Question

The enthalpy of neutralization of a weak monoprotic acid ($HA$) in $1M$ solution with a strong base is $-55.95kJ/mol.$ If the unionized acid requires $1.4kJ/mol$ heat for its complete ionization and enthalpy of neutralization of the strong monobasic acid with a strong monoacidic base is $-57.3kJ/mol.$ What is the % ionization of the weak acid in molar solution?

• A. 1.5%
• B. 3.57%
• C. 35.7%
• D. 10%

Answer 1

The correct option is B 3.57%

The ionisation reaction for the acid can be written as;
$HA\to H^{+}+A-;{△}_{r}H=1.4kJ/mol$
Means for one mole ionisation 1.4 kJ energy is required

We know the relationship, when weak acid or base is involved :
$△H_{neutralization}=△H_{ionization}+{△}_{r}Hof(H^{+}+O{H}^{-})$

putting the values from the question we get,
$-55.95=△H_{ionization}-57.3$
$△H_{ionization}for1MHA=1.35kJ/mol$

So , percentage of heat utilized by 1 M acid for ionization
$=\frac{1.35}{1.4}\times 100=96.43$
So, acid is 100 - 96.43 = 3.57 % ionized.