Calculate the Molality of Nitric Acid in a Concentrated Solution

What is the molality of nitric acid in a concentrated solution of nitric acid (68% HNO3 by mass)?

The molality of a solution is defined as the number of moles of solute per kilogram of solvent. How do we calculate the molality of nitric acid in this concentrated solution?

Answer:

The molality of nitric acid in a concentrated solution of nitric acid (68% HNO3 by mass) is 1.16 mol/kg.

In order to calculate the molality of nitric acid in the concentrated solution, we first need to convert the mass percent of HNO3 to the mole fraction of nitric acid. Since the molar mass of HNO3 is 63.01 g/mol, we can calculate the mass of HNO3 in 100 g of the solution: 0.68 x 100 g = 68 g.

Next, we calculate the number of moles of HNO3 in 68 g by dividing the mass by the molar mass: 68 g / 63.01 g/mol = 1.0809 mol.

Assuming the solution is made up of 1000 g of water, we can calculate the molality by dividing the number of moles of HNO3 by the mass of water in kg: Molality = 1.0809 mol / 0.932 kg = 1.16 mol/kg.