Question

Carbon dioxide turns lime water __?
(A) green
(B) milky
(C) pinky
(D) none of these

Answer 1

Hint:The chemical formula of Carbon dioxide is \[C{O_2}\]. It is colourless gas with a molecular weight of $44g$. It is treated with lime water which is also called calcium hydroxide with the chemical formula $Ca{(OH)_2}$ to convert the solution into carbonate form.

Complete step by step answer:
Lime water is obtained from lime. Lime whose chemical name is calcium oxide with the chemical formula $CaO$. It has high surface tension and average viscosity. When lime is treated with water it gets converted into an alkaline solution known as slaked lime. Slaked lime or lime water is called calcium hydroxide. It is an exothermic Reaction.
$CaO\,\underrightarrow {{H_2}O}\,Ca{(OH)_2}$
When this calcium hydroxide or lime water is treated with carbon dioxide, it gets converted to calcium carbonate which is a milky solution formed due to the precipitation of insoluble suspension of calcium carbonate:
$Ca{(OH)_2}\, + \,C{O_2} \to CaC{O_3}(s) + {H_2}O$
On passing the carbon dioxide gas through lime water, the solution turns milky. The precipitates that formed are not soluble in water, therefore it settles at the bottom of the solution. But, if you pass excess amounts of carbon dioxide through the solution, it gets converted into calcium bicarbonate and the precipitates get dissolved making a clear solution in the test tube.
$CaC{O_3}\, + \,{H_2}O + C{O_2} \to Ca{(HC{O_3})_2}$
Because of the formation of calcium bicarbonate, the milkiness of the solution disappears.
 So we can say that Carbon dioxide turns lime water milky.
Hence, option (B) is correct.

Note:
Limewater is very soluble in glycerol and acids, but sparingly soluble in ${H_2}O$. $Ca{(OH)_2}$ is used in industrial settings such as the treatment of waste, the manufacturing of paper, building, and used in the processing of foods. It is also used in pesticides, hair care products, and the manufacture of ebonite.