Question

During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through the guard tube containing anhydrous calcium chloride. The role of anhydrous calcium chloride taken in the guard tube is to:
A.Absorb the evolved gas
B.moisten the gas
C.absorb moisture from the gas
D.absorb $Cl^–$ ions from the evolved gas

Answer 1

Hint: Anhydrous Calcium (\[CaC{l_2}\]) is an inorganic compound which is hygroscopic (tendency of holding water molecules) so it is used as desiccant (state of dryness)

Complete answer:
If we see how hydrogen chloride gas is prepared, we will see that the gas is usually passed through a guard tube (also known as a drying tube) containing anhydrous calcium chloride. The reason behind why anhydrous calcium chloride is used in guard tubes is because it is considered as a very good drying agent.
If we see what a drying agent is: we will get to know that drying agents acquire water of hydration when they are exposed to wet solutions or moist air.
If we see overall properties of anhydrous calcium chloride we will conclude that it is the best example or best used as a dehydrating or drying agent which absorbs the moisture of water content from the gas hence making it dry.
Overall if we see and consider all the above facts we will see that the main role of anhydrous calcium chloride is to absorb moisture from the gas.
And hence our correct option is C.

Additional Information:
Anhydrous calcium chloride can also refer to calcium (II) chloride or calcium dichloride. It has various uses such as de-icing, freezing, road surfacing and food. It is an ionic compound which consists of calcium cation (\[C{a^{2 + }}\]) and two chlorine anions (\[C{l^- }\]
It is mainly produced by reacting limestone (\[CaC{O_3}\]) with hydrochloric acid (\[HCl\]):
\[CaC{O_3} + 2{{ }}HCl \to CaC{l_2} + C{O_2} + {H_2}O\]

It is also produced as a major by-product during manufacture of soda ash in which limestone is reacted with \[NaCl\] solution.
It is an odorless white powder or granules. It has a density of 2.15 g/mL and melting point and boiling point at 782 °C and over 1600 °C respectively.

Note:The main property that we should remember is that anhydrous calcium chloride is considered as a very good drying agent as it absorbs moisture. Anhydrous calcium chloride has a very good tendency of holding the water molecules and hence it is used as a desiccant in most of the experiments in the guard tube.