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CHEMISTRY 3.5
WORKSHEET NINE
Name:
ORGANIC CHEMISTRY
Carboxylic acids and their derivatives #2
1.
After making an ester by heating a carboxylic acid with an alcohol in the presence of
concentrated sulfuric acid, water is added to the mixture and the ester separates out as an oily
layer that floats to the top and produces a strong fruity odour. Comment on the physical
properties of esters that these observations suggest.
2.
Lipids are triglycerides and their structure consists of a molecule of glycerol bonded through
three ester linkages to three “fatty” acids.
3.
(a)
Write the condensed structural formula for glycerol.
(b)
What is the systematic name for glycerol?
(c)
Draw the molecular structure of the lipid produced from glycerol and three molecules of
stearic acid (C17H35COOH).
(d)
Explain why an esterification reaction can be also described as a condensation reaction.
Because esters are made by forcing the equilibrium reaction between a carboxylic acid and an
alcohol to the right, it should also be possible to split an ester back into its constituents by
forcing the same equilibrium to shift itself in the reverse direction, ie to the left.
(a)
Write the equilibrium reaction between methanoic acid and ethanol that produces the
ester, ethylmethanoate.
(b)
If the forward reaction is called condensation, explain why the reverse reaction is called
hydrolysis.
(c)
Concentrated sulfuric acid was needed to force the equilibrium to the right and produce
the ester. Name the chemical that is commonly used to hydrolyse esters by moving the
equilibrium to the left.
(d)
Explain with the aid of an equation, how the chemical you have named in (c) acts to shift
the equilibrium in the desired direction.
4.
Amides can be produced from the reaction of esters with ammonia but the reaction is slow.
What is the preferred method of production of amides?
5.
Name the following substances.
(a)
CH3CH2CONH2
(b)
HCONH2
6.
Amides are crystalline solids at room temperature and the lower members are soluble in water.
Explain these properties in terms of the bonding involved.
7.
Write an equation for the preferred method of production of ethanamide.
8.
Like esters and acyl chlorides, amides can also undergo hydrolysis and revert back to the
carboxylic acid that they were derived from.
(a)
Amides can be hydrolysed by heating with HCl. Write an equation for the reaction of
propanamide with HCl.
(b)
Amides can also be hydrolysed by heating with NaOH. Write an equation for the reaction
of propanamide with NaOH.