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Old Apr 12th 2017, 06:17 AM   #1
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Carbonate equilibriums

I'm stuck on the last part of an experiment regarding carbonate equilibriums.

First, carbon dioxide gas was bubbled through Ca(OH)2. This produced a cloudy liquid, and then when the gas continued to bubble through, the liquid turned clear again. I'm fine with this part:

Ca(OH)2(aq) + CO2(g) > CaCO3(s) + H2O(l)

CaCO3(s) + CO2(g) + H2O(l) <> Ca2+(aq) + 2H2CO3-(aq)

The solution was then split into three parts, one as a control, and two others. The first of the others was heated, which produced a cloudy solution again. I'm also clear on this - the reaction is exothermic, so adding heat makes it shift left to reduce the amount of heat. Then, to the third test tube, NaHCO3 is added. This is the part I'm stuck on.

From my observation, the test tube went cloudy, but then after a few minutes, the test tube went mostly clear again, which is what I'm stuck on. I understand why it went cloudy at first (adding HCO3- ions means shifting the equilibrium to the left) but what I really don't understand is why it went mostly clear again. I thought it might be because the precipitate was settling but in that case you'd expect the same to happen in the second test tube, which was heated - which didn't happen.

If someone could explain this, that would be great!

Last edited by jessdooper; Apr 12th 2017 at 06:18 AM. Reason: forgot states of matter
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carbonate, equilibrium, limewater

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