Question

Give the characteristic test for $C{O_2}$ gas.
A. Turns lime water colorless
B. Turns lime water blue
C. Turns lime water milky
D. Turns lime water black

Answer 1

As we can see $C{O_2}$, carbon dioxide contains one carbon atom and two oxygen atoms covalently bonded to each other. It is mostly present in Earth’s atmosphere and also termed as greenhouse gas. Dry ice is the solid form of carbon dioxide. As all the options are regarding lime water, write the reaction of carbon dioxide with lime water and note the changes in the formed products. Lime water is also known as Calcium hydroxide.

Complete answer: We are given to find the characteristic test for $C{O_2}$ gas.
$C{O_2}$ gas is Carbon dioxide. Generally humans inhale oxygen and exhale carbon-dioxide. $C{O_2}$ gas is a colorless gas and the bond between carbon and oxygen atoms in $C{O_2}$ are double bonds.
Lime water is also known as slaked lime which is another name for Calcium hydroxide. The molecular formula of Calcium hydroxide is $Ca{\left( {OH} \right)_2}$ as the oxidation number of Calcium is 2, it has two hydroxyl groups.
When Carbon dioxide is passed through lime water, a white precipitate of calcium carbonate will be formed.
The reaction of the above process is $Ca{\left( {OH} \right)_2} + C{O_2} \to CaC{O_3} + {H_2}O$
Calcium carbonate is insoluble in water. So when carbon dioxide is passed through lime water, it forms a milky white precipitate of calcium carbonate.

Hence, the correct option is Option C, carbon dioxide turns the lime water milky.

Note: Calcium hydroxide is called slaked lime whereas calcium oxide is called quick lime. So be careful with the names of the compounds. Calcium carbonate is also known as Limestone. While writing a chemical reaction, always balance the no. of atoms in the reactants and products.