FAIRFIELD METHODIST SCHOOL (SECONDARY)
SCIENCE DEPARTMENT
Secondary Four Express Pure Chemistry
Worksheet: Alcohols and Carboxylic Acids
Name: ________________________(
)
Class: ______
Date: ____________
Multiple-Choice Questions
1.
The structures of three compounds, X, Y and Z are shown below.
Which compounds are isomers?
A X and Y only
B X and Z only
C X, Y and Z
D Y and Z only
2.
[ C
]
What is the molecular formula of the ester formed when methanol reacts with butanoic acid?
A CH3COOC3H7
B C2H5COOC2H5
C C3H7COOC2H5
D C3H7COOCH3
[ D
]
[ D
]
3. Which statement is true about propanol?
A It is an unsaturated compound.
B It is formed by the oxidation of propanoic acid.
C It reacts with an acid to form ethyl ethanoate.
D It is formed by catalytic addition of steam to propene.
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4. The diagram shows the structure of propanoic acid.
How many moles of propanoic acid react with one mole of magnesium metal?
A 1
C 3
B
D
2
4
[ B
]
[ C
]
5. The properties of an organic compound, T, are shown below.
•
•
•
It reacts with aqueous sodium hydroxide.
It reacts with sodium carbonate solution.
It turns reddish-brown bromine water colourless.
What could be the structure of T?
A
B
C
D
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Structured Questions
1. The figure below shows the apparatus for the fermentation of sugar to produce ethanol.
a. Write the chemical equation for the reaction.
yeast
C6H12O6 (aq) →
2C2H5OH (aq) + 2CO2 (g)
b. Identify substance X.
yeast
c. State two conditions required for the reaction and explain why they are essential.
Absence of oxygen – to prevent ethanol from being oxidized to ethanoic acid by oxygen.
Temperature at 37°C – optimal temperature for enzymes in yeast to work. Higher
temperature causes the enzymes to denature and fermentation to stop.
d. Suggest a reason for the layer of oil in the test tube.
To prevent air from entering the mixture.
e. The Universal Indicator was observed to change from green to orange after a few days.
i.
What can be concluded about the gas produced?
The gas is acidic.
ii.
Suggest another function of the test tube containing Universal Indicator.
It acts as an air lock to prevent air from entering the mixture.
f.
It was found that the resulting mixture is a dilute solution of ethanol.
Suggest one method to obtain the pure ethanol from the mixture.
fractional distillation
g. Ethanol is also suitable to be used in perfumes and deodorants.
Suggest a physical property which explains why ethanol is suitable.
It is volatile and can evaporate easily.
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2. An alcohol with the molecular formula of C2H6O and a carboxylic acid with the molecular formula
of CH2O2 react to form an ester.
a. Write the chemical equation of the reaction, showing the structures of all organic
compounds.
+
→
b. The carboxylic acid is a weak acid.
i.
Explain why it is a weak acid.
It dissociates/ ionises partially to form H+ ions when dissolved in water.
ii.
Write the chemical equation for the reaction between calcium carbonate and the
carboxylic acid.
2HCOOH + CaCO3 → (HCOO)2Ca + CO2 + H2O
iii.
Draw the structure of the product formed when the carboxylic acid reacts with sodium
hydroxide.
− Na+
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3. The structural formulae of six organic compounds are shown below.
a.
Q
R
S
T
U
Name the organic compounds Q, R and S.
Q: propanol
b.
P
R: methyl ethanoate
S: propanoic acid
Identify two pairs of isomers.
P & Q, R &S
c.
Suggest a chemical test to distinguish between R and U.
Add aqueous bromine to R and U.
If aqueous bromine turns reddish-brown to colourless, the substance is U.
If aqueous bromine remains reddish-brown, the substance is R.
d.
T can be obtained from a reaction in the laboratory.
i.
Briefly describe the steps of the reaction, including the condition, catalyst and reagent
clearly.
Oxidation of butanol. Add acidified potassium manganate (VII) solution to butanol and
heat. Potassium manganate(VII) solution oxidized butanol to butanoic acid.
ii.
Write an equation for the reaction in (d)(i), showing the structural formula of all the
organic compounds.
+ 2 [O] →
+ H2O
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4. Consider the following scheme which shows the reactions of some simple organic molecules.
a. Complete the table below for compounds A, B and F.
Compound
Name
A
ethane
B
ethene
F
ethyl ethanoate
Structural Formula
b. Identify the types of reactions for the following conversions.
i.
compound A to compound C substitution reaction (with chlorine)
ii.
compound B to compound C addition reaction (of hydrogen chloride)
iii.
compound D to compound E oxidation reaction
iv.
compounds D and E to compound F esterification
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c. Give the conditions necessary for the reactions described in
i. b(iii)
acidified potassium manganate(VII) solution, heat
ii. b(iv)
concentrated sulfuric acid, heat
d. Compound E reacts with sodium hydroxide to form water and sodium ethanoate.
Draw the full structural formula of E and circle the hydrogen that is replaced by sodium in
this reaction.
5. X is a colourless organic gas. It reacts with steam to form an alcohol and is able to form a
polymer. X has a relative molecular mass of 42.
a. Name compound X and draw its structural formula.
propene
b. From 200 tonnes of X, a manufacturer obtained 150 tonnes of alcohol. Calculate the
percentage yield of alcohol in this process. (1 tonne = 1000 kg)
no. of moles of X
200 000 000
=
42
= 4761900 mol (5 s.f.)
theoretical mass of propanol formed
Percentage yield
= 4761900 × 60
= 285 710 000 g
= 285.71 tonnes
150
= 285.71 × 100%
= 52.5% (3 s.f.)
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