# Reactions between Ca(OH)2 and CO2, and Sr(OH)2 and CO2

So I'm doing an investigation, and it involves using supersaturated solutions of Ca(OH)2 and of Sr(OH)2. I notice that there's always a flaky precipitate formed on top. I need to know about the reactions with carbon dioxide. Is it carbonate that's formed? Or is it hydrogen carbonate? Why?

• In my opinion nothing prevents both carbonates and bicarbonates from forming those flakes on the surface; out of curiosity, why is it so crucial to determine which one is it? – andselisk Mar 17 at 12:33
• Although knowing the identity of the precipitate is not really significant to my results in any ways, it's very important that I discuss it since the investigation is for my IB Chemistry Extended Essay. I am required to discuss basically everything going on in the solution in as much detail as possible. I just thought I'd probably be marked down if it I had no idea what's going on in my solutions.. – Mohamad Mar 17 at 12:36
• Interesting, I didn't think of the possibility that it's both. Could be. Thanks! – Mohamad Mar 17 at 12:37
• it is calcium carbonate that is forming. – Nilay Ghosh Mar 17 at 17:15

$$\ce{Ca(OH)2 (aq)+ 2CO2 (aq/g) <=> Ca^2+ + 2(HCO3)- (aq) <=> CaCO3 (s) + CO2 (aq/g)}$$