Question

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

Answer 1

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`.