Question

The species present in solution when $CO _{2}$ is dissolved in water are

• A. $CO _{2}, H _{2} CO _{3}, HCO _{3}^{-}, CO _{3}^{2-}$
• B. $H _{2} CO _{3}, CO _{3}^{2-}$
• C. $CO _{3}^{2-}, HCO _{3}^{-}$
• D. $CO _{2}, H _{2} CO _{3}$

Answer 1

Answer: (A)

Carbon dioxide dissolves in water to form carbonic acid.
$CO _{2}+ H _{2} O \rightleftharpoons H _{2} CO _{3}$
Carbonic acid is a weak acid. It dissociates to form carbonate and bicarbonate ions.
$H _{2} CO _{3}+ H _{2} O \rightleftharpoons HCO _{3}^{-}+ H _{3} O ^{+}$
Bicarbonate ion dissociates to form carbonate ion.
$HCO _{3}{ }^{-}+ H _{2} O \rightleftharpoons CO _{3}{ }^{2-}+ H _{3} O ^{+}$
Hence, the species present in the solution are $CO _{2}, H _{2} CO _{3}, HCO _{3}^{-}, CO _{3}{ }^{2-}$.