When carbon dioxide is passed through lime water, it turns milky. Why?

1 Answer
Jun 17, 2017

Answer:

Because carbon dioxide forms an insoluble carbonate with lime water........

Explanation:

#"Limewater"# is SATURATED #Ca(OH)_2(aq)# (and in fact calcium hydroxide is reasonably insoluble in aqueous solution). It undergoes the following reaction with carbon dioxide.....

#Ca(OH)_2(aq) + CO_2(aq) rarr CaCO_3(s)darr + H_2O(l)#

Calcium carbonate precipitates as a milky white precipitate. And in fact this is a qualitative test for the presence of hydroxide salts.

When you do these reactions, you should pre-do a test with limewater, and a source of #CO_2(aq)#, so that you know the results of a positive test. And in fact the best source of #CO_2(aq)# is sparkling mineral water, which is certainly saturated (probably supersaturated) with respect to #CO_2#.