Question

List I and List II contains four entries each. Entries of List I are to be matched with some entries of List II. One or more than one entries of List I may have the matching with the same entries of List II
When we Titrate sodium carbonate solution (in beaker) with hydrochloric acid

Answer 1

(A) At the start of the titration, the solution is basic due to hydrolysis of carbonate ion $C{O}_3^{2-}$.

(B) Before the first equivalence point, the solution contains bicarbonate ion $HC{O}_3^{-}$ and carbonate ion $C{O}_3^{2-}$.
Thus a buffer solution containing carbonate ion $C{O}_3^{2-}$ and bicarbonate ion $HC{O}_3^{-}$ is obtained.

(C) At first equivalent point bicarbonate ion $HC{O}_3^{-}$ is present which is amphiprotic anion.
The pH of the solution is given by the expression $pH=1/2(p{K}_{a_1}+p{K}_{a_2})$

(D) Between the first and second equivalent points, bicarbonate ion $HC{O}_3^{-}$ and carbonic acid $H_{2}C{O}_3$ are present.
Thus, a buffer solution containng bicarbonate ion $HC{O}_3^{-}$ and carbonic acid $H_{2}C{O}_3$ is formed.