Kirkcaldy High School - Chemistry Higher Assignment Pupil
Guide
Name: ______________ Class: _____
Antioxidants
This assignment is worth 20% of the overall marks for the
Higher course assessment. The course is graded A-D.
In this assignment, you will have to investigate a relevant topic in chemistry and communicate your research
in a report. The topic must have an application with an effect on the environment/society.
Your report must be completed independently.
The assignment has two stages
research stage
communication stage
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Guidance on Producing your Report
Your report should have:
• Appropriate structure with an informative title and headings where necessary
• Be clear and concise
Aim
The aim must describe clearly the question you are trying to answer.
Introduction and Underlying Chemistry
Here you must describe the uses of antioxidants.
You should explain the underlying chemistry of antioxidants. You should include the definition of a fuel as
well as formulae, chemical equations and calculations. The Chemistry must be at Higher level.
Research – Data/Information
Here you must present two pieces of raw data/information taken unchanged from two sources that is
relevant to your investigation. One of these pieces of data must be from the experiment you have carried
out.
You must also process these two pieces of data. This can include, for example, performing calculations, and
plotting graphs from tables. One of your pieces of processed data must be a bar chart or line graph.
It must be clear where the raw data that you processed came from. For example you could:
• Include raw data from an experiment/practical activity
• Include tables, graphs, diagrams, text taken from your sources
• Explain clearly where the data/information came from (reference your sources)
On your bar chart/line graph. Check that you have included, as appropriate:
• Suitable scales
• Units
• Headings
• Labels
You should also compare and analyse the data from your sources. For example, describe how they
agree/disagree or describe other similarities/differences. You must comment on any trends and the “value”
of the trend (i.e. twice as much, three times as much etc.).
Risk Assessment
You must include a risk assessment for the experiment you carried out. This cannot be simply “safety glasses
were worn and hair was tied back”. You should comment on specific risks from the chemicals you used and
how you reduced that risk.
Conclusion
You must clearly state the conclusion(s) of your investigation. Your conclusion(s) must answer every point in
your aim and be supported by what the data from your sources.
Evaluation
You must evaluate your report, commenting on:
• robustness of findings
• validity of sources
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•
•
reliability of data/information
evaluation of (experimental) procedure
References
At the end of your report you must record the sources you have used, with enough detail to allow someone
else to find them. If one of the sources is an experiment/practical activity, then you need to include the title
and the aim. If you are including a reference, give the full web address including “http://”
You must explain your choice of sources in terms of the following:
• Relevance: how useful they are for your topic?
• Reliability of sources: who wrote them? Who published them?
Before submitting your report check you have completed the checklist at the back of this booklet to ensure
you have included everything.
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Antioxidants
An antioxidant is a molecule that inhibits the oxidation of other molecules. It could be said that antioxidants
“sacrifice” themselves in order to prevent other substances from being oxidised. Oxidation can happen due to
the creation of free radicals – atoms or molecules with unpaired electrons. Free radicals react according to
three processes. These are:
• Initiation: Where free radicals are created from non-radical species
• Propagation: Where free radicals react and produce further free radicals (chain reaction)
• Termination: Where free radicals combine to make non-radical species
For example, free radicals can be created in a sample of hydrogen and chlorine gasses using a flash light
source. This explosive reaction occurs as follows:
Initiation
H2 → 2H•
Cl2 → 2Cl•
Propagation
H• + Cl2→ HCl + Cl•
Cl• + H2→ HCl + H•
Termination
2H• → H2
2Cl• → Cl2
Overall
H2+Cl2 → HCl
Free radicals can be created in human skin due to exposure to ultra-violet light (sunlight). Because of this it is
often said that eating antioxidant-rich foods or by using antioxidant rich skin cream is good for you and can
help to slow down the aging process. Common antioxidants are vitamin C, vitamin E and β-Carotene.
vitamin E
β-Carotene
vitamin C
In order to test the antioxidant levels in a number of substances, you will titrate solutions with iodine. Say for
example, the antioxidant in the substance is vitamin C (ascorbic acid). It oxidises to dehydroascorbic acid as
follows.
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C6H8O(aq) → C6H6O6(aq)
This can be balanced to a full redox equation by adding 2 x H+ and 2 x e- on the right hand side thus showing
oxidation (loss of electrons):
C6H8O(aq) → C6H6O6(aq) + 2H+(aq) +2eThe corresponding reduction of iodine is:
I2 → 2IThis can be balanced to a full redox equation by adding 2 x e- on the left hand side thus showing reduction
(gain of electrons):
I2(aq) + 2e- → 2I-(aq)
These two half equations for oxidation and reduction can then be combined and the electrons cancelled:
C6H8O(aq)
I2(aq) + 2e-
→
→
C6H6O6(aq) + 2H+(aq) + 2e2I-(aq)
C6H8O(aq) + I2(aq)
→
C6H6O6(aq) + 2H+(aq) + 2I-(aq)
Using starch as an indicator, the endpoint is reached when the solution turns blue/black i.e. the iodine is no
longer reacting. Using this equation and an experimental result, the quantity of antioxidants in a sample could
be calculated as follows. Say that a 100 cm3 solution of 100 g of apple was made and 20 cm3 of this solution
reacted with 15 cm3 of 0.005 moll-1 iodine solution to reach the endpoint:
C6H8O(aq)
+
I2(aq) →
C6H6O6(aq)
+
2H+(aq)
+
2I-(aq)
N
0.000075
0.000075
-1
C (moll )
0.005
V (l)
0.02
0.015
CxV
niodine = nvit C =
=
0.005 x 0.015
=
0.000075 mol = 0.075 mmol
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Therefore in 100 cm of the solution there are 0.075 x 5 mmol = 0.375 mmol. So there are 0.375 mmol of
antioxidant per 100 g of apple.
Your investigation
Your aim is to answer the question “Which foods contain the greatest quantities of antioxidants?”
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Practical
This assignment has a practical associate with it. You should write this up separately to your final report but
you must include raw and processed data from the practical in your final report. You should reference your
experiment with the aim and title of the experiment.
Practical – Which foods contain the greatest quantities of
antioxidants?1
Apparatus
•
•
•
•
•
•
•
•
•
burette and stand
100 mL or 200 mL standard flask
20 mL pipette
10 mL and 100 mL measuring cylinders
250 mL conical flasks
Balance
Starch indicator solution
Iodine solution (0.005 moll-1 and 0.0005 moll-1)
Fruit/veg./tea etc.
Method
1. Cut a sample into small pieces and grind in a mortar and pestle or blend in a blender.
2. Add 10 cm3 portions of distilled water several times while grinding the sample, each time decanting off
the liquid extract into a 100 mL volumetric flask.
3. Strain the ground fruit/vegetable pulp through cheese cloth, rinsing the pulp with a few 10 cm3
portions of water and collecting all filtrate and washings in the standard flask.
4. Make the extracted solution up to 100 cm3 or 250 cm3 with distilled water.
5. Pipette a 20 cm3 aliquot of the sample solution into a 250 cm3 conical flask and add about 150 cm3 of
distilled water and 1 cm3 of starch indicator solution.
6. Titrate the sample with iodine solution. The endpoint of the titration is identified as the first
permanent trace of a dark blue-black colour due to the starch-iodine complex. If the titration
volume is too large (greater than 30 cm3 or less than 4 cm3) you may need to use an alternative
concentration of iodine solution.
7. Repeat the titration with further aliquots of sample solution until you obtain concordant results (titres
agreeing within 0.2 cm3).
1
http://www.chemteach.ac.nz/investigations/documents/vitaminc_iodine.pdf - with thanks!
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Experiment Log
Assessment Standard
1.1
Planning an
experiment or
practical
investigation
Evidence required
Aim of experiment
Evidence produced
Dependent and
independent
variables
Variable to be kept
constant
Measurements and
observations are
made
Resources
Method including
safety
1.2
Following
procedures
safely
Procedures have
been followed safely
and correctly
1.3
Making and
recording
observations
and
measurements
accurately
Presenting
results in an
appropriate
format
Observations and
measurements taken
are correct
1.5
Drawing valid
conclusions
What the experiment
shows, with
reference to the aim
1.6
Evaluating
experimental
procedures
The suggestion given
will improve the
experiment
1.4
Results have been
presented in an
appropriate format
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Final Report Log
Aim
1 mark
Research
worth 6
marks total
Category
Sub-category
describe clearly what you are investigating.
Selection of data
/ information
2 marks
Show raw data from two, or more, sources. - only one of these can
be an experiment.
(this can be made in advance and used in the final write up)
Make it clear where the data comes from
Processing
information
2 marks
‘Process the data’ from at least two sources – this can include
processing data you found into graphs or charts or diagrams (such
as converting tables to line graph. table into pie chart or calculate
averages from data you found or summarising text that you found
Presenting
information
The information that you processed should be presented in two
different formats:
2 marks
Summary
One must be a graph, table, chart or
Graph
diagram
Table
Chart
Diagram
Check that you have included, as appropriate:
Format 1
Experiment
Risk
Assessment
1 mark
Underlying
chemistry
4 marks
Risk assess your
experiment
Format 2
Suitable scales
Units
Headings
Labels
This cannot be simply “safety glasses were worn and hair was tied
back”. You should comment on specific risks from the chemicals
you used and how you reduced that risk.
How the
underlying
chemistry relates
to your topic.
Data is analysed
Include the chemical principles involved. Have one or more of
Formulae & or chemical equations
Structures
Calculations
Interpreting data included in the report (which may/may not have
been processed by the candidate) to identify relationships. This
may include further calculations.
Conclusion is supported by what you have found out. Answer your
original aim completely.
Evaluation
3 marks
Your
conclusion(s)
relates to aim
Evaluate your
report
Presentation
2 marks
Appropriate
presentation
Analyse
data/inform
ation
2 marks
Conclusion
1 mark
Comment on:
• robustness of findings
• validity of sources
• reliability of data/information
• evaluation of (experimental) procedure
1 mark for each of:
• appropriate title and structure
• the references to at least two sources used in the report
are given in sufficient detail to allow them to be retrieved
by a third party — to reference the experiment/practical
activity, then the title and the aim should be recorded
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