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03/10/2021 12:49 pm
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The enthalpy of neutralisation of a weak acid in 1 M solution with a strong base is -56.1 kcal mol-1. If the enthalpy of ionisation of acid is 1.5 kcal mol-1 and enthalpy of neutralisation of the strong acid with a strong base is -57.3 kJ eq-1. What is the % ionisation of the weak acid in molar solution (assume the acid is monobasic)
(a) 25
(b) 20
(c) 15
(d) 10
1 Answer
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03/10/2021 12:55 pm
Correct answer: (b) 20
Explanation:
The enthalpy of ionisation of weak acid is given by
ΔHion(HA)
= ΔHN(weak acid / strong base) – ΔHN(strong acid/strong base)
= -56.1 - (-57.3) = 1.2 1 kJ mol-1
ΔH(ionisation) = 1.5 1 kJ mol-1
Hence % ionisation in 1 M solution
= \(\frac{(1.5 - 1.2)}{1.5}\) x 100
= 20%