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View Full Version : 2LiOH + CO2 => H2O + Li2CO3


Johnny L.A.
05-22-2011, 10:56 AM
I'm watching Moon Machines (yet again), and they mentioned that lithium hydroxide was used to scrub the excess carbon dioxide from the air aboard the spacecraft. In one of those 'I think I'll see how that works' moments, I immediately saw that lithium hydroxide and carbon dioxide make lithium carbonate and water:

2LiOH + CO2 => H2O + Li2CO3

OK, it balances. Each side has two lithiums, four oxygens, two hydrogens, and one carbon. I know that the products are H2O and Li2CO3. But what's actually going on in the reaction?

Here's what I'm thinking: CO2 molecules find LiOH molecules. They say, 'Hey, that looks like a good gig. Let's move in and kick lame-o Hydrogen out!' Lithium has a (+) charge, and carbonate has a (2-) charge, so to make lithium carbonate you need two lithiums (and another oxygen). If you have two lithiums, you also get two oxygens and two hydrogens. So CO2 joins up with Lithium and kicks Mr. Hydrogen and Mr. Hydrogen to the street. Taking a cue from I, Mudd, CO2 looks at Oxygen and Oxygen and says, 'I love you. However, I hate you,' and kicks one of the Oxygen twins out. So now we have two hydrogens and an oxygen standing at the curb saying, 'You bastard!' They all look at each other and say, 'We don't need them! Let's get our own place!' And there's your water.

Do I have that right? I'm not feeling entirely well today, and my mind is moving slowly.

Malacandra
05-22-2011, 12:50 PM
It all looks a bit easier if you factor some water into the equation from the get-go. CO2 + H2O behave much like H2CO3 even if "carbonic acid" is kinda reluctant to exist in any concentration worth mentioning. The acid ionises into H+ and CO32- - that's what acids do - and similarly the alkali ionises into Li+ and OH-. Then you have your typical acid-base reaction in which the alkaline Li+ and CO32- settle down - metal carbonates are much happier than carbonic acid - and the leftover OH- and H+ get jiggy.

Vlad/Igor
05-22-2011, 04:50 PM
-[/sup] and H+ get jiggy.LOL. I gotta remember that the next time I explain acid/base reactions.