Anti-Archimedes

The recipe for pulled pork called for 1/2 cup of brown sugar to be dissolved into 1 1/2 cups of apple cider vinegar. What I had in the cabinet was solid as a rock - there was no way I was packing this into a measuring cup. (Yes, I know I could have done this in the microwave...) My scale came to the rescue. I hacked off chunks until I had the correct mass of brown sugar (110 grams more or less). I dumped the three large hunks into the vinegar in a 2 cup glass measure, and noted that the total volume was just about 2 cups. Nice job.

Then I stirred it to dissolve the sugar. And watched the volume decrease to just over 1 1/2 cups of solution! Have I just proved Archimedes wrong? The volume of sugar at first seemed to have displaced the equivalent volume of liquid, but then seemed to vanish...well not exactly into thin air, but vanish nonetheless. As my 15-year old might say, "What's up with that?"

Yes, Archimedes was correct, but his theory did not address substances that dissolve in the liquid. This is a good demonstration of how much "empty "space is in a liquid. The sugar molecules (and other things in brown sugar, which is not terribly pure as chemicals go) insert themselves between water molecules, without needing to push the water molecules further apart. To a good first approximation the volume of a solution made from a solvent and soluble solid is the volume of the solvent used, not the sum of the two volumes.

Try it...it's fun to watch, and it still intrigues me to think about the amount of unused space there is in a liquid that seems so substantial at the macroscopic level!

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The pulled pork was a keeper...though the kids found the BBQ sauce too spicy for their taste. Try it on challah rolls!

Weird Words of Science 8: Ligands, the ties that bind

Many transition metals react with bases (such as ammonia) to produce beautifully colored transition metal-ligand complexes. The word ligand comes from the Latin ligare which means to tie or bind. The same root leads to ligaments, which tie your bones together.

The photo shows green Ni(H₂O)₆²⁺ and blue green Ni(NH₃)₆²⁺. The ligands are water and ammonia respectively, "tied" to the Ni(II) center. The ligands form an octahedron around the metal center.