Chapter 16, Problem 16.56SP

Interpretation Introduction

Interpretation:

Determination of the base equilibrium constant for weak base.

Concept introduction:

• With the concept of acid base behaviour of different substances, the concentration of various ionic species present at equilibrium in their aqueous solution can be determined. For this purpose we have to consider the different equilibrium processes involved in such solutions. From this and other considerations we may obtain as many independent equations which may lead to obtain the unknown quantitates, very often introducing simplifications and approximations based on chemical intuition.
• Dissociation or equilibrium constant:The dissociation or equilibrium constant in acid bases arise due to the partial dissociation of weak acid and base. The equilibrium established between the dissociated and un-dissociated part of acid or base is expressed by the equilibrium constant ( $K_a$ ). The concept of $K_a$is immaterial for the strong acid and base as in solution they remain in fully dissociated form.

Given:

Urea behaves as a Lewis base which has two lone pair of electrons on −O atom

that can easily take proton from an acid.The equilibrium constant for the neutralisation of lactic acid ( $C_3{H}_6{O}_3$ ) and urea ( $C{H}_4{N}_{2}O$ ) is $2.1\times {10}^{-4}$. The $K_a$ for lactic acid is $8.3\times {10}^{-4}$.

To determine:

The base dissociation constant ( $K_b$ ) of urea.