Monday, June 11, 2012

Element of the Month: Calcium!

June's Element of the Month:


Atomic Mass: 40.078  amu
Melting Point: 842 °C
Boiling Point: 1484 °C

You'd think Calcium would be all white and powdery, like an antiacid or bonemeal or chalk or lime, but those are all various compounds of Calcium. You need "Big Ca" (as its pals call it) for your bones, sure, but you need it in tandem with phosphate (which itself is a compound of Phosphorus, Oxygen, and Hydrogen). Lime is Calcium hydroxide, Tums are a form of Calcium carbonate with sugar and flavoring thrown in, and chalk, at least the kind you use on a chalkboard, is Calcium sulfate. No, Calcium itself is neither white nor powdery.  It is, rather -- wait for it -- a silvery-grey metal! Just like almost everything else. It's pretty much a big metal world, except for the enormously more abundant colorless, odorless gasses.

You'd probably also think that Calcium would be a relatively common element here on the surface of Planet Earth, not one of those obscure oddballs that occurs only in certain Chilean clays and that sharp Swedish scientists only managed to isolate during the 1930s. This time around, you'd be quite correct. Calcium is the fifth most abundent element in the Earth's crust (well behind Oxygen, Silicon, and Aluminum, but challenging Iron), and the fifth most abundent element in your body (trailing Oxygen, Carbon, Hydrogen, and Nitrogen). So there's plenty of it around, locally. But since it's highly reactive with other common elements, its elemental form doesn't occur in nature. That's why it took the incredibly brainy Sir Humphrey Davy to derive a sample of the pure stuff, back in 1808.

The Centerfold!

There are a zillion industrial Calcium compounds, but the raw stuff isn't used for much outside of alloys plus the manufacture of cement and, um, cheese. And frankly, I'm not sure I'm buying that anybody puts actual elemental Calcium metal into either cement or cheese. (Elizabeth?)  In fact, I don't get the impression that there's much elemental Calcium produced at all.  If you want to use some Calcium carbonate, say, I bet you refine Calcium carbonate directly from minerals (like gypsum, say) rather than going all the way down to elemental Calcium and Carbon and Oxygen and building it back up. That's the way ~I'd~ try it if I had to come up with a system from scratch, anyway.

Here's an interesting thing: when Calcium is weathered out of exposed minerals and carried down to the ocean, it reacts with seawater to form limestone in a way that removes one molecule of Carbon Dioxide from the sea per atom of Calcium. So if it started to look like Earth was in danger of annihilation by Venus-style runaway CO2 atmosphere change, a last-ditch attempt to forestall the end might be to grind up all the limestone we could find into the finest powder possible and to dump it by the superfreighter into the world's oceans.

Warning: Talk to your marine scientist and one or more real geochemists before deciding if superfreighters of powdered limestone are right for you. Side effects may include a wide variety of multiple unintended consequences, potentially including alternative routes to accidental terracide.


Elizabeth said...

I always wondered what that jar of silvery-grey metal was on the shelf, the one that Pat never talked about ...

No, in fact (and I quote) "Calcium choride is added to replace calcium redistributed during pasteurization. Milk coagulation by rennet during cheese making requires an optimum balance among ionic calcium and both soluble insoluble calcium phosphate salts. Because calcium phosphates have reverse solubility with respect to temperature, the heat treatment from pasteurization causes the equilibrium to shift towards insoluble forms and depletes both soluble calcium phosphates and ionic calcium. Near normal equilibrium is restored during 24 - 48 hours of cold storage, but cheese makers can't wait that long, so CaCl2 is added to restore ionic calcium and improve rennetability. The calcium assists in coagulation and reduces the amount of rennet required."

Michael5000 said...

THANK you! I thought it would be something like that.