ThermochemistryHard

Question

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

Options

A.1%
B.3.57%
C.35.7%
D.10%

Solution

HA → H+ + A- ; ᐃrH = 1.4 kJ/mol
ᐃHneutralization = Hionization + ᐃrH of  (H+ + OH- H2O)
- 55.95 = Hionization - 57.3 
Hionization for 1 M HA = 1.35 kJ/mol
% heat utilized by 1 M acid for ionization
= × 100 = 96.43%
So, acid is 100 - 96.43 = 3.57% ionized.

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