f3chemistry problem

Your teacher is rite . If more CO2 is is added to the milky solution , it will turn clear . As more CO2 in water , carbonic acid is formed , it is a weakly acid which will react with calcium carbonate & will form a soluble calcium bicarbonate solution . This is why the milky solution turns clear again .
CO2 + H2O -----. H2CO3
CaCO3 + H2CO3 -----> Ca(HCO3)2 The calcium bicarbonate exists only in aqueous solution that you cannot isolate it in crystal form as KHCO3 .

2010-12-11 11:41:21 補充：
Boy , this test have done 48 years ago !!!!

Ca(OH)2 + CO 2 = CaCO3 + H2O


calcium hydroxide solution(limewater) turns milky when react with carbon dioxide, it turns milky because the calcium carbonate (CaCO3) is formed, this substance can not solve in water, it is still a solid, it gives the milky colour.


CaCO3 + H2O + CO2 = Ca(HCO3)2


if more carbon dioxide is added, the calcium carbonate react with carbon dioxide and form calcium hydrogencarbonate ( Ca(HCO3)2 ) , it is soluble in water, so it dissolves in the water and the solution become colourless again.

Isps5a_18, your should work harder on f.4 chemistry. calcium carbonate will react with extra, excess carbon dioxide.
also notice the keyword "more".

Solution turns milky due to CaCO3 which is water insoluble.

Ca(OH)2 + CO2 → CaCO3 + H2O


Excess CO2 react with CaCO3 and becomes Ca(HCO3)2 and it is water soluble,thus it becomes colourless again.

CaCO3 + CO2 + H2O → Ca(HCO3)2

2010-12-08 21:41:14 補充：
Excess CO2 WILL react

Maybe your teacher is wrong , Calcium hydroxide solution react with water will form calcium carbonate and water . Calcium carbonate is a white solid which is insoluble in water and appear as white precipitate so it turn the colourless lime water milky .

2010-12-12 18:57:54 補充：
Sorry about that , and thank you too . I learnt extra knowledge indeed