Question

What happens when?
${\text{A)}}$ bleaching powder is kept open in air.
${\text{B)}}$ chlorine gas is passed through dry slaked lime.

Answer 1

Hint- Here, we will be discussing bleaching powder, chlorine gas and dry slaked lime. Then, we will be writing down the balanced chemical reaction when bleaching powder reacts with carbon dioxide present in the atmosphere and also the reaction involved in the preparation of bleaching powder.

Complete answer:
Bleaching powder's chemical formula is ${\text{CaOC}}{{\text{l}}_2}$ and has a chemical name as Calcium hypochlorite This is a light yellowish powder, with a heavy chlorine scent. It is soluble in water but we never find a clear solution due to the presence of impurities.
${\text{A)}}$. If bleaching powder is held exposed in the air, it reacts with carbon dioxide (${\text{C}}{{\text{O}}_2}$) from the atmosphere to produce calcium carbonate (${\text{CaC}}{{\text{O}}_3}$) and chlorine gas (${\text{C}}{{\text{l}}_2}$).
${\text{CaOC}}{{\text{l}}_2} + {\text{C}}{{\text{O}}_2} \to {\text{CaC}}{{\text{O}}_3} + {\text{C}}{{\text{l}}_2}$
Calcium carbonate is a food supplement that is used when the calcium contained in the diet is not adequate. For healthy bones, muscles, nervous system and heart the body requires calcium. Also, calcium carbonate is used as an antacid to relieve heartburn, acid indigestion and stomach discomfort. Of all the bridging materials, calcium carbonate is the most common. It is typically made of dolomite or marble, and is also available in a wide variety of sizes.
Chlorine is a compound used in manufacturing and in goods for the household washing. Chlorine is a gas, at room temperature. It has a yellow-green colour, and an unpleasant, pungent smell similar to bleach.
Chlorine is used in chloride preparation, chlorinated solvents, pesticides, polymers, synthetic rubbers, and coolants.

${\text{B)}}$. Calcium hydroxide has a chemical name of dry slaked lime and its chemical formula is \[{\text{Ca}}{\left( {{\text{OH}}} \right)_2}\]. It is a colorless crystal or white powder and is formed when water is mixed or slacked with quicklime or calcium oxide (\[{\text{CaO}}\]). This has many names like hydrated lime, caustic lime, builder's lime, slack lime, or pickling lime.
When the chlorine gas (\[{\text{C}}{{\text{l}}_2}\]) is passed through the dry slaked lime (\[{\text{Ca}}{\left( {{\text{OH}}} \right)_2}\]), bleaching powder (\[{\text{CaOC}}{{\text{l}}_2}\]) is formed along with water molecules (\[{{\text{H}}_2}{\text{O}}\]).
 \[{\text{Ca}}{\left( {{\text{OH}}} \right)_2} + {\text{C}}{{\text{l}}_2} \to {\text{CaOC}}{{\text{l}}_2} + {{\text{H}}_2}{\text{O}}\]

Note- There are many uses of chlorine. It is used to clean water and is a part of the wastewater and industrial waste sanitation cycle. The chlorine is used as a bleaching agent during the processing of paper and fabric. This is also used for cleaning items, including household bleach which is water-dissolved chlorine.