機 密 (只 限 閱 卷 員 使 用 )

CONFIDENTIAL (FOR MARKER’S USE ONLY)

香港考試及評核局
HONG KONG EXAMINATIONS AND ASSESSMENT AUTHORITY

2017年 香 港 中 學 文 憑
HONG KONG DIPLOMA OF SECONDARY EDUCATION 2017

CHEMISTRY PAPER 1 & COMBINED SCIENCE (CHEMISTRY)

SECTION B

MARKING SCHEME

本評卷參考乃香港考試及評核局專為今年本科考試而編寫，供閱卷員
參考之用。本評卷參考之使用，均受制於閱卷員有關之委任條款及閱
卷員指引。特別是：

- 本 局 擁 有 並 保 留 本 評 卷 參 考 的 所 有 財 產 權 利 ( 包 括 知 識 產 權 )。在 未
獲本局之書面批准下，閱卷員均不得複製、發表、透露、提供、
使用或經營本評卷參考之全部或其部份。在遵守上述條款之情況
下，本局有限地容許閱卷員可在應屆香港中學文憑考試的考試成
績公布後，將本評卷參考提供任教本科的教師參閱。

- 在任何情況下，均不得容許本評卷參考之全部或其部份落入學生
手 中 。 本 局 籲 請 各 閱 卷 員 /教 師 通 力 合 作 ， 堅 守 上 述 原 則 。

This marking scheme has been prepared by the Hong Kong Examinations and Assessment
Authority for the reference of markers. The use of this marking scheme is subject to the
relevant appointment terms and Instructions to Markers. In particular:

- The Authority retains all proprietary rights (including intellectual property rights) in
this marking scheme. This marking scheme, whether in whole or in part, must not
be copied, published, disclosed, made available, used or dealt in without the prior
written approval of the Authority. Subject to compliance with the foregoing, a
limited permission is granted to markers to share this marking scheme, after release
of examination results of the current HKDSE examination, with teachers who are
teaching the same subject.

- Under no circumstances should students be given access to this marking scheme or

any part of it. The Authority is counting on the co-operation of markers/teachers in
this regard.

香 港 考 試 及 評 核 局 保留版權
Hong Kong Examinations and Assessment Authority
All Rights Reserved 2017

2017-DSE-CHEM 1 & CS(CHEM) B–1

 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
INSTRUCTIONS TO MARKERS

1. In order to maintain a uniform standard in marking, markers should adhere to the marking scheme agreed
at the markers’ meeting.

2. The marking scheme may not exhaust all possible answers for each question. Markers should exercise
their professional discretion and judgment in accepting alternative answers that are not in the marking
scheme but are correct and well reasoned.

3. The following symbols are used:

/ A single slash indicates an acceptable alternative within an answer.

* Step-mark (for questions involving calculations)

† Correct spelling required

4. In questions asking for a specified number of reasons or examples etc. and a candidate gives more than
the required number, the extra answers should not be marked. For instance, in a question asking
candidates to provide two examples, and if a candidate gives three answers, only the first two should be
marked.

5. In cases where a candidate answers more questions than required, the answers to all questions should be
marked. However, the excess answer(s) receiving the lowest score(s) will be disregarded in the calculation
of the final mark.

6. Award zero marks for answers which are contradictory.

7. Chemical equations should be balanced except those in reaction schemes for organic synthesis. For
energetics, the chemical equations given should include the correct state symbols of the chemical species
involved.

8. In the question paper, questions which assess candidates’ communication skills are marked with an
asterisk (*). For these questions, the mark for effective communication (1 mark per question) will be
awarded if candidates can produce answers which are easily understandable. No marks for effective
communication will be awarded if the answers produced by candidates contain a lot of irrelevant
materials and/or wrong concepts in chemistry.

2017-DSE-CHEM 1 & CS(CHEM) B–2

 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Part I
Marks

1. (a) The metallic bond / electrostatic attraction (Not accept: giant metallic bond / metallic bone) 1
between delocalised electrons / sea of electrons and metal ions / barium ions / Ba2+. 1
(Not accept: free electrons / electrons / outermost electrons)
(Or diagram with correct labels)
(For diagram: (1) The barium ions should be labelled as “Ba2+” or “2+”
(2) Clearly indicates sea of electrons, or delocalised electrons between metal
ions.
(3) Clearly indicate metallic bond/electrostatic attraction between sea of
electrons / delocalised electrons and metal ions.)

(b) (i) The gas (ammonia) is less dense than air. 1

(Should be answered in terms of density. Not accept: The gas is lighter than air.)
(Not accept incorrect description of gas such as ammonium, NH 4, NH4+, HCl, etc.)

(ii) The gas (ammonia) is soluble (in water). 1

(Accept: The gas will be absorbed by water / The gas will react with water.)
(Not accept: The gas is slightly soluble in water.)

(c) (i) White solid forms / White precipitate forms / Heat evolves / Temperature rises / White 1
ppt forms
(Accept: Milky mixture forms / Cloudy mixture forms / White suspension forms.)

(ii) (1) When H2SO4(aq) is added to it, BaSO4(s) (and H2O(l)) are formed, the concentration 1
/ number of mobile ions in the mixture decreases / [Ba2+] and [OH] decrease.

(2) Excess H+(aq) and SO42(aq) ions are introduced into the solution . / 1
The concentrations / amounts / numbers of H+(aq) and SO42(aq) ions in the solution
increase. /
The concentration / amounts / numbers of (mobile) ions increases when H2SO4 is in
excess.
(Accept only H+ or SO42 is mentioned in the answer.)

2. (a)  Copper is not so easily oxidised/corroded as iron. 1

(Accept: Iron reacts with water/oxygen/air/acids but copper does not.)
(Not accept: Iron rusts but copper does not. / Copper does not so easily rust as iron.)
 Copper has a lower tendency to lose electrons than iron. / 1
Copper occupies a lower position than iron in the e.c.s. / metal reactivity series. /
Copper is less reactive than iron.

(b) (i) To lower the melting point of soldering materials. 1

(Not accept: The melting point of lead is low.)

(ii) Lead is / Compounds of lead are toxic / poisonous. (Not accept harmful) 1
(Accept: Lead will damage / is harmful to the central nervous system (or other internal
organs).)

(c) (1.0 × 108 ×1000) ÷ 207.2 1*

= 4.83 × 108 (mol dm3) 1
(Accept 4.8, 4.83, 4.826. Not accept 4.830)
(Accept answer without an unit, but NOT accept answer with an incorrect unit.)

2017-DSE-CHEM 1 & CS(CHEM) B–3

 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Marks

3. (a) A propene molecule has C=C bond whereas propane molecule has not. 1
(Accept: Carbon double bond.)
(Not accept: Propene is unsaturated while propane is saturated. / Propene is an alkene while
propane is an alkane.)

(b)  HO2C(CH2)4CO2H is a di-functional molecule / has two –CO2H groups / has two 1
function groups (to react with –NH2 group).
On the other hand, CH3(CH2)4CO2H is a mono-functional molecule / has only one
–CO2H group / has only one function group (to react with –NH2 group).
 Each HO2C(CH2)4CO2H molecule can react with two H2N(CH2)6NH2 molecules to form 1
a chain, while CH3(CH2)4CO2H can only react with one H2N(CH2)6NH2 molecule and
cannot form a chain.

(c)  The O atom in H2O has lone pairs of electrons. 1

 H+ does not have electrons in its outermost shell. 1
 Dative covalent bond formed between the O atom in H2O and H+ by sharing electron 1
pair.

(Also accept graphical answer as below:)

4. (a) (i) A: OH(aq) ions are (preferentially) discharged to give a (colourless) gas (oxygen). 1
(Accept oxygen is not mentioned. Not accept incorrect gas is mentioned.)
(Not accept: OH(aq) ions are preferentially discharged to give oxygen.)

(ii) B:
 H+(aq) ions are (preferentially) discharged to give a (colourless) gas (hydrogen). 1
(Accept hydrogen is not mentioned. Not accept incorrect gas is mentioned.)
(Not accept: H+(aq) ions are preferentially discharged to give hydrogen.)
 The solution turns pink as [OH(aq)] > [H+(aq)] (when H+ ions are consumed). 1
(Accept pink, red, purple, purplish red, reddish purple, magenta)
(Accept only mentioned concentration of OH / amount of OH / no. of mole of
OH increases / accumulate more OH , without mentioning H+.)

(b) 2H2O  2H2 + O2 1

(State symbols not required. Incorrect answer if wrong state symbols were given.)

(c) (i) A: No change. OH(aq) ions are (still preferentially) discharged to give a colourless gas 1
(oxygen).

(ii) B:
 No change. H+(aq) ions, the only cations, discharged to give a colourless gas 1
(hydrogen).
(Accept: A faster rate of colourless gas bubble formation will be observed with
increased concentration of H+ in the solution.)
 No colour change in the solution / The solution will not turn into pink as it is still 1
acidic, despite the decrease in [H+(aq)] / as H+(aq) is in excess.
(Accept: The solution close to the surface of the electrode will turn pink due to the
discharge of H+, but the overall colour change will become much less obvious / the
solution remains colourless due to the presence of excess H+ in the solution.)

2017-DSE-CHEM 1 & CS(CHEM) B–4

 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Marks

5.  Both molecules of H2 and F2 are held by weak van der Waals’ forces. 1
 The van der Waals’ forces between F2 are stronger that those between H2 because larger size 1
of F2 than H2.
(Accept: F2 molecule has more electrons than H2 molecule; Not Accept: F2 has a higher
molecular mass than H2)
 Hydrogen bond exists among HF molecules and hydrogen bond is stronger than van der 1
Waals’ forces.
For CS:
5. (a)  The curve starts rising from point (0,0), the slope decreases gradually and becomes a 1
horizontal line at the 3rd minute.
 The total volume of gas obtained is 60 cm3. 1

(If the curve was drawn as two segments of broken straight lines, only “the total volume of gas
obtained is 60 cm3”can be awarded 1 mark.)

(b) 60 cm3 of gas would be collected because the number of moles of H2O2 is the same for both 1
experiments. /
60 cm3 of gas would be collected because increasing the temperature will only increase the rate
of the reaction (but not affect the amount of product formed).

(Not accept ambiguous answer like “same amount of H2O2”)

2017-DSE-CHEM 1 & CS(CHEM) B–5

 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Marks

6. (a) oxidising and corrosive 1

(b) (i) The reaction between concentrated sulphuric acid and NaOH(aq) is highly exothermic. / 1
Concentrated NaOH is corrosive. / Avoid to fill the burette more than once. / Use less
chemicals.
Do not accept answer like “splashed out” without mentioning of “highly exothermic.”

(ii) red to orange 1

Do not accept “red to yellow”.

(iii) No. of moles of NaOH used = 0.189 × 22.20 × 10–3 = 4.20 × 10–3 1*
Concentration of the concentrated H2SO4
= 4.20 × 10–3 ÷ (2 × 25 × 10–3) × (1000 ÷ 5) 1*
= 16.8 (mol dm–3) 1
Correct Unit.
Accept 16.76, 16.78, 16.783, 16.784, 16.80 (mol dm–3).
Do not accept 16.7832 mol dm-3.

(c) Copper dissolves. / The solution turns blue. / A colourless/choking gas (bubbles) evolves. 1
Cu + 2H2SO4 → CuSO4 + 2H2O + SO2 (Accept ionic equation) 1
or (1)
The liquid turns black / A black solid/precipitate is formed）. (1)
Cu + H2SO4 → CuO + H2O + SO2 (Accept ionic equation)
State symbols not required.

7. (a) The reaction between carbon and hydrogen does not only give ethyne. / There will be side 1
reactions. / Side products will be formed
Carbon and hydrogen gas have no reaction at room conditions..

(b) The total enthalpy change of a chemical reaction is independent of the pathway between the 1
initial and final states.
ΔHf
(c) (i) 2C(graphite) (s) + H2(g) C2H2(g) 2

+2O2(g) 2ΔHc(graphite) +1/2 O2(g) ΔHc(H2(g)) +5/2 O2(g) ΔHc(C2H2(g))

2CO2(g) + H2O(l)
(Require correct state symbols.)

(ii) (1) 298K / 25oC and 1 atm / 101 kPa / 101325 Nm-2 1

(2) ΔHfo [C2H2(g)] = 2×(-394) + (-286) - (-1300) 1

= +226 kJ mol–1 1
Correct Unit.
Must show the positive sign.

2017-DSE-CHEM 1 & CS(CHEM) B–6

 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Marks

8. (a) 2C8H18 + 25O2 → 16CO2 + 18H2O 1

State symbols not required. The stoichiometric coefficients should be whole numbers.

(b) 1

Accept drawings showing electrons in the inner shells.

(c)  ‘For’: Using carbon capture techniques, the CO2 produced in power stations can be 1
trapped and stored, thus, the emission of carbon dioxide into the atmosphere will be
reduced. / Compared with petrol-driven car, power stations have higher energy
efficiency, and will reduce CO2 emissions. / Using renewable energy sources like solar
energy to power the electric car will reduce CO2 emissions.
 ‘Against’: The electricity used in powering car is mainly produced by burning of fossil 1
fuels, and the CO2 so produced will still be emitted into the atmosphere. / Producing
batteries for electric car will increase CO2 emissions.

(d) limited supply of air or oxygen / too large amount of petrol 1

(e) (i) catalytic converter † 1

Do not accept convertor.

(ii) particulates / suspended particulate / sulphur dioxide / PM 1

Do not accept nitrogen dioxide.

2017-DSE-CHEM 1 & CS(CHEM) B–7

 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Marks

9.  Acidified K2Cr2O7(aq) test: only HOCH2CH2CH2OH will produce a orange to green colour 1
change. / The other three liquids give negative result.
or
Acidified / neutral KMnO4(aq) test: only HOCH2CH2CH2OH or CH2=CHCO2H will produce
a purple to colourless/brown colour change. / The other two liquids give negative result.
 Br2(in organic solvent) test: only CH2=CHCO2H will produce a brown/orange to colourless 1
colour change. / The other three liquids give negative result.
or
Br2(aq) test: only CH2=CHCO2H will produce a brown/orange/yellow to colourless colour
change. / The other three liquids give negative result.
or
Acidified / neutral KMnO4(aq) test: only HOCH2CH2CH2OH or CH2=CHCO2H will produce
a purple to colourless/brown colour change. / The other two liquids give negative result.
 Add each liquid into water, 1
Mg / Zn test: only CH3CH2CO2H or CH2=CHCO2H reacts to give a colourless gas (bubbles) / 1
hydrogen gas / H2(g). / The other two liquids give negative result.
or
CO32- / HCO3- test: only CH3CH2CO2H or CH2=CHCO2H reacts to give colourless gas (1)
(bubbles) / carbon dioxide gas / CO2(g). / The other two liquids give negative result.
or
Esterification: With conc H2SO4 and heat/warm, only CH3CH2CO2H or CH2=CHCO2H reacts (1)
with an alkanol (e.g. ethanol) to give a pleasant smell. / The other two liquids give negative (1)
result.
or
Neutralisation: Only CH3CH2CO2H or CH2=CHCO2H reacts with an alkali (e.g. NaOH(aq)) /
a base and water to give out heat. / The other two liquids give negative result.

 CH3CO2CH3(l) gives a negative result in the above three chemical tests.

Do not accept tests like smell, pH/litmus paper, indicator, solubility in water, etc..
Accept other reasonable tests like the use of PCl3.

 Communication mark 1

(chemical knowledge = 0 to 2, mark = 0,

chemical knowledge = 3 to 4, mark = 0 or 1,
incomplete answer / difficult to understand / no distinguishing intention, mark = 0)

2017-DSE-CHEM 1 & CS(CHEM) B–8

 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Part II
Marks

10. (a) (60÷24000) × 2 = 0.005 y 1*

y = 1.0 mol dm3 1
(Accept answer without an unit, but NOT accept answer with an incorrect unit.)
(Accept maximum 3 decimal places)

(b)  The curve starts from point (0,0), the slope decreases and becomes a horizontal line at 1
the 3rd minute.
 The total volume of gas obtained is 60 cm3. 1

(If the curve was drawn as two segments of broken straight lines, only “the total volume of gas
obtained is 60 cm3”can be awarded 1 mark.)

(c) 60 cm3 of gas would be collected because the number of moles of H2O2 is the same for both 1
experiments. /
60 cm3 of gas would be collected because increasing the temperature will only increase the rate
of the reaction (but not affect the amount of product formed).
(Not accept ambiguous answer like “same amount of H2O2”)

(d) Follow the change in (total) pressure / mass in the system. 1

(Accept: Monitor the system with a pressure gauge / an electronic balance)

11. (a) Kc = [H+(aq)] [A(aq)] / [HA(aq)] 1

where HA represents 4-nitrophenol and A represents 4-nitrophenoxide ion.
(Accept no state symbols are given in the expression)

(b) In the solution, 2.4 = log [H+(aq)] 1*

[H+(aq)] = 4.0 × 103 mol dm3 (Accept 3.98 × 103 ~ 4.0 × 103 mol dm3) (1*)
(Accept no unit was given. Not accept incorrect unit)
8.0 x 108 = 4.0 × 103 [A(aq)] / [HA(aq)]
[HA(aq)] / [A(aq)] = 50000 (Accept 49750 ~ 50000, 4.975 × 104 ~ 5 × 104) 1
(Also accept [A(aq)] / [HA(aq)] = 1/ 50000 or 2 × 105 ~ 2.01 × 105)

(c)  The equilibrium position will shift to right when H+ ions are consumed by NaOH(aq). 1
(Also accept: The rate of the backward reaction decreases / HA will decompose to
compensate for the loss of H+, forming more A)
 HA is colourless while A is yellow. Increase in [A] causes the solution changes from 1
colourless to yellow / the colour/yellow colour becomes more intense.

(d) Indicator / use to find out the end-point of acid-base titration 1

2017-DSE-CHEM 1 & CS(CHEM) B–9

 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Marks

12. (a) CH3CH2CH(Br)CH2CH3 / CH3CH2CHBrCH2CH3 1

(b) (i)  The OH group in B will change to Br group in C by HBr, and there is no chiral 1
carbon due to no optical activity.
(Accept: B is an alcohol as B reacts with HBr to have a Br group in C.)
 Thus the structure of B is CH3CH2CH(OH)CH2CH3 / CH3CH2CHOHCH2CH3. 1

(ii) Substitution (†) 1

(c) (i) A has a C=C (or a C=O) double bond as there are 2 hydrogen atoms less in A as 1
compared with B.

A is optically active, so it has a chiral carbon.

＊ ＊ 1
A has the structure CH2=CHCH(OH)CH2CH3 / CH2=CHCHOHCH2CH3.

(ii) H2 / Pd (heat), or H2 / Pt (heat), or H2 / Ni (heat) 1

13. O O 3
1. NaOH(aq), heat
O OH
+
2. H (aq)
OH
O
1. LiAlH4, (dry ether)
(Not accept NaBH4) OH
OH

2. H+(aq) OH
OH
(intermediate: 1 mark; reagent for each step: 1 mark)

(For 1st step:

1. Reagent accept: OH, NaOH or NaOH(aq); Not accept NaOH(s) or solid NaOH.
2. Reagent accept: H+ / H2SO4 / H2SO4(aq), or HCl / HCl(aq)
3. For acid hydrolysis/base hydrolysis, “heat” is required.
4. Accept COONa+ as the intermediate (with corresponding matching reagent)
5. Not accept O―Na for the intermediate)

(For 2nd step:

1. If the intermediate is incorrect, but it still has the –COOH group, and the scheme shows a
correct reduction reaction, 1 mark for the reagent if the reagent is correct.
2. Accept –COONa+ as the intermediate for LiAlH4 reduction if the 1st step is alkaline
hydrolysis without acidification.
3. Not accept LiAlH4 in acidic medium.
4. Acidification is required after reduction with LiAlH4. LiAlH4 and acidification should be
expressed clearly as two steps.
5. Accept “dry ether” is omitted in the LiAlH4 step.)

2017-DSE-CHEM 1 & CS(CHEM) B–10

 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Marks

14.  2MnO4(aq) + 5C2O42(aq) + 16H+(aq) → 2Mn2+(aq) + 10CO2(g) + 8H2O(l) 1

(State symbols not required) (Ignore incorrect state symbols)
 Manganese exhibits variable oxidation numbers. The oxidation number of manganese changes 1
from +7 in MnO4 to +2 in Mn2+ in the reaction.
 Manganese forms coloured ions in aqueous solution. MnO4(aq) ions exhibit purple / 1
Mn2+(aq) ions exhibit pale pink.
 From the graph, it shows that the reaction rate increases when Mn2+ ions form / when the 1
reaction proceeds.
(Mention about Mn2+ is required. Not accept mentioning about other incorrect species such
as MnO4.)
 Manganese has catalytic properties. Mn2+ ions act as a catalyst for the reaction. 1
 Communication mark 1
(chemical knowledge = 0 to 2, communication mark = 0
chemical knowledge = 3 to 5, communication mark = 0 or 1
Incomplete answer / difficult to understand, communication mark = 0)

2017-DSE-CHEM 1 & CS(CHEM) B–11

 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)

香港考試及評核局
HONG KONG EXAMINATIONS AND ASSESSMENT AUTHORITY

2017年 香 港 中 學 文 憑
HONG KONG DIPLOMA OF SECONDARY EDUCATION 2017

CHEMISTRY PAPER 2

MARKING SCHEME

本評卷參考乃香港考試及評核局專為今年本科考試而編寫，供閱卷員參
考之用。本評卷參考之使用，均受制於閱卷員有關之委任條款及閱卷員
指引。特別是：

- 本 局 擁 有 並 保 留 本 評 卷 參 考 的 所 有 財 產 權 利 ( 包 括 知 識 產 權 )。在 未 獲
本局之書面批准下，閱卷員均不得複製、發表、透露、提供、使用
或經營本評卷參考之全部或其部份。在遵守上述條款之情況下，本
局有限地容許閱卷員可在應屆香港中學文憑考試的考試成績公布
後，將本評卷參考提供任教本科的教師參閱。

- 在任何情況下，均不得容許本評卷參考之全部或其部份落入學生手
中 。 本 局 籲 請 各 閱 卷 員 /教 師 通 力 合 作 ， 堅 守 上 述 原 則 。

This marking scheme has been prepared by the Hong Kong Examinations and Assessment
Authority for the reference of markers. The use of this marking scheme is subject to the
relevant appointment terms and Instructions to Markers. In particular:

- The Authority retains all proprietary rights (including intellectual property rights) in
this marking scheme. This marking scheme, whether in whole or in part, must not be
copied, published, disclosed, made available, used or dealt in without the prior written
approval of the Authority. Subject to compliance with the foregoing, a limited
permission is granted to markers to share this marking scheme, after release of
examination results of the current HKDSE examination, with teachers who are teaching
the same subject.

- Under no circumstances should students be given access to this marking scheme or any
part of it. The Authority is counting on the co-operation of markers/teachers in this
regard.

香 港 考 試 及 評 核 局 保留版權
Hong Kong Examinations and Assessment Authority
All Rights Reserved 2017

2017-DSE-CHEM 2–1
 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)

INSTRUCTIONS TO MARKERS

1. In order to maintain a uniform standard in marking, markers should adhere to the marking scheme agreed
at the markers’ meeting.

2. The marking scheme may not exhaust all possible answers for each question. Markers should exercise
their professional discretion and judgment in accepting alternative answers that are not in the marking
scheme but are correct and well reasoned.

3. The following symbols are used:

/ A single slash indicates an acceptable alternative within an answer.

* Step-mark (for questions involving calculations)

† Correct spelling required

4. In questions asking for a specified number of reasons or examples etc. and a candidate gives more than
the required number, the extra answers should not be marked. For instance, in a question asking
candidates to provide two examples, and if a candidate gives three answers, only the first two should be
marked.

5. In cases where a candidate answers more questions than required, the answers to all questions should be
marked. However, the excess answer(s) receiving the lowest score(s) will be disregarded in the calculation
of the final mark.

6. Award zero marks for answers which are contradictory.

7. Chemical equations should be balanced except those in reaction schemes for organic synthesis. For
energetics, the chemical equations given should include the correct state symbols of the chemical species
involved.

2017-DSE-CHEM 2–2
 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Marks

1. (a) (i) (1) N2 + 3H2 2NH3 1

[NOT accept  / =]
(2) The reaction mixture is cooled to condense ammonia to liquid. 1
[Accept: The reaction mixture is condensed / is cooled to liquid.]
(ii) The order of reaction with respect to A is zero, 0 / rate = k[A]0. 1
From the graph, rate of change of [A] is independent to [A] /a constant. 1
[Accept: A straight line is obtained. / [A] and time has a linear relationship / The slope of
the line is a constant.
NOT accept: [A] is directly proportional to time]

(iii) flammable / inflammable / toxic / poisonous 1

[NOT accept harmful]
(b) (i) 3
(potential energy)

2SO2(g)
O2(g)

2SO3(g)

(reaction coordinate / reaction coordination)

 1 mark for exothermic; i.e. energy of products is lower than that of reactants & Eact
of the catalysed reaction is lower
 1 mark for two steps for the one with catalyst (i.e. two peaks) & one/multiple steps
for the energy profile without catalyst
 1 mark for the labels of (2)SO2 & O2 and (2)SO3
 [NOT accept: reactants & products]
If the candidate did not use dotted line, marks can still be given if the diagram is clear. If
you cannot determine, mark will not be given.
If the candidate drew two separate sketches of energy profiles, do not give the first mark
(i.e. exothermic etc.). The subsequent marks can still be given.
If the candidate reversed the labels of axes, consider to give the 3rd mark.

(ii) (1) Impurities in the reaction mixture may poison the catalyst. 1
[Accept: Adsorb / The active sites of the catalyst are occupied by impurities.
NOT accept: the catalyst is poisoned by the reactants]
(2) (I) Lowering the temperature makes the reaction proceed at a slower rate. 1
[NOT accept lower fuel cost]
(II) The percentage conversion is already very high. / Increasing the pressure 1
can only lead to a very small increase in the percentage conversion but
very high cost is needed.
[Require to mention “percentage conversion” & “cost”.]
(3) Oxygen is used in a slight excess because it is more cost-effective/ cheaper to 1
obtain / easier to obtain.
[Requires a comparative sense.]

(c) (i) CH4 + H2O → CO + 3H2 1

[Accept NOT accept =]
(ii) (1) 2Cl– → Cl2 + 2e– 1

(2) Na+ + e– → Na 1
OR Na+ + Hg + e- → Na/Hg

2017-DSE-CHEM 2–3
 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Marks

(3) Mercury is poisonous. 1

[NOT accept harmful.]

(iii) Let rate = k[CO]m[Cl2]n

From doubling [CO] while keeping [Cl2] unchanged,
2.83 = 2 m 1
m = 1.5 [Accept 1.50, 1.501] 1

(iv) (1) The atom economy is 100% in the reaction. / No solvent is required in the 1
reaction.
[Accept: The atom economy is high]
(2) The reactants / (CO / Cl2) are poisonous / toxic. 1
NOT accept harmful.

2017-DSE-CHEM 2–4
 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Marks

2. (a) (i) Cross-linkages/covalent bonds/disulphur linkages are formed between polymer chains / 1
carbon atoms and sulphur atoms.
C C C C C C

S S S S

S S S S

C C C C C C

S S S S

S S S S

C C C C C C
With cross-linkages, the polymer chains cannot slip easily over each other / strong 1
attractive forces between the polymer chains.

(ii) The structure of HDPE is less branched than that of LDPE. (Do not accept crystallinity) 1

(iii) Yes, A exhibits liquid crystal behaviour. A molecule of A has a

- rigid central part / cyclic structure, 1
- polar group / ester group, 1
- long alkyl chain / rod like structure. (1)

(b) (i) (1) coordination number = 12 1

(2) number of Cu atoms = 12 × (1/4) + 1 = 4 (Need to show deduction) 1

（Accept 8 × (1/4) + 4 × (1/4) + 1 etc.）

(ii) (1) hexagonal close-packed (†) 1

(2) Similarity: coordination number (12) / close-packed structures / packing efficiency 1

(74%).

(3) Difference:
 Cu has A-B-C type packing or suitable descriptions 1
 Zn has A-B type packing or suitable descriptions 1

(iii) Brass (†) 1

(c) (i) CH2=C(CH3)CO2CH3 or 1

(Need to show the double bond)

petroleum / crude oil 1

(ii) contact lens 1

(iii) (1) Thermoplastic is a type of plastic that becomes softened /liquid when heated and 1
hard again when cooled.
Do not accept “molten” / “dissolve”

(2)  Production: Biomass is raw material / renewable resources. 1

 Disposal: PHB is biodegradable / degrade readily by bacteria/enzymes. 1

(iv) (1) Small molecules (e.g. H2O) will be eliminated in the reaction.. 1

(2) Disposal: PHB undergoes hydrolysis / decomposition in the presence of acids / 1

alkalis.

2017-DSE-CHEM 2–5
 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Marks

3. (a) (i) Flame test(s) are carried out. 1

Sodium ions give an intense golden yellow flame while potassium ions give a lilac flame. 1

(ii) Add a piece of filter paper which is soaked with acidified K2Cr2O7 to the gas, 1
the paper turns from orange to green. 1
OR Pass the gas to Cr2O72-/H+ (or MnO4-/H+).
The solution turns from orange to green (or purple to colourless / pale pink)
[No acidification: 0 mark]
OR It decolourises petals temporarily.
OR It turns Br2(aq) from brown/orange to colourless.
1 mark for correct reagent and 1 mark for correct observation

(iii) H H 1

O O

or

(b) (i) From (yellowish)green to pale pink 1

(ii) (1) (37.62+37.58+37.60) ÷ 3 = 37.60 cm3 1

[NOT accept 37.6]
Must show step and unit

(2) number of moles of Fe2+ ions formed in Step (1)

= 0.0282 × 37.60 × 103 × 5 × 10 1*
= 0.0530
number of moles of Fe3+ ions reacted in Step (1) = 0.0530 (1*)

[Accept 37.785 / 37.79 / 37.6 for 37.60

Range: 0.053 – 0.0533]

number of moles of HONH2 reacted = 0.875 ÷ 33.0 1*

= 0.0265 (1*)

mole ratio of HONH2 : Fe3+ = 1 : 2 1

3

(3) The oxidation number of iron changes from +3 to +2 and the oxidation number of
N in HONH2 is 1.
Since the mole ratio of HONH2 : Fe3+ = 1 : 2,
the oxidation number of N in this oxide = 1+2 [Can be presented in words] 1*
= +1 1
2
(iii) N2O 1

2017-DSE-CHEM 2–6
 機 密 (只 限 閱 卷 員 使 用 )
CONFIDENTIAL (FOR MARKER’S USE ONLY)
Marks

(c) (i) (1) The solvent / product will not lose due to heating. 1

(2) 2

water out

(extract)
water in
heat (solvent)

1 mark for correct experimental set-up, 1 mark for correct labels

Experimental set-up: 0 mark for closed system, wrong position of thermometer /
delivery tube etc.
[Accept: No cold water to condense.the solvent.]
1 mark for labelling heat, water in and water out

(3) (column) chromatography / thin layer chromatography / TLC / GCMS 1

[NOT accept C]
(ii) W 1
It has >C=O / carbonyl group as it has a strong absorption (peak) at around 1700 cm–1 in 1
its IR spectrum. [Y OR W; NOT X and Z]
It has no -COOH / carboxyl group as it does not react with NaHCO3(aq). [NOT Y] 1
[NOT accept NaHCO3(s)
Accept: From the given information in IR spectrum, it has >C=O group
From the given information on the reaction with NaHCO3, it has no –CO2H
group.
NOT accept: From the given information, it has >C=O / no –CO2H group (i.e. without
further elaboration)]

2017-DSE-CHEM 2–7