2: Carbon atoms and fatty acids
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The molecules of life are built around carbon atoms. Carbon is the “backbone” of proteins, fats, carbohydrates and nucleic acids– the stuff of life.
1) DRAWING LESSON
39 minutes
Sample of final drawing for drawing 2
2) ACTIVITIES
Activity 2-1: Lab: More drops on a penny
You will need a penny, an eye dropper and some vegetable oil, vinegar (which is acetic acid), hydrogen peroxide and rubbing alcohol.
We know that water really stacks up on top of a penny, due to the fact that the molecules are polar and like to stick together. In this lesson we saw a non-polar substance: octane (gasoline). If octane molecules are non-polar and don’t stick together, then it follows, logically, that you should not be able to put very many drops of gasoline on a penny. Watch this video that I made, and see if our prediction comes true. (I don’t recommend doing this at home. Just watch the video.)
Now it’s your turn to try some substances. First, try vegetable oil (any kind), which is made of fatty acids (chain lengths of 12-18 carbon atoms). What do you think will happen? Look at drawing 2 and compare octane to the fatty acid. Does octane have any polarity at all? What about the fatty acid? What about that COOH? Go ahead and try the oil and see what happens.
Next, try vinegar (acetic acid). Take a general guess about its polarity. (Hint- does vinegar dissolve in water?) Then try the experiment.
Lastly, try other substances you have around the house, such as rubbing alcohol or hydrogen peroxide, or others you might think of.
You might want to make a chart showing each substance and how many drops of it will sit on a penny. Then you can go to Wikipedia’s article on surface tension and scroll down to the chart where they have listed many substances and their degree of surface tension. As it turns out, you can divide those numbers by two and get approximately the number of drops that will sit on a penny. Look at mercury. That’s a lot of surface tension! That’s well over a hundred drops on a penny!
If you are unable to actually do the lab but would like to participate via video, click on these links to see my demonstrations:
Vinegar Vegetable Oil Hydrogen peroxide Rubbing alcohol
Activity 2-2: Experimenting with the non-polarity of oils
Activity experimenting with oil droplets in water (download pdf)
3) SUPPLEMENTAL VIDEOS
4) QUIZ
You can re-take the quiz as many times as necessary. You must get 60 percent to pass.
