Question

100 ml of HNO3 solution and 100 ml NaOH solution each having same molarity were mixed. There is liberation of 1.713 kJ of heat. Calculate the molarity of each solution.

Answer 1

The balanced chemical reaction for neutralisation of $\sf{HNO_3}$ and $\sf{NaOH}$ solutions is,

$\leadsto\sf{HNO_3+NaOH\longrightarrow NaNO_3+H_2O,\quad\!\Delta H^{\Theta}=-55.84\ kJ}$

If $\sf{1.713\ kJ}$ heat energy is liberated, we consider the reaction.

$\leadsto\it{n}\,\sf{HNO_3}+\it{n}\,\sf{NaOH}\longrightarrow \it{n}\,\sf{NaNO_3}+\it{n}\,\sf{H_2O,\quad\!\Delta H=-55.84}\it{n}\ \sf{kJ=-1.713\ kJ}$

We get,

$\longrightarrow\it{n}=\sf{\dfrac{-1.713}{-55.84}=0.031}$

Now,

• No. of moles of $\sf{HNO_3=0.031\ mol}$

• Volume of $\sf{HNO_3}$ solution $\sf{=0.1\ L}$

Hence molarity of $\sf{HNO_3}$ solution is,

$\longrightarrow\sf{M=\dfrac{0.031}{0.1}=0.31\ M}$

Given that molarity is same for each solution.

Hence molarity of each solution is equal to $\bf{0.31\ M}.$