Questions & Answers

Question

Answers

A. \[7.0\]

B. \[8.0\]

C. \[6.0\]

D. \[4.0\]

Answer
Verified

Formula used: ${P^H} = 7 + \dfrac{1}{2}[{P^{{K_a}}} - {P^{{K_b}}}]$

Given:

${K_a} = 1 \times {10^{ - 4}};\,{P^{{K_a}}} = \, - log({K_a}) = - \log ({10^{ - 4}}) = 4 $

$ {K_b} = 1 \times {10^{ - 6}};\,{P^{{K_b}}} = \, - log({K_b}) = - \log ({10^{ - 6}}) = 6 (\because \,log10 = 1) $

Where ${K_a}$ and ${K_b}$ are the dissociation constant of acid and base

We know that

${P^H}$of the solution of a salt of a weak acid and weak base

${P^H} = 7 + \dfrac{1}{2}[{P^{{K_a}}} - {P^{{K_b}}}]$ ………….. (i) (Where ${P^{{K_a}}}$and ${{\text{P}}^{{K_b}}}$are the power of dissociation constant of weak acid and weak base)

Put the value of ${P^{{K_a}}}$and ${{\text{P}}^{{K_b}}}$ in equation (i) then we get

\[

{P^H} = 7 + \dfrac{1}{2}[4 - 6] \\

= 7 + \dfrac{1}{2}[ - 2] \\

{P^H} = 7 - 1 \\

{P^H} = 6 \\

\]

Salt of weak acid and weak base undergoes both cationic and anionic hydrolysis. In cationic hydrolysis it gives a weak base and in anionic hydrolysis it gives a weak acid.

The ionization constant is a measure of acid strength: the higher the Ka value, the greater the number of hydrogen ions liberated per mole of acid in solution and the stronger is the acid. \[Ka,{\text{ }}pKa,{\text{ }}Kb\] and \[pKb\] are most helpful when predicting whether a species will donate or accept protons at a specific pH value. They describe the degree of ionization of an acid or base.