QuestionQuestion

Read about the UV Spectrum of Sunscreens. Then, answer the following questions:
Your report will consist of answers to the following questions.
1. Research has shown that the most effective wavelength for causing sunburn (erythema) is 296.7 nm. Longer wavelengths, particularly around 313 nm, are more effective in tanning. Evaluate each of your sunscreens and suntan lotions by measuring the intensity of absorption at these two wavelengths.
2. The fastest scanning speed of the instrument has the lowest resolution; it samples the fewest number of different wavelengths to measure the spectrum. Suppose that you were very interested in the structure of the spectrum – locating all of the maxima, shoulders, and other features. How would you choose the speed of the scan?
3. It turns out that acetone is much better at dissolving all of the sunscreens than absolute ethanol. Why did we not use acetone as a solvent?
4. Is there any relationship between the spf value and the intensity of absorption?
5. Why did we not continue our spectrum to wavelengths below 240 nm?
6. While UV absorption is the key for a good sunscreen, other factors are also important. For instance, a water-soluble sunscreen might disappear in minutes if there is profuse sweating. What properties in addition to absorption of UV radiation do you believe are important in making a sunscreen that is commercially viable?
7. Suppose that there was an incredible overnight change in nature and visible radiation became ionizing. Suggest a chemical or class of chemicals that you might use to construct a “sunscreen” in the visible range.
8. UV-B radiation can cause cataracts. Describe a way that uses what you have learned about sunscreens that might be used to prevent cataracts.
9. Benzene and other organic molecules with conjugated double bonds tend to absorb UV radiation strongly, but molecules like water do not. In your own words, describe how a UV or visible spectrum arises and explain briefly why some molecules absorb in the UV and others do not.
10. The textbook for this course by Chang is a blue color due to dyes used to color the fabric of the binding. Using what we have learned about spectroscopy, explain how the dyes give it a blue color. What colors are the dye absorbing?

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Abstract:
The aim of this experiment was to investigate the UV spectrum of three sunscreens with SPF 4, 30 and 50. The spectra were recorded in the region between 240 and 400 nm, and specificity of each of them discussed based on the absorption at 296.7 and 313 nm. The linear relationship was found between SPF and absorbance. Other consequences of UV radiation absorption are also discussed.
Introduction and Theory:
Electromagnetic spectrum consists of the large scale of wavelengths divided into several categories based on the common effects. The rays that are above visible light when energy or frequency is concerned are Ultra-Violet. These rays are not observable by the humane eye, but its effects can be seen especially during longer exposure. When experiments are performed in this region it is important to be sure about the part of UV light that is investigated. The rays with wavelengths that are close to visible part of spectrum are not absorbed by the molecules of gas in air. This part is called air UV-light. Part of rays with higher frequency are absorbed by the molecules of gas and therefore vacuum...

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