BUJUUKO HIGH SCHOOL
UGANDA ADVANCED CERTIFICATE OF EDUCATION
COMPETENCE BASED ASSESSMENT
BEGINNING OF TERM 11 EXAMS 2025
S.5 CHEMISTRY PAPER 1
TIME 2 ½ Hours
NAME ……………………………………………………….. SIGN……....
INSRTUCTIONS
Attempt all items
A local pharmaceutical company is developing a new cough syrup. During quality
control, several organic compounds are detected as possible impurities. As part of
your internship with the quality assurance team, you are asked to identify and
name these compounds using IUPAC nomenclature.
You are provided with the following molecular structures (or condensed formulas),
and your task is to ensure they are correctly identified and named according to
IUPAC rules to avoid any dangerous mix-ups during drug formulation.
List of Detected Compounds (in condensed form):
1. CH₃CH₂CH(CH₃)CH₂CH₃
2. CH₃CH₂COOH
3. CH₃CH₂CH₂OH
4. CH₃COCH₂CH₃
5. ClCH₂CH₂CH₃
Task
(a) Identify and name each compound using IUPAC rules.
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(b) Which functional groups are present, and how do they affect naming and
numbering?
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. (c) One of the detected compounds has similar structure to a known narcotic.
How would you use structural information and IUPAC naming to distinguish
between a harmless and a harmful compound in a lab report?
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Item 2
You are part of a national science competition where your school has been tasked
with solving a mystery involving a malfunctioning industrial machine used in
metal processing. The machine separates metals based on their reactivity and
electronic configuration, but it has stopped working correctly due to a suspected
programming error in how it identifies elements.
Your team is given a list of six elements used in the machine’s sorting system:
Iron (Fe, 26)
Magnesium (Mg, 12)
Calcium (Ca, 20)
Manganese (Mn, 25)
Potassium (K, 19)
Zinc (Zn, 30) Task
(a) You must reprogram the machine to correctly sort these elements by
confirming their electronic configurations.
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(b) The machine accidentally classified manganese and zinc in the same
category. Based on their configurations, explain why this is incorrect
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(c) Suggest how the machine should differentiate elements with partially filled
d-orbitals from those with filled ones
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Item 3
A local government is launching a campaign to reduce the overuse of fertilizers in
farming. As part of a pilot study, a team of chemists analyzes the amount of
ammonium nitrate (NH₄NO₃) being used by farmers in a rural area.
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One farmer reports using 500 kg of ammonium nitrate per season. The chemists
want to understand the potential impact on the local water supply, since excess
nitrates can lead to eutrophication in nearby lakes.
Tasks:
(a) . Calculate the number of moles of ammonium nitrate in 500 kg.
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(b) Determine the number of nitrogen atoms delivered to the soil.
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(c) . Assuming 10% of the nitrate leaches into water systems, calculate how
many moles of nitrate ions enter the environment.
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(d) . Based on your results, discuss how chemistry can help address
environmental concerns related to fertilizer overuse
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SECTION B
ITEM 4
In a small rural town, local artisans and entrepreneurs are exploring ways to
produce alternative fuels and useful chemical products using available resources. A
team of young chemists is consulted to advise on the chemical processes and safety
implications of the following:
1. A community wants to produce ethene (a compound used to make
lightweight plastics) from ethanol using concentrated sulfuric acid.
2. A refrigeration technician reports the accidental release of chlorinated
propane derivatives after exposure of propane gas to sunlight in an area where
cleaning chemicals containing chlorine were being used.
3. A small-scale soap manufacturer considers using propene and halogens to
synthesize disinfectant additives.
4. The same manufacturer later realizes a dihalide compound is forming when
bromine water is added to propene and wants to know how it forms and whether it
is safe.
Task
As a consulting chemist, you are tasked with the following:
a) Analyze and write a chemical equation for each reaction implied in the
situations above.
b) Identify the type of reaction occurring in each case (e.g., elimination,
substitution, addition) and outline the complete reaction mechanism, stating all
required conditions.
c) Evaluate the potential risks and suggest safety or environmental
considerations for each process, especially in a rural or low-resource context.
d) Propose one sustainable alternative or improvement for any one of the
processes above that would reduce harm to people or the environment while still
meeting the community's goal ( 15 SCORES )
ITEM 5
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As the head of nuclear chemists department working at a medical research facility
developing radiopharmaceuticals for cancer diagnosis and treatment, your team is
evaluating two radioisotopes, Technetium-99m (Tc-99m) and Iodine-131 (I-131),
for use in diagnostic imaging and thyroid cancer therapy, respectively. You need to
analyse their radioactive properties, calculate quantities based on half-life, and
assess their suitability for medical applications to ensure patient safety and
treatment efficacy.
Tasks
a) Define radioactivity and explain how the half-life of a radioisotope is used to
determine the amount of radioactive material remaining after a given time.
b) Tc-99m has a half-life of 6.0 hours. If a hospital prepares a 200.0 mg sample of
Tc-99m for a diagnostic scan, calculate the mass of Tc-99m remaining after 18.0
hours. Show your work using the half-life formula or decay calculations.
c) I-131, used in thyroid cancer treatment, has a half-life of 8.0 days. If a patient is
administered 50.0 mg of I-131, determine how many days it will take for the mass
to decrease to 6.25 mg. Show your reasoning.
d) Discuss one medical application of Tc-99m in diagnostic imaging and one
application of I-131 in cancer therapy, explaining how their radioactive properties
make them suitable for these uses. Identify one challenge in using radioisotopes in
medicine and propose a strategy to address it.
e) A colleague suggests using Carbon-14 (C-14, half-life 5730 years) for a new
archaeological dating project at a nearby university. Explain how the mole concept
and half-life calculations could be applied to determine the age of a sample
containing C-14, and comment on whether C-14 would be suitable for medical
applications like those of Tc-99m or I-131.
Item 6
A rock sample from Maya quarrying site was picked by a worker and due to its
attractiveness, thought was gold. He picked more interest and submitted it to the
laboratory for analysis. It was later confirmed by the mineralogist that it was
magnesium oxide as;
Mass of crucible and lid; 50.00g
Mass of crucible, lid and magnesium; 50.24g,
Mass of crucible, lid and magnesium oxide; 50.40g
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Task
The worker who is also your guardian approaches you for guidance on how to
determine mass of magnesium, oxygen and formula of magnesium oxide. How
would you go about it? (Mg=24, O=16)
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