HKDSE Chemistry
SBA Teachers’ Conference (2024/2025)
Date:
26 October 2024
Venue: Cheung Sha Wan Catholic Secondary School
Program
9:00 – 9:15
Registration
9:15 – 9:25
Introduction
Ms S C Chu
9:25 – 9:45
SBA Arrangement
Ms S C Chu
9:45 – 10:35
Supervisors’ Remarks
Dr K W Mak & Dr W H Fong
10:35 – 11:00
Sharing on SBA resources
Dr S L Cheng
11:00 – 11:15
Break
11:15 – 12:00
Group Meeting
******************************************************************
Materials available on HKEAA web page (http://www.hkeaa.edu.hk)
1.
2.
3.
4.
Handbook for School Leaders on SBA
SBA Teachers' Handbook
SBA Sample Tasks
Frequently Asked Questions
Materials related to Mark Submissions (https://www.hkdse.hkeaa.edu.hk)
1.
User Manual
********************************************************
Resource Materials
A.
Platform of Teacher Resources for Senior Secondary Chemistry, Science Education Section, EDB
(https://cd1.edb.hkedcity.net/cd/science/chemistry/teacher_resources/index.html)
B.
Learning and Teaching Resources on Practical Chemistry
Resource materials
Websites
1.
2.
Inquiry-based Chemistry Experiments
Learning and Teaching Activities for
the Revised Sixth Form Chemistry
Curriculum
Investigative Study in Chemistry –
Exemplars of Learning and Teaching
Activities
教育局教育多媒體–高中化學探究
研習
https://cd1.edb.hkedcity.net/cd/science/che
mistry/online_resources.html (English)
Chemistry Experimental Techniques
https://youtube.com/playlist?list=PLzsY_C
ILZpCFPSrM02tHLNkeLlXQ_YQp&si=pfr8PzWr
wGvdr6yh (English)
3.
4.
5.
https://cd1.edb.hkedcity.net/cd/science/che
mistry/online_resources_c.html (中文)
https://youtube.com/playlist?list=PLzsY_C
ILZpCHD081gallTU0fz66jb4Rfy&si=odu
hTvCCnd2rgoCD (中文)
6.
Practical Activities for Effective
Learning, Teaching and Assessment
of Chemistry
http://cuhk.edu.hk/proj/science_resource/C
HEM04/internal
7.
Teaching Kit on Chemical Testing for
Senior Secondary Curriculum
https://www.hkctc.gov.hk/en/career/edu/re
source_teaching_kit.html (English)
(English)
(中文)
(English)
(中文)
(English)
(中文)
https://www.hkctc.gov.hk/tc/career/edu/res
ource_teaching_kit.html (中文)
C.
1.
2.
3.
4.
Other Useful Websites
Royal Society of Chemistry – Problem based practical activities (https://edu.rsc.org/resources/problem-based-practicalactivities/939.article)
Royal Society of Chemistry Channel in YouTube (http://www.youtube.com/user/wwwRSCorg)
Royal Society of Chemistry - Screen experiments (https://virtual.edu.rsc.org/)
CLEAPSS Channel in YouTube (http://www.youtube.com/user/CLEAPSS)
2024-2025
Chemistry
SBA Teachers’ Conference
(26 Oct 2024)
1
Important remarks in
Chemistry SBA Teachers’ Handbook
https://www.hkeaa.edu.hk/en/sba/sba_hkdse_elective/dse_subject. html?7&2
Before submitting the SBA marks online, students
should be informed of the marks awarded and that
these marks are also subject to moderation by the
HKEAA. (Paragraph 3.1 & Appendix A)
2
Important remarks in
Chemistry SBA Teachers’ Handbook (cont’d)
Use of Artificial Intelligence (AI) tools in SBA
(Ch 3.3, Ch 6 )
Students should know:
Used properly, AI tools can offer new opportunities in
learning
However, overreliance and misuse of AI tools will diminish
the authentic learning opportunities
And AI tools have their shortcomings
Using an AI tool to gain an undue advantage is a malpractice
and can have serious consequences
Use of AI tools in SBA must be properly acknowledged
3
Important remarks in
Chemistry SBA Teachers’ Handbook (cont’d)
Student Declaration Form (Appendix E)
This form should be signed by senior secondary students at
the beginning of each school year in which SBA is undertaken.
Only one form needs to be completed by each student.
4
SBA Arrangement
& Requirements
5
SBA work schedule in 2024-25
Month / Year
Events
26 Oct 2024
SBA Teachers’ Conference
Sep 2024 –
May 2025
• Group meetings & school visits by District Coordinators
• S6 and S5 SBA activities to be conducted by schools
15 Jan–10 Feb Online submission of S5 and S6 SBA marks, Samples of
2025
students’ work and ‘List of S5 and S6 Experiments for 2025
Exam’ to the SBA System of HKEAA
March – May
2025
Moderation of S6 SBA marks by HKEAA
May – June
2025
S5 teachers to email ‘List of S5 Experiments for 2026 Exam’
to District Coordinators
July 2025
Release of 2025 HKDSE Examination Results
October 2025
Provision of feedback on the outcome of the SBA
moderation of 2025 HKDSE to schools
6
2025 onwards
Chemistry SBA
 Resume normal arrangement
7
S5 + S6
(2025 Exam)
Requirements
8
Assessment Requirement
School
Year
S5
S6
Chemistry
Minimum number of
assessment marks
Subject
weighting
2
2
10%
10%
 Over the two years of S5 and S6, there should be at least one mark for
Volumetric Analysis (VA), one mark for Qualitative Analysis (QA) and
two marks for Other Experiments (EXPT).
At least: 1VA + 1QA + 2 EXPT
 Investigative Study (IS) can be done in lieu of Other Experiments (EXPT).
In this case, one mark on ‘planning’ and one mark on ‘process and
reporting’ should be awarded. These two marks can satisfy the minimum
requirement for Other Experiments (EXPT).
9
SBA Framework (Handbook p.6)
10
On-line Mark Submission Screen
S5 (10%)
Student Name
V
V
Q
(Note: V= VA, Q = QA, E = EXPT)
Q
S6 (10%)
E
E
V
Q
E
E
E
E
(Note : maximum mark per task : 10)
11
 School-based Assessment System (SBAS) checks:
At least any 2 marks per student in S5
At least any 2 marks per student in S6
At least 1V, 1Q, 2E per student in S5+S6
12
School-based Assessment System (SBAS)
S5 + S6 Submissions
(2025 Exam)
13
What to submit
S5 and S6 Marks
Student Work samples
S5 and S6 Experiment Lists (Teacher document)
14
When to submit
• 15 Jan – 10 Feb 2025
•
SBA Marks, Student Work and Teacher Document
(Expt. Lists) are submitted in the same period.
•
Please submit SBA marks to the school principal for
endorsement in advance to allow sufficient time for
completion of other submissions.
15
Points to note before submission
Formal approval from HKEAA is required for
exemption of SBA marks.
If a student has fulfilled the minimum
requirements, exemption is not required.
No need to enter any symbol in the respective
mark cell(s).
Teachers may enter special symbols:
E = Exemption;
F = Fail to submit/perform;
P = Serious plagiarism
16
Hong Kong Diploma of Secondary Education
School-based Assessment System (SBAS)
Operation Guide
17
Overview of the SBA submission process
School
Administrator
Subject
Panel
(1st stage)
• Create/Update • Create teaching
groups
login accounts
for teachers and • Assign students
panels
to teaching
• Indicate the SBA groups
subjects being
• Assign teachers
offered in this
to teaching
school year
groups
• Assign SBA
subjects to
panels and
teachers
Subject
Teacher
Subject
Panel
(2nd stage)
Subject
Principal
Panel
(Last stage)
• Endorse SBA
• Upload Student
• Input SBA marks • Endorse SBA
marks submitted
marks for all
Work of all
(online input or
subjects
selected
by all teachers of
batch input
students
a subject
using the mark
• If necessary,
template)
return to panel • Upload Teacher
• If necessary,
to handle
Document if
• Endorse SBA
return to teacher
marks of
for amendments • Submit SBA
required
responsible
• Submit SBA
Marks to HKEAA
teaching
Marks to
group(s)
Principal
• Submit SBA
Marks to Panel
18
Submission of students’ work
Only student work with marks submitted to
HKEAA are required.
The work for each student should be zipped
to one single file if the work contains more
than one file.
The system accepts file formats, including
zip, pdf, txt, docx, rtf, ppt, pptx, xlsx, csv,
mp4, mp3, mpg, wmv, avi, etc.
19
Submission of students’ work (cont’d)
Uploading space allowed for each student’s
work:
15 MB
20
Submission of students’ work (cont’d)
Suggested file naming convention:
[Subject Abbreviation] [(6-digit Student Document Number)].[File extension]
e.g. CHEM(123456).zip
CHEM(246800).doc
CHEM(362880).pdf
Student Document Number is the beginning 6 digits
of the identity document of a student.
21
Submission of students’ work (cont’d)
If scanning is needed, advise students to use A4 paper
to do their homework and avoid faint handwritings
using pencils or light-green pens
If one or two reports were lost, mark in the first page
of the student work file, e.g. Chan Tai Man has lost
report #2 and #5.
Attach details of experiments /questions/guidelines /
mark-grade conversion table with the student work file
for the convenience of checking by District
Coordinators.
22
Request for a change of student(s) for
work submission
If the work of any chosen student cannot be located, or
involves any irregularities (such as mark penalty being
imposed due to partial plagiarism or late submission), the
Subject Panel should contact the SBA Team at 3628 8068.
Subject Panel should download the ‘Record/Change of
SBA Student Work Submission’ form from ‘Mark Reports’
under ‘Reports’ menu.
2024 – Chemistry
化學
23
Request for a change of student(s) for
work submission (cont’d)
24
Request for a change of student(s) for
work submission (cont’d)
Complete the section for the school and email/fax the
form to the HKEAA.
After confirming the arrangement, the HKEAA will
email/fax the amended form to the school for school’s
record.
25
Submission of Teacher Document
Teacher Document for Chemistry, means
S5+S6 List of Experiments performed.
Please make use of the template provided at
HKEAA website
26
List of Experiments (Template)
27
List of Experiments
 Include BOTH SBA & non-SBA experiments
 Indicate types of SBA tasks (VA, QA, EXPT)
correctly
 Not too simple titles of the SBA tasks
 Not too narrow range of topics covered in
the experiments
28
SBA for students with
Special Educational Needs
(SEN)
29
• Accommodation
• Exemption
30
31
•
providing ancillary aids and special assistance
e.g. assigning a technician / classmate / teacher to
tell the student about the colour of the solution
during titration
•
providing longer preparation / assessment time
•
providing alternative task (but same level of
difficulty) and perform a FAIR assessment (e.g.
making reference to School’s SEN policy, soliciting
advice from school management / Psychologist /
Therapist)
32
HKEAA website (https://www.hkeaa.edu.hk)
 School-based Assessment (Quick links)
 SBA System (Quick Links)
 Application for Exemption for School-based Assessment (SBA)
33
34
35
Reminder:
• Explain to the students the accommodation, or
why no accommodation is necessary
• Mark in the student work the kind of
accommodation or exemption involved if being
selected to be submitted to the HKEAA
36
SBA Teachers’ Handbook (Ch.4.3)
37
•
Call HKEAA SBA Team for logistical
arrangements (36288064)
38
SBA
Support Measures
39
Information on SBA Booklet
https://www.hkeaa.edu.hk/DocLibrary/Media/Leaflets/SBA_
booklet_eng.pdf
SBA information for students
40
Handbook for School Leaders on
School-based Assessment
HKEAA website (https://www.hkeaa.edu.hk)
 School-based Assessment (Quick Links)
 Subject Information on SBA
 General Information
 Handbook for School Leaders on SBA
41
Arrangements for SEN students in
SBA (For Schools, Parents and Students)
HKEAA website (https://www.hkeaa.edu.hk)
 School-based Assessment (Quick Links)
 Information Corners
 Arrangement for SEN students in HKDSE SBA
(For Schools, Parents & Students)
42
School-based Assessment System
(SBAS) Operation Guide
HKEAA website (https://www.hkeaa.edu.hk)
 School-based Assessment (Quick links)
 SBA System (Quick Links)
 School-based Assessment System Operation Guide
43
User Manual of SBA System
HKEAA website (https://www.hkeaa.edu.hk)
 School-based Assessment (Quick links)
 SBA System (Quick Links)
 User Manual of SBA System
44
Chemistry SBA Sample Tasks
HKEAA website (https://www.hkeaa.edu.hk)
 School-based Assessment (Quick Links)
 Subject Information on SBA
 Chemistry
 SBA Sample Tasks
45
List of Experiments (Template)
HKEAA website (https://www.hkeaa.edu.hk)
 School-based Assessment (Quick Links)
 Subject Information on SBA
 Chemistry  Forms  List of Experiments
46
SBA Mark Template
HKEAA website (https://www.hkeaa.edu.hk)
 School-based Assessment (Quick Links)
 Forms
 SBA Mark Templates
47
Reminder:
• Discuss with your District Coordinator (DC)
for subject-related questions
• Contact the SBA Team of the HKEAA for
questions related to logistical arrangements
48
Briefing Session on the SBA System(SBAS),
Technical Workshop on the SBA System
(optional) (for all subjects with SBA)
Date: Jan 2025 (tentative)
 Support measures for teachers with the mark
submission
 Practice using the SBAS to process simulated
SBA marks
 Technical assistance provided on spot
Details: school letter by HKEAA
49
Group Meetings / School visits
Date : Nov 2024 – May 2025
Interactive sharing on SBA implementation and
resources between DCs and group teachers
DCs will send email about the details
• School administrators need to update the contact
information of teachers in October on ‘School Information
Management System’ platform on HKEAA website
(as indicated in the school letter issued by HKEAA in mid Sept)
50
Enquiry Hotlines
General Issues:
3628-8860
3628-8070
SBA Team:
3628-8068
3628-8064
51
Thank you
52
HKDSE
Chemistry SBA Teachers Conference
Supervisor Remarks
October 2024
1
Supervisors’ Remarks
12 329 students (445 schools) submitted SBA marks
Moderation (statistical methods and professional judgment)
51.7% of schools within expected range
31.5% of schools higher than expected
16.8% of schools lower than expected
For those higher or lower than expected, majority only deviate
slightly from expected range
2
HKDSE 2025 Chemistry
[ ] 2022/2023 s.y.: S4 (No SBA)
[ ] 2023/2024 s.y.: S5 (at least 2)
[ ] 2024/2025 s.y.: S6 (total at least 4)
HKDSE 2026 Chemistry
[ ] 2023/2024 s.y.: S4 (No SBA)
[ ] 2024/2025 s.y.: S5 (at least 2)
[ ] 2025/2026 s.y.: S6 (total at least 4)
SBA Teachers' Handbook:
https://www.hkeaa.edu.hk/en/sba/sba_hkdse_elective/dse_subject.html?7&2
3
Learning, Teaching and Assessment in
SBA (1)
• Sufficient but not excessive learning opportunities
(appropriate number of exercises before
assessment)
• Feedbacks for enhancing learning
• Requirement: For the two years of S5 and S6,
conduct
(a) FOUR (4) SBA tasks and
(b) a minimum number of EIGHT (8) practical
work for Chemistry is stipulated
4
Learning, Teaching and Assessment in
SBA (1)
[SBA Teachers' Handbook, p.5, para. 2.2(a)]
5
Learning, Teaching and Assessment in
SBA (2)
• Fairness / Authenticity
• Attitudes marks are NOT required / will not be
accepted
• Appropriate support for students with special
educational needs
6
HKDSE 2025 SBA Requirements:
(SBA Teachers’ Handbook)
7
Assessment Requirement (2025)
Chemistry
School
Minimum number of
Year
assessment marks
S5
S6
2
2
Subject
weighting
10%
10%
 Over the two years of S5 and S6, there should be at least one mark for
Volumetric Analysis (VA), one mark for Qualitative Analysis (QA) and
two marks for Other Experiments (EXPT).
1VA + 1QA + 2 EXPT
 Investigative Study (IS) can be done in lieu of Other Experiments (EXPT).
In this case, one mark on ‘planning’ and one mark on ‘process and
reporting’ should be awarded. These two marks can satisfy the minimum
requirement for Other Experiments (EXPT).
8
On-line Mark Submission Screen --- 2025
S5 (10%)
Student Name
V
V
(Note: V= VA, Q = QA, E = EXPT)
Q
Q
S6 (10%)
E
E
V
Q
E
E
E
E
(Note : maximum mark per task : 10)
9
On-line Mark Submission Screen --- Examples
S5 (10%)
V
V
Q
Q
S6 (10%)
E
E
V
Q
E
8
8
9
7
8
9
9
8
Student 1
9
Student 2
8
Student 3
8
9
7
9
8
Student 4
9
9
7
9
8
8
Student 5
Student 6
8
9
7
(Note: V= VA, Q = QA, E = EXPT)
E
E

X
6
X
7
7
E
9
6
7
9
(Note : maximum mark per task : 10)


7
X
10
Type of Assessment Tasks:
 V.A. – for training and assessing basic skills for volumetric
•
analysis (Individual Task)
Assessment Criteria:
(a) The number of accurate titration readings is adequate and there
is an inclusion of the trial run.
(b) There is an accurate detection / recording of colour change.
(c) Calculations are shown clearly and concisely.
 Q.A. – for training and assessing of thinking skills, simple tests
on cations, and/or anions (Individual Task)
Note:
• Scope and depth of Q.A.: need NOT be similar to those of
the AL Chemistry Practical Examination.
• Should NOT include experiments like “identification of
functional groups of some organic compounds”.
11
Type of Assessment Tasks:
 EXPT - similar to those suggested in the Curriculum and
Assessment Guide CAG (Group Task)
• For ‘Chemistry’, they should be other than V.A. and Q.A.
• EXPT can be selected from the following topics:
‘Redox reaction', Chemistry reactions and energy’, ‘Rate of reaction’,
‘Chemical equilibrium’, ‘Organic synthesis’, ‘Analytical chemistry’ etc.
[SBA Teachers' Handbook, p.7, para. 2.4]
12
• EXPT – some examples from CAG
• building physical or computer models of addition polymers.
• performing experiments to investigate the typical reactions of
alkanes and alkenes.
• investigating the evaporation rates of substances with different
intermolecular forces.
• performing experiments to investigate redox reactions with common
oxidising and reducing agents.
• designing and performing electroplating experiments
• performing experiments to determine the enthalpy change of
formation of metal oxides or metal carbonates
• investigating the effect of changes in concentration of reactant /
temperature / surface area / the use of catalyst on reaction rate
• investigating the equilibrium of
to study the shift of equilibrium positions upon changing
concentration or temperature.
13
Student Written Works:
• Worksheet, quiz and brief report / detailed
report, etc. are all acceptable.
• Writing detailed laboratory reports is definitely a
good training.
Teacher Feedbacks:
• For facilitating students’ improvement
• To encourage students to reflect on / discuss with
teachers to understand their own strengths and
areas for improvement.
14
Students can be assessed:
• By worksheet, quiz and brief report / detailed
report, etc.: Basic Requirement
• By performance in carrying out experiments:
Optional, recommended if deemed
appropriate, but the related marks should be
indicated clearly on the submitted students’
written works (see the following example).
• But NOT by attitude
15
 Written work as the main
assessment tool, if
performance assessment
is used, allocate no more
than 20% of the overall
mark.
 Please include an
assessment rubric.
16
Marks vs Grades
• Marks (10, 9, 8, …1):
Preferred / Recommended
• Grades (A, B, C, … ):
Acceptable
• Teachers need to have a
well-defined mark-grade
conversion tables
17
• Some observations in previous years for deliberations:
• Narrow mark distribution within a class
• Some extreme cases, most students got very high marks
or most students got very low marks
Recommendations:
• Use marking guidelines / marking schemes
• Teachers may modify the task requirements / worksheet
items according to the general abilities of the students
in a class, for example,
• add some challenging items for classes of more able
students, or
• introduce some straight forward items for classes of
less able / less motivated students.
18
Recommendations (cont'd):
• Teachers may provide more written tasks in the
experimental handouts, for example, provide students with
• details of the experiment, such as aim and procedure,
and then request students to perform data analysis and to
write "conclusion" (for less proficient / able / motivated
students).
• procedure of the experiment, and request students to
complete their reports (for more proficient / able /
motivated students).
• brief outline of the experiment, and request students to
design the procedure and complete their reports (for
highly proficient / able / motivated students)
19
Recommendations (continue):
• Teachers can use worksheets from textbooks or tasks
provided by publishers, but ensure the students cannot
obtain the standard/reference answers before the SBA
assessment. Teachers are recommended to
• modify the standard worksheets
• use other means to enhance validity and reliability
• Teachers can use quizzes (“SBA Quiz”), but the
assessment items should closely related to a
performed experiment.
20
Recommendations (continue):
• Teachers could review assessment tasks to be used
with reference to
• Time available: half-day schooling, whole-day
schooling and other considerations
• Working space: working area of island benches /
side benches in school laboratory
• Task: time required / level of challenges / abilities
of students / individual and group based where
appropriate
21
For schools with more than one
chemistry classes:
• Teachers should perform within-school
standardisation, to standardise the SBA
tasks and marking standards.
• Students in a school should be assessed
on tasks of similar nature and
complexity, and call for similar skills.
22
Experiment List
• Please use the template provided
• Teachers may use their own format, but please include
sufficient details / descriptions for communication
• Include all the experiments performed, not only those
assessed.
List of experiments performed in F.5 Chemistry
Experiment 1 Cracking of paraffin oil
Experiment 2 Redox titration
Experiment 3 To determine the molarity of iron(II) sulphate solution (SBA)
Experiment 4 Effect of concentration on preferential discharge of ions
Experiment 5 To determine the Avogadro constant by electrolysis (SBA)
Experiment 6 Enthalpy change of reaction
23
Avoid (1)
• Late submissions
• Incomplete list e.g. only titles of assessed
experiments, include all experiments
performed in the list
• Uninformative experiment titles
• E.g. QA01, VA01, EXPT05
(Not good for communication)
24
Avoid (2)
• Missing reports
• Missing pages in the scanned PDF file, e.g. all even
pages were missing
• Only students’ answers on the worksheet, without
details of experiments
• Advise your students to avoid faint handwritings
e.g. pencils / light-green pens
25
Experience Sharing
and Suggestions
26
Special Case:
• SBA system:
• Michael Wong (9/10) and Mike Wong (6/10)
• Reports:
• Mike Wong (9/10) and Michael Wong (6/10)
• Suggestion:
• Ask your students always to use their full names
• Wong Kam Fai Michael and Wong Kar Fai Mike
• Double check the marks before submission
27
實驗報告 (1 5)
課程及評估指
：
學生應學習 ：
……
f.
涉及酸
(課程要求)
鹼的容量分析
• 標準溶液
• 酸鹼滴定
學生應能：
……
撰寫實驗報告將容量分析實驗的步驟
議學與教活動：
結果表達出來
28
實驗報告 (2 5)
(建議)
29
實驗報告 (3 5)
(建議)
30
(建議)
實驗報告 (4 5)
漸進推展方式：
(0) (1) 完整報告
（中４下學期及中５上學期）
(2) (3) （中５上學期）
（中５下學期或中６上學期）
31
(要求)
實驗報告 (5 5)
注意事項：
1) VA 或 QA：[ 本工作
] 作為SBA
課業呈交 HKEAA; [ 實驗報告 ] 可作
為練習。
2) EXPT：[ 本工作
、簡單或完整
報告] 作為 SBA 課業呈交 HKEAA。
32
Acid-base Titration: Citric Acid and dilute NaOH(aq)
Acidic
Close to the end Right after the
point
end point
Thymol blue
百里酚藍
33
Acid-base Titration: Citric Acid and dilute NaOH(aq)
Version 1
• You were given X g sample of pure solid citric acid (a
tribasic acid, formula mass 192.124). The sample was
dissolved in distilled water and make up to 25.0 mL.
• The diluted citric acid was titrated against a 0.0975 M
NaOH(aq) using thymol blue indicator. An average
volume of 22.6 mL NaOH(aq) was required to reach the
end point.
• What is X?
34
Acid-base Titration: Citric Acid and dilute NaOH(aq)
Version 2
• You were given 1.431 g impure sample of citric acid solid (a
tribasic acid, formula mass 192.124). The sample was
dissolved in distilled water and make up to 250.0 mL.
• A 25.0 mL sample of the diluted citric acid was titrated
against a 0.0975 M standardised NaOH(aq) using thymol
blue indicator. The results are shown below.
Initial Reading / cm3
Final Reading / cm3
Trial
First
Second
Third
0
23
1.2
23.7
2.0
24.7
1.4
24.0
• Determine the percentage purity of the given citric acid
sample.
35
Acid-base Titration: Citric Acid and dilute NaOH(aq)
Version 2
Post-lab Assessment Question:
A sample of 0.86 g solid (tribasic) citric acid C6H8O7
was titrated against a 0.50 M standardised NaOH(aq)
using thymol blue indicator.
The results are shown below. An average volume of
19.8 mL of NaOH(aq) was required. Determine the
percentage purity of the given citric acid sample.
(Relative atomic mass: H=1.0, C=12.0, O=16.0)
36
Problem: Citric acid content in a sweet and sour candy
Version 3
• To determine the citric acid content in a brand of sweet
and sour candies using the following reagents and
apparatus.
•
•
•
•
•
•
•
•
•
•
•
•
About 5.5 g sample of sweet and sour candies (hard) x2 or
about 8.5 g sample of sweet and sour candies (soft) x2
100 mL 0.010 M standardised NaOH(aq)
Thymol blue indicator in a dropping bottle
150 or 250 mL conical flask x2
250 mL volumetric flask x1
150 or 250 mL beaker x2
Burette x1
10 mL Pipette x1
Distilled water
Scissors x1
Mortar and pestle
37
Magnetic stirrer and bar
Results:
Hard Candies:
Average volume of 0.010 M NaOH(aq)
= (22.4 + 22.3) / 2
per 25.0 mL sweet and sour candies solution
(Prepared by adding 5.37 g of sweet and sour candies to
100.0 mL distilled water, then stirred vigorously for 30 minutes)
Soft Candies:
Average volume of 0.010 M NaOH(aq)
= (19.2 + 19.8 + 20.2) / 3
per 10.0 mL sweet and sour candies solution
(Prepared by adding 8.49 g of sweet and sour candies to
100.0 mL distilled water, then stirred vigorously for 30 minutes)
38
某品牌甜酸糖 A brand Sweet and Sour Candy
• 成分：糖、葡萄糖、糖漿、葡萄糖 (10%) 、酸（檸檬酸）、色
素（薑黃根提取物），食用香料，水果濃縮汁（橙子、酸橙和
檸檬）、維生素C。
• Ingredients: Sugar, Glucose, Syrup, Dextrose (10%), Acid
(Citric Acid), Colour (Turmeric Root Extract), Flavouring,
Fruit Juice Concentrate (Orange, Lime and Lemon),
Vitamin C.
• 淨重：50克 / 1.8安士
• Net Weight : 50 g / 1.8 oz
39
總結：檸檬酸
量實驗
測定巿售檸檬
含量
、巿售水壺除垢劑、甜
(Knowledge and skills: standard solution, acid base titration, problem
solving, observation, mole calculation, …)
巿售檸檬酸
巿售水
除垢劑
糖中的檸檬
甜酸糖
40
多謝
41
Sophia CHENG
RESOURCES ON CHEMISTRY PRACTICALS
Science Education Section
Education Bureau
https://www.edb.gov.hk/en/curriculumdevelopment/kla/science-edu/ref-andresources/chemistry.html
2
PLATFORM OF TEACHER RESOURCES ON SENIOR
SECONDARY CHEMISTRY
https://cd1.edb.hkedcity.net/cd/science/chemistr
y/teacher_resources/index.html
Please bookmark this page and subscribe to get our update notifications!
resource book for sixth-form practical chemistry
(12 experiments)
rbfsfpc12
4
WHY CHEMISTRY PRACTICAL
 fulfill assessment requirements (SBA)
 complement learning and teaching
 make learning chemistry more
meaningful and fun
5
INVESTIGATION ON THE EFFECT OF SUNLIGHT ON
BLEACH DEGRADATION
• Sodium hypochlorite (NaOCl) decomposes to form oxygen or chlorate when
exposed to sunlight
• Compare the OCl-(aq) concentration in bleach samples with and without
sunlight exposure
6
OCl-(aq) + 2H+(aq) + 2I-(aq)  I2(aq) + Cl-(aq) + H2O(l)
diluted bleach sample
excess
Starch as indicator
I2(aq)
+
2I-(aq) +
2S2O32- (aq)
S4O62-(aq)
standard sodium thiosulphate
Bleach sample
Volume of Na2S2O3 (aq)
required / cm3
Concentration of NaOCl (aq)
/ mol dm-3
Stored in
original
bottle
(for reference)
9.95
Without
exposure to
sunlight
Exposed to
sunlight
8.85
3.75
0.622
0.553
0.234
7
INVESTIGATION ON THE EFFECT OF SUNLIGHT ON
BLEACH DEGRADATION

Sunlight can speed up the decomposition of sodium hypochlorite
in bleach and significantly reduce its concentration, in turn
diminish its effectiveness as a disinfectant and a bleaching
agent.

Bleach should be contained in dark-colored or opaque
containers and stored in shaded cool place to prevent
decomposition induced by sunlight and high temperature.
8
INQUIRY-BASED EXPERIMENTS TO FURTHER INVESTIGATE BLEACH
DEGRADATION
By exploring variables:
 durations of sunlight
 temperatures
 different brands of bleach
Key components of inquiry-based experiments
 identify questions to study and make predictions
 conduct risk assessment
 decide on appropriate data table to show data
 suggest ways to improve validity and/or reliability of experiments
9
DETERMINATION OF ENTHALPY CHANGE OF NEUTRALISATION
2019 HKDSE Chem
Paper 1B
10 Q8
ACID-BASE VOLUMETRIC ANALYSIS USING THERMOMETRIC METHODS &
DETERMINATION OF ENTHALPY CHANGE OF NEUTRALISATION
Objectives:
1. To determine the concentration of NaOH(aq) via thermometric methods using a 1.0 M HCl(aq)
2. To calculate the enthalpy change of neutralisation (∆Hneut) between NaOH(aq) and HCl(aq)
Methods:
Two thermometric methods:
I.
Recording temperature changes when mixing acid and base in different volume ratios
II.
Recording temperature changes during an acid-base titration (no acid-base indicator)
The pros and cons of the two thermometric methods are compared and discussed.
Objectives
1. To determine the concentration of NaOH(aq) via thermometric methods using a 1.0 M HCl(aq)
2. To calculate the enthalpy change of neutralisation (∆Hneut) between NaOH(aq) and HCl(aq)
Method 1:
Method 2:
Set-up
A
B
C
D
E
F
G
Volume of HCl(aq) / cm3
10
15
20
25
30
35
40
Volume of NaOH(aq) / cm3
40
35
30
25
20
15
10
1.0 M HCl in the burette
25 cm3 NaOH in the polystyrene cup
METHOD 1
Set-up
A
B
C
D
E
F
G
Volume of HCl(aq) / cm3
10
15
20
25
30
35
40
Volume of NaOH(aq) / cm3
40
35
30
25
20
15
10
Method 1 (Mixing):
After calculations:
Max: 7.0 oC
HCl: 24.80 cm3
NaOH(aq) = 0.98 mol dm-3
∆Hneut = -58.99 kJ mol-1
Actual values:
NaOH(aq) = 0.85 mol dm-3
∆Hneut = -57.62 kJ mol-1
METHOD 2 – THERMOMETRIC TITRATION
After calculations:
Max: 30.5 – 25.0 = 5.5 oC
HCl: 22.60 cm3
NaOH(aq) = 0.90 mol dm-3
∆Hneut = -48.42 kJ mol-1
Actual values:
NaOH(aq) = 0.85 mol dm-3
∆Hneut = -57.62 kJmol-1
COMPARING METHOD 1 AND METHOD 2
Accuracy of results:
Concentration of NaOH
Method 1
(Mixing)
Method 2
(Titration)
∆Hneut
Pros
Cons
Method 1
(Mixing)
Better temperature control /
Less heat loss
Less accurate volume
measurement
Method 2
(Titration)
More accurate volume
measurement for estimating
equivalence point
Significant heat loss
WRITING A LABORATORY REPORT
Topic IV Acids and Bases
Volumetric analysis – Determining the concentration of hydrochloric acid
Pre-lab Assignment
Information of the experiment:
Carry out volumetric analysis using 0.025 M sodium carbonate solution,
hydrochloric acid with unknown concentration, and an acid-base indicator.
Determine the concentration of the hydrochloric acid.
Method:
1. Dilute 25.00 cm3 of the given hydrochloric acid to 250.00 cm3 with distilled
water.
2. Titrate 25.00 cm3 of the diluted hydrochloric acid against 0.025 M sodium
carbonate solution, using a suitable acid-base indicator.
16
VOLUMETRIC ANALYSIS – PRE-LAB ASSIGNMENT
Task:
Write the experimental procedure as detailed as possible and plan ahead the result
recording and data analysis to be carried out. This handout will be your sole
reference during the experiment in the coming practical lesson.
Pre-lab:
1. Objective of the experiment
2. Chemicals, materials and
apparatus
3. Safety precautions
4. Procedure
5. Chemical equation and result
table
Practical part:
1. Conducting VA experiment
2. Carrying out data
analysis
3. Answering discussion
question(s)
Detailed lab report:
1. Re-write procedures
with past passive tense
2. Combining pre-lab
worksheet with data
analyses and discussion
to form a complete lab
report
17
CONTACT INFORMATION
Science Education Section, Curriculum Support Division, EDB
Dr CHENG Siu-lin, Sophia
Tel: 3698 3436
Email: sophiaslcheng@edb.gov.hk
Ms CHAN Wai-long, Phoenix
Tel: 3698 3439
Email: chanwailong@edb.gov.hk
Dr LI Tin-lok, Matthew
Tel: 3698 3447
Email: matthewtlli@edb.gov.hk
18
THANK YOU!