Question

Pure water boils at 373 k and pure nitric acid boils at 359 K the azeotropic mixture of water and nitric acid boils at T K. T=??

Answer 1

• The solution of $HN{O}_3$ in water shows negative deviation and a solution that shows large negative deviation from Raoult's law forms a maximum boiling azeotrope at a specific composition. Nitric acid and water is an example of this class of azeotrope.
• This azeotrope combination includes an appropriate composition of 68% nitric acid and 32% water by mass.
• Due to less composition of water T > 359 K ​and we know that the dependency of temperature is intentionally proportional to the solvent part in the azeotropic mixture and in their solution water part is less, that's why T > 359 K.

• At this composition the solution boils at constant temperature without a change in the ​composition, i.e., the liquid phase and vapour phase have same composition.
• Hence, the boiling point of this azeotrope is 393 K.