Sink or swim? from chemistry notes

It's been hot in the coastal foothills of California (afternoon highs ranging from 102 to 107F), and we've been cooling off in the pool and with a steady supply of cold drinks. But the search for truth marches on, even on vacation, and in that spirit we did a little experimentation this afternoon. Does Diet Coke ™ really float, while the high calorie stuff sinks? Not having any on hand, we substituted Diet 7-Up and Sierra Mist (non-diet) and dropped away. Sure enough the diet stuff floats.

Why? The cans are the same size, but the non-diet soda weighs more. Why? Do calories have mass? One of my brothers suggested it was because sugar is a heavier molecule than aspartame (NutraSweet ™). This is true - sucrose weighs in at 342.3 daltons while aspartame comes in just under 300 (294.3 daltons), but not the solution to the mystery. The relative sweetness of the two molecules is the key. You need less than 100 mg of aspartame to equal the sweetness of the roughly 40 g of sugar in the regular soda. Both have the same volume of solution, the sugar one is denser than water and sinks. But wait...why isn't the diet stuff denser than water, too? It should be just a little heavier than just plain water not? True, but the air bubble in the top of the can is just enough to offset it.

A holiday at the intersection of biology and chemisty

I'm on vacation in California taking care of my dad's 10 acre farm while he is out of town. The resident fauna include 2 watch llamas and a small flock of Barbados sheep (self-shearing). When I arrived the flock had 11 sheep - now there are 16. If you're counting (and I am, every morning), that means that 5 new sheep have appeared. Four of them were born in the space of 2 hours a week ago last Saturday in the 107 degree heat of the afternoon. Birth is a messy business, and in the end I sacrified not one, but 2 white t-shirts to the process.

After the biology had settled down and was nursing happily, I turned to chemistry to get the stains out of my shirt. My dad (experienced in these matters) advised no bleach, and soaking in a strong salt solution. Why no bleach? Bleach is an oxidant, and "removes" (or at least decolorizes) many stains by oxidizing the carbon-carbon double-bonds which are responsible for the color. The red color of blood comes from the oxyhemoglobin. Oxidizing the iron in the hemoglobin produces iron oxide - aka rust - not necessarily an improvement on the front of your t-shirt.

---

One of the new arrivals.