Chemical Thermodynamics Question 414
Question: The enthalpy of neutralisation of a weak acid in 1 M solution with a strong base is $ -56.1kcalmo{{l}^{-1}}. $ If the enthalpy of ionisation of acid is $ 1.5kcalmo{{l}^{-1}} $ and enthalpy of neutralisation of the strong acid with a strong base is $ -57.3kJe{{q}^{-1}} $ . What is the % ionisation of the weak acid in molar solution (assume the acid is monobasic)
Options:
A) 25
B) 20
C) 15
D) 10
Show Answer
Answer:
Correct Answer: B
Solution:
- The enthalpy of ionisation of weak acid is given by $ \Delta H_{ion}(HA) $
$ =\Delta H_{N} $ (weak acid / strong base) - $ \Delta H_{N} $ (strong acid / strong base) $ =-56.1-( -57.3 )=1.2kJ,mo{{l}^{-1}} $
$ \Delta {H_{(ionisation)}}=1.5,kJmo{{l}^{\text{-}1}} $
Hence % ionisation in 1 M solution $ =\frac{(1.5-1.2)}{1.5}\times 100=20% $ %
