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E4: Investigating the UV-Vis
absorbance of sunscreens
On this page...
Introduction (https://canvas.sydney.edu.au/courses/41313/pages/e4-investigating-the-uv-vis-
absorbance-of-sunscreens#intro)
Safety Information (https://canvas.sydney.edu.au/courses/41313/pages/e4-investigating-the-
uv-vis-absorbance-of-sunscreens#safety)
Labtorial Resources (https://canvas.sydney.edu.au/courses/41313/pages/e4-investigating-
the-uv-vis-absorbance-of-sunscreens#labtorial)
Lab Manual (https://canvas.sydney.edu.au/courses/41313/pages/e4-investigating-the-uv-vis-
absorbance-of-sunscreens#manual)
"Dry Lab" Results (remote students only)
(https://canvas.sydney.edu.au/courses/41313/pages/e4-investigating-the-uv-vis-absorbance-of-
sunscreens#results)
Assessments (https://canvas.sydney.edu.au/courses/41313/pages/e4-investigating-the-uv-
vis-absorbance-of-sunscreens#assessments)
Introduction
The sun is a yellow dwarf star approximately 1.5 × 10 km distant from Earth.
The light emitted by the sun can be approximated as that of a black body with
a surface temperature of ~5250 °C, the temperature of its photosphere.
8
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Figure 1 - Solar spectrum
While this spectrum peaks in the visible, a significant proportion of the sun’s
radiation are emitted at ultraviolet (UV) wavelengths. This ionising radiation
has been known to cause skin cancers in humans, including the lethal
malignant melanoma. In 2005 there were 10,684 new cases of melanoma
diagnosed. In that same year, melanoma was responsible for 1272 deaths.
Scientists can be exposed to additional sources of UV radiation, including
ultraviolet lamps and UV lasers (such as Excimer lasers or frequency-doubled
lasers). Several such lamps and UV lasers are used in the School of
Chemistry.
Types of UV radiation:
Ultraviolet radiation is often broken up into 3 subtypes, based on its
wavelength and the risk that is posed.
UVA: 400 nm–315 nm: The least harmful subtype of UV. UVA reportedly
causes such adverse effects as loss of collagen, a decrease in the number of
blood vessels and alteration of connective tissue of the dermis. While
protection from UVA is desirable, it is not included in SPF ratings for
sunscreens.
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UVB: 315 nm–280 nm: This radiation is responsible for tanning and sunburn
and is the class of radiation most responsible for skin cancers.
UVC: 280 nm–100 nm: While this form of radiation is highly dangerous, it is
absorbed by the atmosphere and therefore poses a limited threat. Most UVC is
absorbed in the ozone layer, due to the photodissociation of ozone.
Therefore, in areas where the ozone layer has been depleted (such as at the
Earth’s poles) UVC can represent a serious hazard. In the late 20th Century,
as a direct result of the danger posed by UVC radiation, international
legislation was introduced controlling the use of ozone-depleting chemicals.
Sunscreens
The body’s natural defence against UV radiation is melanin, a complex
aromatic polymer synthesised in cells called melanocytes in response to UVB
radiation. It is a brown-black pigment that absorbs harmful UV radiation and
converts its energy into heat. To reduce the risk of skin cancer and sunburn,
many humans use protective clothing, glasses and chemical sunscreens whilst
in the sun. Sunscreens work in a similar fashion to melanin - they form a layer
above the skin which absorbs dangerous UV radiation. They are rated by a
sun protection factor, SPF.
where “minimal erythemal dose” (MED) is the length of time that one can stay in the sun before
getting sunburnt.
Safety Information
Hazard Identification and Risk Assessment
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Identify the
Hazard
Determine the
Risk
Control the Risk Disposal of
Waste
2-Propanol
Hazardous –
Flammable.
Moderate risk. Wash skin or eyes
immediately under water if
spill or splash occurs.
Avoid sources of ignition.
Place your
samples in the
residue
containers
provided.
Commercial
Sunscreens
Non-hazardous.
Low risk. N/A

Labtorial Resources
Worksheets
The following worksheets cover theory, concepts and calculations covered
experiment 1. You should watch the short video available to watch at the top of
each worksheet which will explain the theory and content covered in the
worksheet. The worksheets will unlock at 12:01 am Monday the week of your
labtorial and you then have 2 weeks to complete them. You have an unlimited
number of attempts within this 2 week period with your highest score be
counted. You must attempt and submit all 5 worksheets BEFORE your lab
class next week to be allowed to participate.
Labtorial Worksheet 4a - Spectroscopy
(https://canvas.sydney.edu.au/courses/41313/quizzes/182954)
Labtorial Worksheet 4b - Standard Solutions
(https://canvas.sydney.edu.au/courses/41313/quizzes/182948)
Labtorial Worksheet 4c - Calibration Curves
(https://canvas.sydney.edu.au/courses/41313/quizzes/182955)
Labtorial Worksheet 4d - Plotting
(https://canvas.sydney.edu.au/courses/41313/quizzes/182947)
Labtorial Worksheet 4e - The Experiment
(https://canvas.sydney.edu.au/courses/41313/quizzes/182953)
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Practical Exercises (On-Campus only)
The following exercises are not assessed and aim to give you practical
experience of the various laboratory techniques you will be using in next
week's experiment. It is an opportunity to learn and master the correct
technique without the pressure of affecting your lab experiment. These
practical labtorials will only run for 90 min with students being staggered over
the timetabled 3 hour lab session. Please check your personalised lab
schedule to see what time you should attend your practical labtorial lab class.
Note these exercises are only for on-campus students only.
Using the UV-Vis spectrophotometer and performing regression
analysis in Excel (https://canvas.sydney.edu.au/courses/41313/files/22568568?wrap=1)
(https://canvas.sydney.edu.au/courses/41313/files/22568568/download?download_frd=1)
Lab Manual/Experiment Details
On-Campus Lab Manual
(https://canvas.sydney.edu.au/courses/41313/files/22570983?wrap=1)
(https://canvas.sydney.edu.au/courses/41313/files/22570983/download?
download_frd=1)
"Dry Lab" Results (Remote students only)
Note that some variation from the lab manual may be observed. Where
present, follow the instructions provided in the following pages and videos.
Part one - UV Spectra of Sunscreens
(https://canvas.sydney.edu.au/courses/41313/pages/e4-investigating-the-uv-vis-
absorbance-of-sunscreens-part-1-of-4)
Part two - Concentration dependence
(https://canvas.sydney.edu.au/courses/41313/pages/e4-investigating-the-uv-vis-
absorbance-of-sunscreens-part-2-of-4)
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Part three - The case of the absent-minded technician
(https://canvas.sydney.edu.au/courses/41313/pages/e4-investigating-the-uv-vis-
absorbance-of-sunscreens-part-3-of-4)
Part four - Eye protection
(https://canvas.sydney.edu.au/courses/41313/pages/e4-investigating-the-uv-vis-
absorbance-of-sunscreens-part-4-of-4)
Assessments
Labtorial Worksheet (1%)
(https://canvas.sydney.edu.au/courses/41313/pages/e4-investigating-the-uv-vis-
absorbance-of-sunscreens#labtorial)
The labtorial worksheet covers theory, techniques, safety hazards and practice
calculations you will utilise in the subsequent experiment. For this reason,
the labtorial worksheet MUST be completed BEFORE you attend lab for this
experiment (or attempt your dry lab online for remote students). Note that
there is an unlimited number of attempts (until it closes) and full marks are not
required for lab access (just a submission attempt). The closing date is 11:59
pm Sunday after the experiment lab class so you still have time to discuss the
questions/content with your demonstrator and improve your mark if you are yet
to score full marks.
Logbook (1%) (https://canvas.sydney.edu.au/courses/41313/assignments/359924)
During the experiments, you are required to take notes of measurements and
observations. You will also be prompted by questions in the lab manual/dry lab
pages/demo slides. A marking guide will be provided for each experiment of
what to expect. An exemplar logbook is also provided
(https://canvas.sydney.edu.au/courses/41313/files/22045143/download?wrap=1)
(https://canvas.sydney.edu.au/courses/41313/files/22045143/download?
download_frd=1) .
Submit your logbook
(https://canvas.sydney.edu.au/courses/41313/assignments/359924) to CANVAS
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by the end of the week. This should either be a scan/photograph copy of your
hand-written logbook or a typed-up log book submission.
Marking Rubric
This logbook contributes 1% of your Unit of Study. The breakdown of marks
are as follows:
Criteria
Formatting
UV-Vis Spectra
UV-Vis Spectra Questions
1. Rate all the sunscreens on their ability to provide protection against UVA and UVB? Does
from the sun?
2. Which sunscreen(s) would offer the best protection in Antarctica? Why?
3. The laser spectroscopy lab in the Madsen Building has lasers with the following wavelengt
and 193 nm. Would any of the sunscreens provide protection for all these wavelengths fro
lasers?
Concentration Dependence Tables
of all 4 sunscreens
Concentration dependence graphs
of all 4 sunscreens
Concentration dependence questions
1. Using ONLY your samples giving an absorbance less than 1, perform a linear regression a
coefficient from the slope of this analysis.
2. The molar extinction coefficient is the measurement of how strongly a chemical species ab
is an intrinsic property of the species which allows us to directly compare species against o
stronger a species absorbs a particular wavelength. Compare the molar extinction coefficie
record down each of the extinction coefficients for all 4 of the sunscreens your group have
would you want a larger or lower absorption coefficient? Which one provides this?
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Criteria
Unknown Sample (Part 3)
Spectra & Discussion on eye protection

Major Post-lab Assessment Option 4 (of 4): Infographic
(10%)
($CANVAS_OBJECT_REFERENCE$/assignments/gc2e951da3e05348e697350ad0325dc42)
Indicate this assessment as your preference here.
(https://canvas.sydney.edu.au/courses/41313/quizzes/179532)
(https://canvas.sydney.edu.au/courses/41313/pages/e2-environmental-forensics#Letter)
Expected length: 1 page
You are to provide an infographic offering consumer advice on sunscreen to
the general public. An infographic is a collection of imagery, charts,
and minimal text that gives an easy-to-understand overview of a topic. The
main focus point will be around your ranking of sunscreens based on the molar
extinction coefficient (ie which sunscreens performed the best and worst in
your study?). You should also provide some information on how the ranking
was determined but remember this is for the general public so keep it simple it
and avoid getting too technical! You are free to add whatever other content
you deem relevant to your poster. The infographic will mainly be marked on
the flow of content, appropriateness to the target audience and its eye-catching
factor.
Marking Rubric
This post-lab assessment contributes 10% of your Unit of Study and is due
11:59 pm Sunday 15th May (End of week 11). The breakdown of marks are as
follows:
Criteria
2022/5/18 15:12 E4: Investigating the UV-Vis absorbance of sunscreens: CHEM1X11 Chemistry 1A - Lab Programme
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Criteria
Visual appeal
Creative elements that engage a viewer.
Not too busy. Neat and tidy,
Good colour scheme.
Word content
Perfect amount of words. Minimum amount to inform the viewer.
Message clarity
The topic and messages of the infographic are clear and easily understood; Intended
viewer.
Target Audience
The information is pitched with the right level for general public.
Relevance
A small piece/section that discusses the reason for this research, why it is important o
Data representation
Entire groups data is used. Data is accurately used and presented.
Communication of data
Data/results is presented in a simple and "easy to digest” (understand) manner.
Recommendation
Recommends or promotes one of the products tested based on results.
Grammar
Free of spelling and grammatical errors
Resources
The following resources may help you prepare your infographic:
How to
make/prepare
infographics
The different types
of infographics
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communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be
the subject of copyright protection under the Act. Do not remove this notice.
Live streamed classes in this unit may be recorded to enable students to review the content. If you have concerns about this, please
visit our student guide (https://canvas.sydney.edu.au/courses/4901/pages/zoom) and contact the unit coordinator.
How to M…

The 9 Typ…

Infographic Designing Websites
Note: you do not need to use these websites, they are simply extra resources
for you to use. Powerpoint is a great software for producing infographics also.
Some of these infographic websites will require payment for use of their
premium designs.
https://www.canva.com/infographics/templates/
(https://www.canva.com/infographics/templates/)
https://venngage.com/templates/infographics
(https://venngage.com/templates/infographics)