Question

When air is blown from mouth into a test tube containing lime water the lime water turned milky why

Answer 1

The lime water turns from colourless to milky.

This is because the exhaled air contains about 4% CO2.

CO2 reacts with lime water to form a milky coloured compound.

Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)

If excess CO2 is added, the following reaction takes place:

CaCO3(s) + H2O(l) + CO2(g) → Ca(HCO3)2(aq)

The milkiness disappears since calcium bicarbonate is water-soluble.

Answer 2

the lime water turns milky showing the presence of CO2.
the air blown inside must be containing CO2