Question

A substance absorbs $C{{O}_{2}}$ and violently reacts with water. That substance is:
A. $CaC{{O}_{3}}$
B. $CaO$
C. ${{H}_{2}}S{{O}_{4}}$
D. $ZnO$

Answer 1

Hint: As we know that drying agents are the hygroscopic substance that basically induces a state of dryness in its place. There are strong bases like sodium hydroxide, soda-lime, lithium hydroxide and potassium hydroxide that can remove carbon dioxide gas by reacting with it.

Complete Solution :
- $CaC{{O}_{3}}$ and $ZnO$ doesn’t absorb $C{{O}_{2}}$ and doesn’t violently react with water. It is also found that these are not dehydrating agents, hence we can eliminate these options.
- ${{H}_{2}}S{{O}_{4}}$ has a strong affinity for water and is found to be a very good dehydrating agent, but doesn’t absorbs $C{{O}_{2}}$. Hence, we will eliminate this option.
- Out of the given options only calcium oxide Cao react with carbon dioxide to form calcium carbonate. We can see the reaction that takes place:
\[CaO+C{{O}_{2}}\to CaC{{O}_{3}}\]

- We can see that calcium oxide acts as a drying agent. We can write the reaction when CaO reacts with water as:
\[CaO+{{H}_{2}}O\to Ca{{\left( OH \right)}_{2}}\]
- Hence, we can conclude that the correct option is (b), that is CaO absorbs $C{{O}_{2}}$ and violently reacts with water.
So, the correct answer is “Option B”.

Note: - We must know that there are various drying agents like magnesium sulphate, calcium chloride etc. When these were added to a solution, these pick up an extra water molecule from the solution. And hence, become hydrated. Further these clumps, and can be filtered or left behind during the process of decanting.