Question

Heat of neutralisation of $HF$ (a weak acid) with strong base is $-16.4$ $kcal$.

Calculate heat of ionisation of $HF$ in water.

• A. $-13.7kcal$
• B. $-2.7kcal$
• C. $+30.1kcal$
• D. $+3.01kcal$

Answer 1

The correct option is B $-2.7kcal$

(i) $HF+O{H}^{-}⟶H_{2}O+F^{-};\Delta H=-16.4kcal$

(ii) $H^{+}+O{H}^{-}⟶H_{2}O;\Delta H=-13.7kcal$

From equations (i) - (ii) gives the required equation (ionisation of $HF$ in water)

$HF⟶H^{+}+F^{-};\Delta H=-2.7kcal$