Our Chemical World #3:
Sunscreens This assignment was due before noon on Friday, March 28.
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Welcome back to Our Chemical World. This is another opportunity to get extra credit while solidifying your understanding of Chapters 4, 5 and 6.
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The web site, What’s That Stuff, discusses and explains the chemistry of some everyday materials whose “active ingredients” are simple ionic and covalent compounds.
This assignment is focused on the ionic and covalent compounds used in sunscreens.
Click on the link to learn about sunscreens, then come back and answer the following questions. Remember, the answers are not necessarily all found in the article, but you should be able to combine the information in the article with the chemical knowledge you now have, your lecture notes, and your textbook to answer the questions.
Sunscreens
Chemists use sets of rules to name chemical compounds. However, substances that have been known for a long time are often known by a common name. For example, the systematic name for water (H2O) is dihydrogen oxide. Titanium dioxide, a white pigment that is used in paints and sunscreens, is the common name for TiO2. Although the common name implies that TiO2 is a covalent compound, its melting point is 1855oC. Based on what you know about properties of ionic and covalent compounds, which system (ionic or covalent) should be used to name TiO2? (Hint: Do you need a Roman numeral?) What would the correct systematic name be?
PABA, an acronym for p-aminobenzoic acid, is a compound that was used for years as a sunscreen. Its structure is shown here. It is a covalently-bonded compound. If you shop the aisles at your local drugstore, you are not likely to find sunscreens containing PABA, although you will find many that highlight the fact that they are PABA-free.
PABA p-aminobenozoic acid
PABA has been replaced by other compounds such as octyl methoxycinnamate (aka OMC or Parsol) shown here. Use the Lewis structure of OMC to answer the following questions about this molecule.
What are the bond angles at arrows I, II and IV?
What's That Stuff, a web site maintained by the American Chemical Society, has links to other fun stuff like Cheez Whiz, new car smell, and teeth whiteners. Bookmark it and check it out sometime for fun. (Yes, we know, we are geeks.)
What's That Stuff
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