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SAMPLE CHEMISTRY QUESTIONS
MIXTURE OF UNIT 3 & 4 MATERIALS
QUESTION 1
The equation describing the production of butyl ethanoate is given below.
Catalyst
C 4 H 9 OH ( aq )  CH 3 COOH ( aq )  CH 3 COOC 4 H 9 ( aq )  H 2 O( l )
0.0500 mol of ethanoic acid and 0.0500 mol of butanol were allowed to reach equilibrium at
90 0 C for 2 hours, and then quickly cooled in an ice bath to 25 0 C . The reaction was carried
out at a constant volume of 1.00 dm 3 .
50.00 cm 3 of 1.00 M NaOH was added to the mixture, and was then titrated with 1.00 M
hydrochloric acid using phenolphthalein as the indicator. 33.30 cm 3 of acid was required for
this reaction.
CH 3 COOH ( aq )  NaOH ( aq )  CH 3COONa ( aq )  H 2O( l )
NaOH ( aq )  HCl ( aq )  NaCl ( aq )  H 2 O( l )
a.
(i)
Calculate the amount, in mol, of NaOH that reacted with the 1.00 M hydrochloric
acid solution.
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1 mark
(ii) Calculate the amount, in mol, of CH 3 COOH that reacted with the 1.00 M NaOH
solution.
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2 marks
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Unit 3 & 4 Chemistry - Mixed Questions
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(iii) Calculate the amount, in mol, of butanol, C 4 H 9 OH , that reacted in the initial
mixture.
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2 marks
(iv) Hence calculate the amount, in mol, of each species at equilibrium at 25 0 C .
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2 marks
b.
(i)
Write an expression for the equilibrium constant for this reaction.
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1 mark
(ii) Hence determine the equilibrium constant at 25 0 C .
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1 mark
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Unit 3 & 4 Chemistry - Mixed Questions
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c.
The table below describes some features relating to the organic molecules involved in
the production of butyl ethanoate.
Catalyst
C 4 H 9 OH ( aq )  CH 3 COOH ( aq )  CH 3 COOC 4 H 9 ( aq )  H 2 O( l )
Ethanoic Acid
Butanol
Butylethanoate
(i)
Molar Mass ( g / mol )
Boiling Point ( o C )
60.1
74.1
116
118.0
117.3
126
Explain how heating the equilibrium mixture to 110 o C will improve the yield of
ester.
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2 marks
(ii) What catalyst is typically used in the production of esters and why?
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1 mark
(ii) The reactants used to make small chain esters are highly soluble in aqueous
solutions, but the esters themselves are not. Explain.
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2 marks
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Unit 3 & 4 Chemistry - Mixed Questions
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d.
Esters may be linked to produce long chains known as polyesters. Could the
molecules below be used to produce a polyester? Explain your answer.
O
||
CH 3  C  O  CH 2  CH 3
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2 marks
Total 16 marks
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Unit 3 & 4 Chemistry - Mixed Questions
Page 4
QUESTION 2
A student decides to investigate the equilibrium properties and rates of the reaction involving
vitamin C ( C 6 H 8 O6 ) and iodine ( I 2 ) solution, as described in the reaction below.
C 6 H 8 O6 ( aq )  I 2 ( aq )  C 6 H 6 O6 ( aq )  2 HI ( aq )
Equimolar amounts of vitamin C and iodine were originally added to a vessel at 25 o C . The
concentration of iodine was then monitored using colorimetry at a wavelength of 400 nm.
The absorption of a series of standard solutions containing iodine, which is brown in colour,
is given below.
A sample of the reaction mixture was removed at 30 second intervals. The reaction was
stopped and the absorbance of each sample was determined using colorimetry. The
absorbances were then plotted against time, as illustrated in the graph below.
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Unit 3 & 4 Chemistry - Mixed Questions
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a.
(i)
At what time did the system described by the reaction
C 6 H 8 O6 ( aq )  I 2 ( aq )  C 6 H 6 O6 ( aq )  2 HI ( aq ) reach equilibrium?
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1 mark
(ii) What is the concentration of iodine when the system reaches equilibrium?
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1 mark
b.
(i)
Write an expression for the equilibrium constant for this reaction.
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1 mark
(ii) If the equilibrium constant for the formation of C6 H 6O6 ( aq ) is 3.125 M at the given
temperature, determine the concentration of C6 H 6O6 ( aq ) when the system reaches
equilibrium.
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3 marks
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Unit 3 & 4 Chemistry - Mixed Questions
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c.
(i)
On the axes below, sketch one possible curve that reflects the changes in
absorbance you could expect to observe if a catalyst was added to the reaction
mixture.
2 marks
(ii) On the axes below, sketch one possible curve that reflects the changes in
absorbance you could expect to observe if C 6 H 6 O6 ( aq ) were regularly removed
from the reaction mixture, keeping volume and temperature constant.
2 marks
Total 10 marks
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Unit 3 & 4 Chemistry - Mixed Questions
Page 7
QUESTION 3
The production of ethanol from ethene is given by the reaction:
H3PO4
C 2 H 4 ( g )  H 2 O( g )  C 2 H 5 OH ( g )
a.
Identify the type of reaction that is occurring in the above equation. Circle the
correct response(s):
Addition
Substitution
Hydration
Condensation
Esterification
1 mark
The graph below shows the variation in the equilibrium constant for this reaction at different
temperatures.
K
Temperature
b.
(i)
Use this graph to determine whether the production of ethanol is exothermic or
endothermic.
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1 mark
(ii) State whether the formation of ethanol is favoured by high or low pressures and
temperatures.
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2 marks
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Unit 3 & 4 Chemistry - Mixed Questions
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Most of our ethene supplies are derived from cracking of select fractions from crude oil.
c.
(i)
Write two equations to represent the cracking of propane.
Equation 1:
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Equation 2:
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1+1 = 2 marks
(ii) Explain why alkenes are produced during the cracking process.
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1 mark
Alkenes are typically more reactive than their corresponding alkanes due to the presence of
unsaturated C-C bonds.
d.
Outline a procedure to compare the reactivity of an alkene such as ethene with its
corresponding alkane. Describe the results that would be obtained, including the
relevant chemical equations.
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4 marks
Total 11 marks
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Unit 3 & 4 Chemistry - Mixed Questions
Page 9
QUESTION 4
The high cost of traditional hydrocarbon fuels has led to intense research into alternative
fuels such as ethanol.
Ethanol is a common alcohol with molar mass 46 gmol−1, density 0.789 g/ml and a heat of
combustion of 1409.4 kJmol−1.
a.
A group of students decide to investigate the energy released during the combustion of
ethanol using a form of calorimetry, as illustrated below.
Thermometer
Ethanol
The results obtained during this investigation include:
Volume of water in the beaker
500 ml
Volume of ethanol used during combustion
5.00 ml
Initial temperature of the water
22.4°C
Maximum temperature of the water
75.2°C
Note: Specific heat capacity of water
4.184 J−1g−1°C−1
(i)
What amount of energy was released when the ethanol was burned?
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1 mark
(ii) Why is the measured heat of combustion in this investigation lower than the true
heat of combustion for ethanol?
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1 mark
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Unit 3 & 4 Chemistry - Mixed Questions
Page 10
(iii) Use the results of this experiment to write the corresponding thermochemical
equation for the combustion of ethanol.
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4 marks
b.
Assume that all the heat released during the combustion of the ethanol sample in this
investigation was transferred to the water.
(i)
Determine the calibration factor of this “calorimeter” in kJ°K−1.
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2 marks
(ii) A 15.0 ml sample of pure olive oil contains 505 kJ of energy. What temperature
change should the students observe during the complete combustion of a 2.50 ml
sample using the illustrated “calorimeter”?
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2 marks
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Unit 3 & 4 Chemistry - Mixed Questions
Page 11
c.
Olive oil contains 55-85% oleic acid (CH3(CH2)7CHCH(CH2)7COOH) by weight.
(i)
What type of fatty acid is oleic acid?
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1 mark
(ii) State one difference that would be observed in the physical properties of olive oil if
it contained 85% stearic acid (CH3(CH2)16COOH) by weight?
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1 mark
Total 12 marks
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Unit 3 & 4 Chemistry - Mixed Questions
Page 12
QUESTION 5
Consider the flow diagram below, which shows the pathways of ingested fat and
starch in humans.
Triglyceride
Starch
A
Fatty Acid
+
CH 3 (CH 2 )14 COOH
Glycerol
Glucose
C3 H 8O3
C6 H12O6
 O2
CO2  H 2O
a.
(i)
State the type of reaction involved in process A.
(ii) Explain what is meant by the term “ triglyceride”.
(iii) Determine the correct molecular formula of the triglyceride .
1 + 1 + 3 = 5 marks
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Unit 3 & 4 Chemistry - Mixed Questions
Page 13
b.
(i)
When 0.200 g of pure glucose is completely combusted in a calorimeter,
3114J of energy is released. Calculate the H in kJmol -1 for the oxidation
reaction below.
C6H12O6 (s) + 6O2(g)  6CO2(g) + 6H2O (l)
(ii) The reaction above occurs in all living animal cells and is termed respiration.
Give one major difference between the manner in which glucose is oxidized
in living cells compared to its oxidation in a bomb calorimeter.
(iii) Excess glucose in the blood that does not undergo oxidation in cells is
converted to other substances. One possible pathway is the conversion of
glucose to fat. State the other possible pathway for glucose that occurs in animal
cells.
(iv) Glucose is very soluble in water. Describe, using a diagram if you wish,
the nature of the chemical bonding responsible for this observation.
2 + 1 + 1 + 2 = 6 marks
Total 11 marks
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Unit 3 & 4 Chemistry - Mixed Questions
Page 14
QUESTION 6
When phenol red, C19 H 14 O5 S is dissolved in water, the following equilibrium is set up.
C19 H 14 O5 S  C19 H 13O5 S   H 
Yellow
Red
In aqueous solutions, the molecule C19 H 14 O5 S is yellow, and the ion C19 H 13O5 S  is red.
Phenol red is a weak acid, whose K a  1.3  10 8 at 25 o C .
a.
(i)
Write the expression for the acid dissociation constant.
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1 mark
(ii) Calculate the concentration of hydrogen ions in a 0.0030M solution of phenol red.
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2 marks
b.
Another solution of phenol red, also at a concentration of 0.0030 M, is 1.5% hydrolysed
at 35 o C .
(i) Calculate the K a for the dissociation reaction of phenol red at 35 o C .
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2 marks
 The School For Excellence 2013
Unit 3 & 4 Chemistry - Mixed Questions
Page 15
(ii) Use these results to determine whether the forward reaction for the dissociation of
phenol red is endothermic or exothermic.
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1 mark
c.
Phenol red can be used as an acid/base indicator, changing from yellow to red
between pH 6.8 – 8.4.
Phenol red was used as the indicator in the following titration. A 0.105 M solution of
sodium hydroxide was slowly added from a burette, to a conical flask containing
20.00 ml HCl and a few drops of phenol red. A titre of 23.65 ml was required during this
titration.
(i)
What was the initial colour displayed by the indicator? Explain.
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2 marks
(ii) Explain why the indicator changes colour when excess sodium hydroxide is added
to the conical flask.
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2 marks
(iii) Calculate the molarity of the HCl solution.
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1 mark
Total 11 Marks
 The School For Excellence 2013
Unit 3 & 4 Chemistry - Mixed Questions
Page 16
QUESTION 7
The following structures represent some biologically important molecules.
A
B C18 H 34 O2
C C3 H 8 O3
D
E
F CH 3 (CH 2 )14 COOH
G CH 3COOH
H C12 H 22 O11
I C16 H 32 O2
J CO(NH 2 ) 2
K CO2
L
H 2 NCHCH 3COOH
H 2 COH
H 2O
O
HC        O    C    (CH 2 )16 CH 3
M
H 2 COH
a.
Circle the response(s) that best answer the questions below.
(i)
Which structure(s) represent fatty acids?
A
B
C
D
E
F
G
H
I
J
K
L
M
(ii) Which structure(s) represent the components from which unsaturated fats are
derived?
A
B
C
D
E
F
G
H
I
J
K
L
M
(iii) Which structure(s) represent the product(s) of photosynthesis?
A
B
C
D
E
F
G
H
I
J
K
L
M
(iv) Which structure(s) represent the product(s) of the hydrolysis of carbohydrates?
A
B
C
D
E
F
G
H
I
J
K
L
M
(v) Which structure(s) represent the product(s) of the oxidation of fats?
A
B
C
D
E
F
G
H
I
J
K
L
M
5 marks
 The School For Excellence 2013
Unit 3 & 4 Chemistry - Mixed Questions
Page 17
 The School For Excellence 2013
Unit 3 & 4 Chemistry - Mixed Questions
Page 18
b.
The nutritional information relating to 5 grams of a particular food that is based on the
components of larger molecules in Part (a) is given below.
Structure A
Structure B
Structure E
0.007 grams
4.1 grams
0.03 grams
The energy available to the body from the combustion of foods is given below.
Nutrient
Energy Available (kJ/g)
Carbohydrates
Fats
Proteins
17
37
17
Calculate the energy content per 100 gram serving of this food.
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2 marks
Total Marks = 7
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Unit 3 & 4 Chemistry - Mixed Questions
Page 19