Question

Sodium bicarbonate is less soluble in water than potassium bicarbonate, it is due to:

• A. low molecular weight of $NaHC{O}_3$ as compared to $KHC{O}_3$
• B. hydrogen bonding, sodium bicarbonate contains a dimeric anionic structure in potassium bicarbonate, anions forman infinite chain
• C. hydrogen bonding, potassium bicarbonate contains a dimeric anionic structure while in sodium bicarbonate, anions form an infinite chain
• D. $KHC{O}_3$ is thermally less stable than $NaHC{O}_3$

Answer 1

The correct option is C hydrogen bonding, potassium bicarbonate contains a dimeric anionic structure while in sodium bicarbonate, anions form an infinite chain

Structure of anion in $NaHC{O}_3\left(N{a}^{+}HC{O}_3^{-}\right)$ and $KHC{O}_3\left(K^{+}HC{O}_3^{-}\right)$ is:

The two oxygen atoms with longer $C-O$ distance are hydrogen bonded in pairs to another $C{O}_3$ group with an $O-H...O$ distance $2.61A$, thus linking two $C{O}_3$ groups so as to form a complex anion. $[H_2{C}_2{O}_4{]}^{-}$.This type of approximately coplanar conjugation of two bicarbonate ions is a new one found in acid carbonates and resembles that of a dimeric carboxylic acid. Thus two $H$ bonds dimer type in $KHC{O}_3$(a) and the chain type in $NaHC{O}_3$(b) as shown in figure.

SO due to the presence of two $H$ bonds dimeric anion $KHC{O}_3$ is more soluble in water as $H_{2}O$ being polar and $H$ bonding in dimeric anion of $KHC{O}_3$ makes it more polar.