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 is required $1.4kJ/mol$ heat for it's 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. $1$%
• B. $3.57$%
• C. $35.7$%
• D. $10$%

Answer 1

Answer: (B)

$3.57$%

Let x be the percentage ionization of the weak acid in molar solution.
The enthalpy of neutralization of the weak acid is the sum of the enthalpy of neutralization of strong acid and the heat required for the complete ionization of weak acid.
Hence,

$-57.3+1.4\times (1-0.01x)=-55.95$

$1.4\times (1-0.01x)=-55.95+57.3=1.35$

$(1-0.01x)=0.964$

$0.01x=1-0.964=0.0357$

$x=100\times 0.0357=3.57$ %