Question

Calcium hydroxide reacts with carbon dioxide to form _____?
A.Calcium carbonate and water
B.Calcium carbonate and hydrogen
C.Calcium bicarbonate and water
D.None of the above

Answer 1

Hint: We can define a double displacement reaction as the type of reactions that occurs when the cation and the anions switch between two reactants to form new products. In order for the reaction to occur, one of the products is usually a solid precipitate, a gas or a molecular compound.
An acid-base reaction is a type of double displacement reaction where the chemical reaction between an acid and a base is called a neutralization reaction. The ionic compound formed along with water in this reaction is called salt.

Complete step by step answer:In aqueous solution, calcium hydroxide reacts with carbon dioxide to form calcium carbonate and water.
We can give mechanism of this reaction as follows,
Carbon dioxide gets dissolved in water to form carbonic acid. We can write the chemical reaction as,
$C{O_2}\left( g \right) + {H_2}O\left( l \right)\xrightarrow{{}}{H_2}C{O_3}\left( {aq} \right)$
The carbonic acid then reacts with calcium hydroxide to give calcium carbonate and water. We can write the chemical reaction as,
$Ca{\left( {OH} \right)_2}\left( {aq} \right) + {H_2}C{O_3}\left( {aq} \right)\xrightarrow{{}}CaC{O_3}\left( s \right) + {H_2}O\left( l \right)$
The calcium carbonate formed is a precipitate and it is not soluble in water. Calcium carbonate appears as a white solid. We can see that the solution appears to be milky due to the formation of calcium carbonate.
We can call the reaction of calcium carbonate with carbon dioxide as a precipitation reaction because in this reaction a white solid precipitate named calcium carbonate is obtained.
Calcium hydroxide is otherwise called limewater.

$\therefore $Option A is correct.


Note:
When we add excess amounts of carbon dioxide, the precipitate dissolves to give a colourless solution of calcium hydrogen carbonate/calcium bicarbonate. We can write the reaction of formation of calcium hydrogen carbonate as,
$CaC{O_3}\left( s \right) + C{O_2}\left( g \right) + {H_2}O\left( l \right)\xrightarrow{{}}Ca{\left( {HC{O_3}} \right)_2}\left( {aq} \right)$
We can use this reaction as a test for identifying carbon dioxide. When we add carbon dioxide through limewater the solution changes from colourless to milky.