Question

What is the other reactant in the following reaction?
$?+C{{O}_{2}}\to CaC{{O}_{3}}+{{H}_{2}}O$
A. $CaOH$
B. $Ca{{(OH)}_{3}}$
C. $Ca{{(OH)}_{2}}$
D. None of these

Answer 1

Hint: We know that $Ca$ is alkaline earth metal from the 2nd group in periodic table and it can lose 2 electrons, it means its oxidation state is +2.

Complete step-by-step answer:
So, as we know that the oxidation state of calcium is +2, it gives 2 electrons to make ionic bonds with hydroxide. And the oxidation state of an hydroxide ion is +1. So, it can make only one ionic bond. So, calcium required two hydroxide ions. So, if we see the options then “C” is the correct option according to the valency of calcium.
And if we see the reaction then: calcium hydroxide or lime water (also known as slaked lime) when reacts with “carbon dioxide gas” to form an insoluble milky calcium carbonate of white precipitate and water. The mechanism of reaction of carbon dioxide in aqueous calcium hydroxide is a double displacement reaction. So, the reaction is:
$Ca{{(OH)}_{2}}+C{{O}_{2}}\to CaC{{O}_{3}}+{{H}_{2}}O$
Adding more carbon dioxide results in the precipitate dissolving to form a colourless solution of calcium hydrogen carbonate. This is used as a test for carbon dioxide. When carbon dioxide is bubbled through limewater the lime water changes from colourless to milky.
From 1st and 2nd point we can conclude that option “C” is correct.

Note: Lime water absorbs carbon dioxide. Drinking lime water improves digestion. Limes are acidic and they help saliva break down food for better digestion.