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 $C{l}^{-}$ ions from the evolved gas

Answer 1

The correct option is C absorb moisture from the gas

This experiment suggests that hydrogen ions in $HCl$ are produced in the presence of water. The separation of $H^{+}$ ion from $HCl$ molecules cannot occur in the absence of water.

$HCl+H_{2}O\to H_3{O}^{+}+C{l}^{-}$

Hydrogen ions cannot exist alone, but they exist after combining with water molecules. Thus hydrogen ions must always be shown as H+(aq) or hydronium ion ($H_3{O}^{+}$).

$H^{+}+H_{2}O\to H_3{O}^{+}$

We have seen that acids give $H_3{O}^{+}$ or $H^{+}$(aq) ion in water. Bases generate hydroxide $\left(OH\right)$ ions in water. Bases which are soluble in water are called alkalis.

If the climate is very humid, you will have to pass the gas produced through a guard tube (drying tube) containing calcium chloride to dry the gas.