Question

Quicklime is not used to dry HCl gas because _________ (CaO is alkaline, CaO is acidic, CaO is neutral)

Answer 1

CaO is the chemical formula for Calcium Oxide. This is also known as quicklime or burnt lime. It is an amorphous white solid at the room temperature. It has a high melting and boiling point. CaO will form slaked lime in presence of water.

Complete Solution :
When a base and an acid react together, it produces water and salt. This process is called a neutralization reaction.
A strong acid is the one that fully dissociates in the water to give ${H^ + }$ ions. A weak acid that cannot fully dissociate, rather partially dissociates in water to give ${H^ + }$ ions.
A strong base is the one that can fully dissociate to release $O{H^ - }$ ions. A weak base that cannot fully dissociate, rather partially dissociates in water to give $O{H^ - }$ ions.
If quicklime is used to dry HCl gas, it will start to react with HCl. Since HCl behaves as an acid and CaO behaves like a base, a neutralization reaction takes place in between them. They form water and calcium chloride salt. Hence, CaO can never be used to dry HCl gas.
Rather, concentrated sulphuric acid is used to dry or purify HCl gas.
$CaO + 2HCl \to CaC{l_2} + {H_2}O$

The answer is CaO is alkaline.
It is clearly evident that CaO is alkaline because it reacts with HCl, which is an acid, to produce salt and water.

Additional Information:
CaO is used for various purposes such as
- For medicinal uses.
- It is used for softening water.
- In recovery of ammonia.
- Improving soil quality
- Preservative for poultry feed.
- It was also used as a binding agent in buildings, but now it has been replaced by cement.

Note: In order to determine the substance or solution is acidic, basic or neutral, we can use the $pH$ scale.
- When the $pH$ value is below 7, the solution is acidic.
- When the $pH$ value is above 7, the solution is basic.
- When the $pH$ value is equal to 7, the solution is neutral.