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04/10/2021 1:12 pm
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When 1 mole of oxalic acid is treated with excess of NaOH in dilute aqueous solution, 106 kJ of heat is liberated. Predict the enthalpy of ionisation of the acid
(a) 4.3 kJ mol-1
(b) -4.3 kJ mol-1
(c) 8.6 kJ mol-1
(d) -8.6 kJ mol-1
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04/10/2021 1:19 pm
Correct answer: (c) 8.6 kJ mol-1
Explanation:
H+(aq) + OH-(aq) ⇌ H2O(l);
ΔH = -57.3 kJ ......(i)
H2C2O4 + 2OH- ⇌ C2O4- + 2H2O;
ΔH = -106 kJ ......(ii)
For the second reaction the value should have been 2 × (-57.3) = -114.6 kJ
The difference (114.6 - 106) = 8.6 1 kJ mol-1 is used to effect of the ionisation of oxalic acid.