Question

Four monobasic acids a, b, c, and d have the values as $–11.5,–7.5,–12.4$ and $–8.9\mathrm{kcal}{\mathrm{mol}}^{-1}$. when they are neutralized by a common base the acidic character or base of the order

Answer 1

Effect of acid strength on the enthalpy of neutralization;

1. The enthalpy of neutralization $\left(\mathrm{\Delta Hn}\right)$ is the change in enthalpy that occurs when one equivalent of an acid and a base undergo a neutralization reaction to form water and salt.
2. The strength of an acid is determined by the amount of hydrogen ions present for every mole of acid dissolved in water.
3. The stronger the acid the greater the amount of hydrogen ions present in the solution, and hence the more alkali that should be required to neutralize the solution, and therefore enthalpy of neutralization increases with the increase in strength of the acid (so basic character decreases).

The descending order of acidic and basic character ;

1. Converting the given values to kJ by multiplying the enthalpy value by multiplying the energy value by $4.184$that is,

$$\begin{gathered} \mathrm{a}=∆\mathrm{Hn}=-11.5\mathrm{kcal}{\mathrm{mol}}^{-1}\times 4.184=-48.116\mathrm{kJ} \\ \mathrm{b}=∆\mathrm{Hn}=-7.5\mathrm{kcal}{\mathrm{mol}}^{-1}\times 4.184=-31.38\mathrm{kJ} \\ \mathrm{c}=∆\mathrm{Hn}=-12.4\mathrm{kcal}{\mathrm{mol}}^{-1}\times 4.184=-51.88\mathrm{kJ} \\ \mathrm{d}=∆\mathrm{Hn}=-8.9\mathrm{kcal}{\mathrm{mol}}^{-1}\times 4.184=-37.23\mathrm{kJ} \end{gathered}$$

2. From the given data, the acidic character in descending order is given by $c>a>d>b$

3. The basic character in descending order is given by $b>d>a>c$.

Therefore, the acidic character in descending order is given by $c>a>d>b$ and the basic character in descending order is given by $b>d>a>c$.