An aqueous solution of nitric acid contains 70.0 % HNO3 by mass. The density of HNO3 is 1.42 (g/cm3). Express the mass percent of HNO3 in molarity.

[HNO₃] = 15.7 M

Explanation:

70% HNO₃ by mass, means that in 100 g of solution, we have 70 g of solute (in this case our solute is the HNO₃)

Let's determine the volume of solution, by density.

Solution density = Solution mass / Solution volume

1.42 g/mL = 100 g / Solution volume

100 g / 1.42 g/mL = Solution volume → 70.4 mL

This is the volume occupied by the 70 grams of solute.

Molarity is: moles of solute / L of solution

Let's convert the mass to moles like this:

70 g / 63 g/m = 1.11 moles

Let's convert the volume from mL to L

70.4 mL / 1000 = 0.0704L

M = mol/L → 1.11 mol / 0.0704L = 15.7 M