Question

Identify X in the following reaction:

${\text{Ca(OH)}}_2\text{(aq)}+2\text{X}$ $\to$ ${\text{CaCl}}_2\text{(aq)}+2{\text{H}}_2\text{O}\text{(l)}$

• A. ${\text{H}}_2{\text{SO}}_4$
• B. ${\text{HNO}}_3$
• C. $\text{HCl}$
• D. ${\text{H}}_2{\text{CO}}_3$

Answer 1

The correct option is C $\text{HCl}$

Calcium hydroxide is a base which on reaction with 'X' produces calcium chloride salt and water.

Since salt and water are the only products formed when the base reacts with 'X', it will be acidic in nature. This type of reaction in which an acid reacts with base to give salt and water is called a neutralisation reaction.

In a neutralisation reaction, the salt formed gets its anion (${\text{Cl}}^{-}$) from the acid and cation (${\text{Ca}}^{2+}$) from the base. Thus, the acid (X) is hydrochloric acid ($\text{HCl}$).

So the complete reaction is:
${\text{Ca(OH)}}_2\text{(aq)}+2\text{HCl (aq)}\to {\text{CaCl}}_2\text{(aq)}+2{\text{H}}_2\text{O (l)}$