2021-DSE
CHEM
PAPER 2
你 問 我 答
HONG KONG DIPLOMA OF SECONDARY EDUCATION EXAMINATION 2021
MOCK 1
CHEMISTRY PAPER 2
(1 hour)
This paper must be answered in English
INSTRUCTIONS
(1)
This paper consists of THREE sections, Section A, Section B and Section C. Attempt ALL
questions in any TWO sections.
(2)
Write your answers in the DSE(D) Answer Book provided. Start each question (not part of a
question) on a new page.
(3)
A Periodic Table is printed on page 8 of this Question Paper. Atomic numbers and relative
atomic masses of elements can be obtained from the Periodic Table.
Not to be taken away before the
end of the examination session
©你問我答
保留版權
All Rights Reserved 2021
2021-DSE-CHEM-M1 2−1 ©你問我答
1
Section A
Industrial Chemistry
Answer ALL parts of the question.
1.
(a)
Answer the following short questions :
(i)
Suggest ONE disadvantage of a simple electrolytic setup using carbon electrodes in
chloroalkali industry.
(1 mark)
(ii)
Sketch a Maxwell-Boltzmann distribution curve of molecular kinetic energy to illustrate
the effect of a catalyst on a chemical reaction involving a gaseous species.
(2 marks)
(iii)
Vitamin C is an essential nutrient for humans. Its deficiency can cause scurvy. To meet
the market demand, some effective industrial processes are used in the production of
vitamin C.
(1)
State a progress of the industrial production of vitamin C.
(2)
Hence, explain why it is regarded as a progress.
(2 marks)
(b)
Methanol is an important feedstock for the production of acetic acid in the chemical industry. It
has to be manufactured industrially and massively to ensure a constant supply.
(i)
Methane is often converted to methanol in the industry partly because methanol can be
further turned into many useful organic compounds. Suggest another industrial benefit of
the conversion of methane into methanol.
(1 mark)
(ii)
Methanol can be used to produce acetic acid through its reaction with a component
of syngas. The reaction requires iridium (Ir) as the catalyst.
(iii)
(1)
Write a chemical equation for the reaction involved.
(2)
This way of manufacture is adopted widely in the industry since it saves capital
for being energy efficient. In terms of the steps involved, explain why this way is
deemed energy efficient.
(2 marks)
The reaction scheme below can also yield acetic acid :
(1)
Calculate the atom economy for the first step of this reaction scheme with respect
to bromomethane.
(2)
Is this reaction scheme greener than the reaction in (ii) ? Support your answer
with TWO reasons.
(4 marks)
2021-DSE-CHEM-M1 2−2 ©你問我答
2
1.
(c)
To investigate the kinetics of the reaction between 2-chloro-2-methylbutane and sodium
hydroxide in an alcoholic medium at room temperature, two experiments with different initial
concentrations of 2-chloro-2-methylbutane were performed. The graph below shows the variation
of the molarity of sodium hydroxide with time :
(i)
It is known that the alcoholic medium refers to the use of ethanol as the solvent. Suggest
ONE advantage of using ethanol over water.
(1 mark)
(ii)
Deduce the orders of reaction each with respect to 2-chloro-2-methylbutane and sodium
hydroxide.
(2 marks)
(iii)
Hence, state the rate equation for this reaction.
(1 mark)
(iv)
Sketch a graph showing how the rate of reaction varies with the molarity of 2-chloro-2methylbutane (y-axis : rate of reaction; x-axis : molarity of 2-chloro-2-methylbutane).
(1 mark)
(v)
The same setup for reaction 2 is repeated again, but at 100°C. The rate of reaction of
sodium hydroxide is found to be −4.98 × 10−3 mol dm−3 s−1. Calculate the activation
energy for this reaction.
(Gas constant R = 8.31 J K−1 mol−1)
(3 marks)
END OF SECTION A
2021-DSE-CHEM-M1 2−3 ©你問我答
3
Go on to the next page
Section B
Materials Chemistry
Answer ALL parts of the question.
2.
(a)
Answer the following short questions :
(i)
Suggest a reagent to obtain colloidal silver nanoparticles from silver nitrate solution. State
the colour change.
(2 marks)
(ii)
How should the alignment of liquid crystals be in order to avoid colour distortion in
curved displays ?
(1 mark)
(iii)
Melt blowing is a fabrication method where a polymer is melted and converted to
filaments with very small diameter. Which TWO of the following polymers are suitable
for melt blowing ?
nylon, urea-methanal, Kevlar, polypropene
(2 marks)
(b)
Poly(tetrafluoroethene) (PTFE) is a polymer widely used in daily life.
(i)
One common use of PTFE is in coating non-stick cooking ware.
(1)
Draw the repeating unit of PTFE.
(2)
With reference to its structure, explain why PTFE has a non-stick property.
(3 marks)
(ii)
Gore-Tex™ is a fabric membrane found in high-end waterproof and breathable clothing.
It is made from expanded PTFE, which is produced by rapid stretching of blocks of heated
PTFE. What structural features and properties make Gore-Tex™ both waterproof and
breathable ?
(2 marks)
(iii)
In terms of the production and the disposal of PTFE, explain why it is NOT considered
as a green material.
(2 marks)
(iv)
Suggest another use of PTFE.
(1 mark)
2021-DSE-CHEM-M1 2−4 ©你問我答
4
2.
(c)
Nickel is a common metal that finds wide use in alloy.
(i)
(ii)
Nitinol is an alloy of nickel and titanium and it is a shape-memory alloy. After cooling to
a low temperature, Nitinol has a crystal structure with the following unit cell :
(1)
State the meaning of the term ‘shape-memory alloy’.
(2)
Deduce the respective number of Ni atoms and Ti atoms in the above unit cell.
(3)
Upon heating, Nitinol has a cubic open structure. Sketch a unit cell of the open
structure of Nitinol.
(5 marks)
Cupronickel, an alloy of nickel and copper, is a common coinage metal. In 1993, some
Hong Kong one-dollar coins were made by nickel-plated steel in a bid to phase out coins
made by cupronickel, but this was not well received and the production of nickel-plated
steel $1 coins was discontinued. Nowadays those $1 coins are rare and they are popular
among collectors as they are magnetic.
(1)
Suggest ONE reason why the alloy, cupronickel, is used to make coins.
(2)
Suggest ONE reason why the nickel-plated steel $1 coins were not well received.
(2 marks)
END OF SECTION B
2021-DSE-CHEM-M1 2−5 ©你問我答
5
Go on to the next page
Section C
Analytical Chemistry
Answer ALL parts of the question.
3.
(a)
Answer the following short questions :
(i)
Briefly describe how the purity of a substance can be examined through melting point
measurement.
(1 mark)
(ii)
Suggest a chemical test to distinguish between CaCl2(aq) and Ca(OCl)2(aq).
(2 marks)
(iii)
Briefly describe how to purify C6H5COOH(s) using recrystallisation.
(2 marks)
(b)
The concentration of chloride ions in a river water sample was determined to investigate whether
a habitat is suitable for a certain aquatic species.
(i)
Mohr’s method can be used. It involves the following steps :
Step (1) :
Step (2) :
Step (3) :
250.0 cm3 of a river water sample was filtered. The filtrate was collected.
The pH of the river water sample was measured to be 5.8. Then, 10.0 cm3
of 1 M sodium carbonate solution was added to adjust the pH of the sample.
A standard 1.12 M silver nitrate solution was used to titrate the treated
sample using potassium chromate as an indicator. 15.0 cm3 of the solution
required 24.90 cm3 of the silver nitrate solution to reach the end point.
(1)
State the observation at the end point of the titration.
(2)
Why does the pH of the river water sample have to be adjusted in Step (2) ?
(3)
Calculate the concentration of chloride ions in the original river water sample.
(4 marks)
(ii)
The concentration of chloride ions can also be determined using colorimetry.
Hg(SCN)2(aq) and Fe3+(aq) are added to the solution. They react with chloride ions to
form dark red Fe(SCN)2+(aq). A calibration curve is then constructed as follows :
2021-DSE-CHEM-M1 2−6 ©你問我答
6
3.
(b)
(c)
(ii)
(1)
Given that the mole ratio of SCN− to Cl− is 1 : 1, what would be the chloride
concentration of a sample if it gives an absorbance of 0.410 ?
(2)
Explain why the colorimetric method is more suitable for measuring chloride
concentration in freshwater than Mohr’s method.
(4 marks)
To obtain hexanoic acid from hexan-1-ol, acidified potassium dichromate solution was allowed
to react with hexan-1-ol under reflux. The chromatograms from thin-layer chromatography (TLC)
of the reaction mixture were obtained every hour and are shown below. The stationary phase was
alumina and the mobile phase was dichloromethane.
(i)
Explain whether the reaction has completed at time = 3 hours.
(1 mark)
(ii)
After 3 hours, the reflux setup was disassembled. The reaction mixture was subjected to
liquid-liquid extraction using hexane and sodium chloride solution, and the organic layer
was collected. Draw a labelled setup for the liquid-liquid extraction.
(2 marks)
(iii)
The solvent in the organic layer was evaporated away, and the remaining contents were
purified with column chromatography. The stationary phase and the mobile phase were
silica gel and dichloromethane respectively.
(1)
Briefly describe the principle of column chromatography.
(2)
Three fractions corresponding to spots A, B and C were collected. Which spot on
the chromatogram would give a peak at m/z = 100 upon an analysis by mass
spectrometry ? Explain your answer.
(4 marks)
END OF SECTION C
END OF PAPER
2021-DSE-CHEM-M1 2−7 ©你問我答
7
2021-DSE-CHEM-M1 2−8 ©你問我答
8