Question

The heat of neutralisation becomes large if either the acid or the base is weak. If true enter 1 else 0.
A. 0
B. 1

Answer 1

Hint: The in general reaction is $\text{HA}+\text{BOH}\to \text{AB}+{{\text{H}}_{2}}\text{O}$. This reaction is also known as Acid-base reaction. See the factors on which heat of neutralisation depends as it deals with acid and bases which are strong and weak and monoprotic and polyprotic acids and bases also.

Complete step by step answer:
Let us first discuss the heat of neutralisation and then, we will discuss the factors on which it depends:
When one equivalent of a base and one equivalent of an acid that undergo neutralization reaction to form water and a salt causes the change in enthalpy which is called heat of neutralisation $\left( \vartriangle {{\text{H}}_{\text{n}}} \right)$ and also defined as the energy released with the formation of 1 mole of water.

Heat of neutralisation reaction depends on 3 factors:
(1) Quantity of acid and base: As, heat of neutralisation is the amount of heat released on formation of one mole of water. When the quantity of acid and base determines the amount of water formed hence, its moles and enthalpy change. Like, $\text{HCl}+\text{NaOH}\to \text{NaCl}+{{\text{H}}_{2}}\text{O}$ gives only one mole of water but ${{\text{H}}_{2}}\text{S}{{\text{O}}_{4}}+2\text{NaOH}\to \text{N}{{\text{a}}_{2}}\text{S}{{\text{O}}_{4}}+2{{\text{H}}_{2}}\text{O}$ gives two moles of water.

(2) Basicity of the acid and base: Basicity is the number of $\left[ {{\text{H}}^{+}} \right]$ or $\left[ \text{O}{{\text{H}}^{-}} \right]$ ions acid or base gives on ionization. More the number of ions, more will be the moles of hydrogen ions and hydroxide ions which reacts to form water.

(3) Strength of acid and base: Strength means the amount of ions produced by the acid or base. This term comes into consideration when there is weak acid or base as it does not dissociate completely. The heat of neutralisation between weak acid and strong base is always less than $-57\text{ KJmo}{{\text{l}}^{-1}}$ because they are partially decomposed.
The heat of neutralisation is less when acid or base is weak. So, the statement in the question is false.
So, the correct answer is “Option A”.

Note: During the reaction of neutralisation, a small part of the heat released during the formation of water is used to decompose the acid to form hydrogen ions and base to form hydroxide ions. The heat of neutralisation between strong acid and strong base is almost the same $-57\text{ KJmo}{{\text{l}}^{-1}}$ for all the acids and all the bases.