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Sci Advisor
P: 1,395
 Quote by Kyoma Okay, I think I kinda get it. I will try. CO32- + H2O -------> HCO3- + OH- I think this is the equation. So, if you add calcium carbonate to water, the calcium ions would be bonded to the hydroxide ions above to form calcium hydroxide. Am I right?
Yup! That is the correct interpretation [EDIT: I should point out that it is correct only for the carbonate ions that are dissolved in solution. You also need to take the stoichiometry of the problem into account, since carbonate and hydroxide ions have different charges]. Do you now understand why the relative solubilities of sodium hydroxide and calcium hydroxide are important for this case?

[EDIT: whoops! I really meant sodium carbonate and calcium carbonate in the last sentence above. The solubilities of sodium hydroxide and calcium hydroxide are also relevant to the problem, but aren't as important.]