Volumes of 50 ml of 1 M-NaOH and 50 ml of 1 M-HCl both at the same temperature were mixed in a calorimeter of very small heat capacity. A temperature rise of 6.85 K was recorded. In a second experimen

Question

Volumes of 50 ml of 1 M-NaOH and 50 ml of 1 M-HCl both at the same temperature were mixed in a calorimeter of very small heat capacity. A temperature rise of 6.85 K was recorded. In a second experiment, the HCl was replaced by 50 ml of 1 M-CH 3 COOH. The temperature rise was 5.85 K. The enthalpy of ionization (in kcal/mol) of CH 3 COOH is

TestHub · Accepted Answer

Same setup, so heat evolved per mole is proportional to ΔT. Strong acid: ΔH neut = -13.7 kcal/mol; for CH 3 COOH the observed value is -13.7 × 5.85/6.85 = -11.7 kcal/mol. The shortfall is the energy absorbed in ionizing the weak acid: ΔH ion = -11.7 - (-13.7) = +2.0 kcal/mol. Magnitude = 2 kcal/mol, so the answer is 2.

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