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Saturday, July 24, 2010

B.S. (Bad Science): Water Marbles

I did a few B.S. sessions last Fall with students who brought in various videos asking if they were real. One was this video of water marbles (Youtube). We walked through this, step by step. Questions to ask:
  1. Combining acetic acid (vinegar: CH3COOH) and sodium bicarbonate (baking soda: NaHCO3) produces sodium acetate, CO2 and water. Hey, maybe these guys are on to something! If one wants to supply B.S. (Bad Science), it is critical first to supply truth. Famous liars: Satan, Iago, Jabba the Hut.
  2. The next step is calcium carbonate (shown in video as a solid but according to Wiki exists only in the aqueous form (ions dissolved). It sure looks and sounds scientific though.
  3. Also, grab some "ionized salt." Look up ion. Look up salt. One exists as a solid, the other is what happens when dissolved. Well, it could a typo for iodized salt.
  4. What happens when you add Calcium bicarbonate to Sodium acetate? What kind of reaction is that? Double Displacment: Ca(HCO3)2 + 2NaCH3COO --> 2NaHCO3 + Ca(C2H3O2)2. According to our equation, we just made more baking soda and calcium acetate (check out uses). Both of these are bases.
  5. Wiki: "Chemistry teachers often prepare 'California Snowballs,' a mixture of calcium acetate solution and ethanol." Sounds fun. Probably the baking soda would interfere, unfortunately.
  6. The fizz shown in the video (what caused the fizz earlier? What causes fizz in soda pop?) must be residual vinegar mixing with baking soda.
  7. Where'd all that liquid come from? (Conservation of Matter)
  8. Take a look at the size and shape of all those marbles. What do you notice? Why is that unusual?
  9. How did the water turn purple? Why might it be important to use coloring? Refractive index of the marbles hidden in the water must be quite similar. Also, it doesn't hurt to be looking at the water through a translucent plastic.
  10. Have the student most convinced of the reality of these water marbles look up "polar hability." Would water be water if it stopped being polar? What makes water polar? What would happen if water were no longer polar? Would it stick to itself? I have no idea what hability is.
  11. How can water be a solid if what you were making was a polymer of calcium acetate?
  12. What happens to the water marble that falls outside the plastic tub?
Somehow I still had a student who wanted replicate this experiment.

If I've gotten anything wrong, feel free to share.

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