help of examples define what is meant by –
|
(a)
an empirical formula (b)
a structural formula |
(a)
a graphical formula (d)
a linear abbreviated formula |
Ans Empirical formula shows the simplest
whole number ratio for the atoms of different elements in a compound.
For example the empirical formula of glucose (molecular formula C6H12O6)
is CH2O.
The structural formula not only shows the numbers of different atoms
present but the way in which the atoms are arranged in the molecule.
The graphical formula is a diagrammatic
representation of the atoms in a compound and the way in which they are
arranged.
A
linear abbreviated formula is a hybridised form of the molecular and structural
formulas where they are combined to form a linear formula in which functional
groups are grouped together etc.
Q.39
Calculate
formula from experimental data.
Ans
Do Exercises 1.22-1.26 in ACC.
C1.4.3
Q.40
What is meant by the term ‘functional groups’?
Ans
The term functional group refers to the active part
of a molecule that determines the chemical reactions that that molecule
undergoes.
The
required functional groups are illustrated to the right.
Q.41
What is an ‘homologous series’?
Ans
A homologous series is a family of organic compounds containing the
same functional group and possessing the same general formula.
C1.4.4
Q.42
What effect does chain length have on physical properties.
Ans
As chain length increases the hydrocarbon chain has a greater effect
on the properties. The molecule
becomes more polarisible in nature and hence the melting and boiling points are
raised
Q.43
What are the trends in physical properties within a homologous series.
(NO treatment of Van der Waals’ forces expected here.)
Ans
C1.4.5
Q.44
Organic reactions can be classified as addition, substitution and
elimination. What are they?
Give a definition and examples for each.
Ans
Substitution
Where a molecule has one group /atom removed and replaced by another
E.g.
C C
Br +
OH-(aq)
"
C C
OH
Addition
Where two molecules react and combine to form a single molecule.
Double/triple bonds must be involved
Br
C
C
E.g.
C =
+
"
Br
Br
Br
Elimination
Where a single molecule has part of it removed to form two products, one
of which being unsaturated.
E.g.
C C
Br +
OH-(alc)
"
C = C
+ H2
C1.4.6
Q.45
Define what is meant by ‘the mechanism of a reaction’.
Ans
Frank
Q.46
With the help of examples explain what happens in
(a)
electrophilic mechanisms
Ans
This is an electron deficient species that will attack an eletron rich
centre.
(Electron lover) E.g.
Electrophillic addition
(b)
nucleophilic mechanisms.
Ans
This is an electron rich species that will attack an electron deficient
centre.
(Nucleus lover) e.G.
Nucleophillic substitution.
C1.4.7
Physical and chemical properties
of alkenes and cycloalkenes.
Q.47
Discuss the addition reactions of alkenes (& ethy???) and
cycloalkenes (e.g. cyclohexene) with
(a)
hydrogen: (hydrogenation)
Ans
H2 gas and ethene
Catalyst: finely divided platinum/palladium (Normal P + T)
Under P - 470K: Nickel
(b)
bromine: (bromination)
Ans
Liquid Br2/ solution of Br2 in CCl4 (Tetrachloromethene)
+
ethene
colourless oil : 1,2
dibroethane
(c)
bromine water
Ans
HbrO(aq) &
Br2(aq)
+
ethene
1,2 dibromoethane & 1, bromoethan, 2,ol.
(d)
hydrogen bromide
Ans
HBr(g/aq)
ordinary temps.
+
ethene
1, bromoethane
(e)
water
Ans
Hydration
Ethene + steam
ethanol
At 600K & 70atm
catalyst: Phosphoric (V)
acid
*Note addition of HBr to propene is not required.)
(f)
Outline the mechanism
Fiona
book under 48(a)
Q.48
Outline the formation of addition polymers include polythene,
polypropylene, PVC and polystyrene
Details of polymer structure, e.g. high and low density poly(ethene), are
NOT required. (cf. Section C4.4.1).
the mechanism of the reaction of hydrogen bromide and bromine with ethene.
Addition of hydrogen bromide to propene is NOT required
Ans
In addition polymerisation, small molecules join together to become a
single product – a polymer
H
H
H
H
H
H
C =
C
C =
C
C =
C
H
H
H
H
H
H
H H
H
H
H
H
C C
C
C
C
C
H H
H
H
H
H
H
H
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
H
C1.4.8
Physical and chemical properties of halogenoalkanes.
Details of SN1 and SN2 mechanisms are NOT required
in this section (cf. Section C2.4.7).
Q.49
Discuss the relative reactivity of tertiary, secondary and primary
halogenoalkanes.
Tertiary halogenoalkane (3°)
See
Fiona’s notes
(a)
–OH
Ans
Reflux with NaOH(aq) -
not alcoholic
H H
H
H
H
C
C
Br +
OH-
H
C
C
OH +
Br-
H H
H
H
(b)
Non-bonding
valence electron pair/lone pair
–NH2
2
Ans
H
N
H
H
The lone pair is a negative source, which, unbonded is able to attack a
positive centre – a nucleophile.
Answer
not completed yet.
(c)
– C= N
Ans
Q.50
Discuss the conditions and reagents needed for the elimination reactions
of halogenoalkanes to form alkenes.
Ans