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Volume 26, Number 1, September 2016
Answers
Revision quizzes
Anne Hodgson
Isoprene: structural motif of organic chemistry (p. 6)
1
The two molecules of carvone are enantiomers (optical isomers) of each other, i.e. one
molecule is the mirror image of the other.
2
O
H
OH
Citral (found in lemongrass)
Menthol
O
α-pinene
Camphor
(used to make mothballs)
Squalene (note: there is one tail-to-tail connection in the squalene molecule)
O
O
Nepetalactone,
the active ingredient of catnip
Abietic acid
(found in pine resin)
HO
O
OH
Retinol (vitamin A)
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Lab page (p. 10)
1
The molecular formula of aspirin is C9H8O4
2
The empirical formula of ethanoic anhydride is C4H6O3 (which also happens to be its
molecular formula).
3
The ester functional group is
4
To calculate how many moles there are in 3.00 g of salicylic acid we first need to work out the
molecular mass of salicylic acid.
From the molecular formula (C7H6O3) of salicylic acid, the molecular mass (to the nearest whole
number) must be:
(7 ×12) + (6 × 1) + (3 × 16) = 84 + 6 + 48 = 138
so the mass of 1 mole of salicylic acid is 138 g
There are 3.00/138 = 0.022 moles of salicylic acid in 3.00 g.
5
Looking at the equation for the reaction (Figure 1) we can see that 1 mole of aspirin is
produced from 1 mole of salicylic acid.
From its molecular formula (C9H8O4), the relative molecular mass of aspirin (to the nearest whole
number) is:
(9 × 12) + (8 × 1) + (4 × 16) = 108 + 8 + 64 = 180
so the mass of 1 mole of aspirin is 180 g
There are 2.25/180 = 0.0125 moles of aspirin in 2.25 g of product.
We started with 0.022 moles of salicylic acid, so the percentage yield of aspirin in this reaction is:
0.0125/0.022 × 100 = 56.82%
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Volatile organic compounds: where do smells go?
(p. 22)
1
2
Lavender
and
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Cinnamon
Lemon
Petrol is a mixture of hydrocarbons containing 4 to 12 carbon atoms (for example octane). It also
contains some aromatic molecules (such as benzene), which contribute to its characteristic smell.
3
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Focus on industry (p. 33)
SO3H
N
N
H
O
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