09:47 – I spent some time in the lab yesterday making up solutions for the biology kit. This afternoon, Barbara and I will fill, seal, and label 60 sets of those bottles. She’s taking Monday off, so we’ll continue doing bottles tomorrow and Monday as well. After that, we probably need one more weekend to finish making up all the chemical bottles. Once all those are done, we’ll be ready to start building biology kits.
11:18 – Hmmm. While I was downstairs doing laundry, I decided to make up some of the solutions that I hadn’t made yet. I was in the process of making up two liters of Benedict’s qualitative reagent, which requires (among other things) 200 grams of anhydrous sodium carbonate. I had a 500 gram bottle of reagent-grade anhydrous sodium carbonate, but when I opened it I didn’t like the looks of it. It was supposed to be a powder, but it had formed rock-like chunks. Who knows how much water it had absorbed through an apparently-faulty seal?
I decided I’d dry it out later, but in the meantime I needed 200 grams of the stuff. So I carried my 12-pound (5.5 kilo) zip-lock plastic bag full of baking soda upstairs, weighed out 654.81 grams of it into a glass baking dish, and put it in a 450 ºF (232 ºC) oven, and set the timer for an hour. At temperatures above 200 ºC, two molecules of sodium bicarbonate form one molecule each of sodium carbonate, carbon dioxide, and water. The latter two are gases, which leaves only solid anhydrous sodium carbonate powder in the baking dish.
So why 654.81 grams? The balanced equation for the reaction told me that I’d need about 317.1 grams of sodium bicarbonate to yield 200.0 grams of sodium carbonate. I decided that as long as I was at it, I’d make up about twice as much as I needed at the moment. That 654.81 grams of sodium bicarbonate should yield 413.02 grams of anhydrous sodium carbonate. By weighing the product, I can make sure the conversion was quantitative and that what’s left in the baking dish is actually pure sodium carbonate.