Question

When carbon dioxide is passed through lime water, it turns milky due to the formation of:
A) Calcium hydroxide
B) Calcium carbonate
C) Calcium oxide
D) Calcium

Answer 1

It is a common substance that is found in rocks as the minerals of aragonite and calcite. It is the main component of pearls and the shells of marine organisms, snails, and eggs. It appears as white, odorless powder or colorless crystals.

Complete answer:
Pure lime, or quicklime, is calcium oxide. It is an important industrial chemical because of the chemical properties and ease of manufacturing. Limewater can be prepared by mixing the calcium hydroxide with water and removing the excess undissolved solute.
Lime water is calcium hydroxide and when carbon dioxide gas is passed through the limewater for a short time, it turns milky due to the formation of calcium carbonate.
The reaction is-
$Ca{\left( {OH} \right)_2} + C{O_2} \to CaC{O_3} + {H_2}O$

Thus the correct answer is B. i.e., Calcium Carbonate.

Additional Information: However, when excess of $CO_2$ is passed through this solution, the milkiness disappears. This is due to the formation of calcium bicarbonate which is colorless and soluble in water.
The reaction is-
$CaC{O_3} + C{O_2} + {H_2}O \to Ca{\left( {HC{O_3}} \right)_2}$
The above chemical properties are commonly used for testing the presence of carbon dioxide in gaseous samples in school laboratories, and refining of sugar in a process called carbonation.

Note: Calcium carbonate is a chemical compound and it shares the same typical properties of the other carbonates. The vast majority of the calcium carbonate is used in industry that is extracted by mining or quarrying. It is also used in the purification of the iron from an iron ore in a blast furnace.