Question

An unknown gas is likely to be carbon dioxide if it has which of the following

characteristics?
A
turns limewater milky
B. is flammable
c. is less dense than air
D. has a penetrating odor

Answer 1

An unknown gas is likely to be carbon dioxide if it turns limewater milky.

Option a

Step-by-step explanation:

Calcium Hydroxide also known as lime
`Ca(OH)_2` is a sparingly soluble compound which when dissolved in water produces an alkaline solution known as lime water. When a gas such as carbon dioxide
`( CO_2 )` passes through this alkaline solution, it turns lime water milky due to the formation of an insoluble suspension of calcium carbonate
`( CaCO_3 )`. This can be understood by the following chemical reaction-

`Ca(OH)_2 (aq) + CO_2 (g) \rightarrow CaCO_3 (s) + H_2O (l)`

If an excess amount of
`CO_2` gas is added in the solution, the following reaction takes place:

`CaCO_3 (s) + H_2O (l) + CO_2 (g) \rightarrow Ca(HCO_3)_2 (aq)`

At this stage, the milkiness of the solution disappears since "calcium bicarbonate is soluble in water".