Saturday, 25 February 2012

By on February 25th, 2012 in science kits

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.

9 Comments and discussion on "Saturday, 25 February 2012"

  1. SteveF says:

    Can’t sodium bicarbonate absorb water? Wouldn’t that throw off the mass calculation?

  2. Robert Bruce Thompson says:

    Sodium carbonate exists in numerous hydrated forms, from the monohydrate to the decahydrate, and any random sample is likely to have an arbitrary amount of water. Sodium bicarbonate exists, as far as I know, only in the anhydrous form.

  3. SteveF says:

    Hmm. Well, I value your statements on these matters higher than I value the stuff I find on arbitrary internet sites. Yesterday I checked before putting up my comment and found that, yes, it’s “common wisdom” that you can absorb moisture as well as odor with baking soda. A second site agreed and added a “and here’s why” section. But I didn’t check on the authors at all. For all I know, a full and accurate biography would say “Bill is a high school freshman who spends four hours a day talking out his ass on scientific and legal advice sites.”

  4. OFD says:

    That topic just came up briefly with one of my British friends on FB; i.e., the number of cretins, morons and mental defectives who opine on all sundry matters at length on the net while knowing naught about any of them. Which can be downright dangerous at times, esp. with matters chemical and medicinal, one reckons.

    OFD is a college grad in English literature who spends a couple of hours a day talking out his ass on political and religious matters at various sites.

  5. Miles_Teg says:

    Mum filled my mind with a lot of pop wisdom, including this:

    It is better to remain silent and be thought a fool than to speak and remove all doubt.

  6. Robert Bruce Thompson says:

    Oh, baking soda can adsorb water (and odors), in the same sense that activated carbon, clay, or silica gel (or, for that matter, sand) can. But that differs from hydration, where the water permeates the material and actually becomes a part of the structure.

  7. BGrigg says:

    You can find anything you want on the internet, and some of it is true. The trick is divining which is which.

    Bill (long past being a freshman, BTW)
    Who talks out of his ass to practice his ventriloquism.

  8. BGrigg says:

    And it’s more like six hours a day…

  9. Chuck Waggoner says:

    This is actually a good subject, because I have no interest in verifying everything I read or am told, even though my education-oriented son thinks I should thoroughly research everything I learn or hear. Thus — as I am sure most of us do — I implicitly trust family members or people that we think should know about a particular subject. Sometimes it is a rude awakening to have that confidence in someone else shattered when finding something they told you about a subject they should know, turns out to be utterly false.

    Years ago, I heard a talk show interviewing a couple of executives about an electronics product company they said was started in Canada. The two guys stated that — in spite of the Candian origin — they used an oriental-sounding name, because people had gotten used to such things with names like Panasonic, Sony, Samsung, and others. I told someone in the family, about this, and they later used that information as fact in a meeting, only to find out that the company was not Canadian at all, but started in an Asian country. Now you would think when two top executives of a company are interviewed, they would tell the truth, but apparently not. Either that, or the whole interview was a joke or a fraud. Unfortunately, that family member would never again talk business with me. And I don’t blame him.

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