Chemistry Challenge: Calculating Percent by Mass of Nitric Acid

How can we calculate the percent by mass of nitric acid in a mixture?

Given a solution of nitric acid and the volume and molarity of sodium hydroxide used for neutralization, how do we determine the percentage of nitric acid by mass in the mixture?

Calculating Percent by Mass of Nitric Acid:

To calculate the percent by mass of nitric acid in the mixture, we need to consider the molarity and volume of the sodium hydroxide solution used to neutralize the acid. The balanced equation for the reaction between sodium hydroxide and nitric acid provides the stoichiometric relationship needed to determine the amount of nitric acid present.

First, we calculate the number of moles of sodium hydroxide used in the neutralization reaction. Given that the molarity of the NaOH solution is 0.453 M and the volume used is 22.2 mL, we find:

moles of NaOH = (0.453 mol/L) × (22.2 mL/1000 mL) = 0.1028 mol

Since the balanced equation shows a 1:1 ratio between NaOH and HNO3, the number of moles of nitric acid in the mixture is also 0.1028 mol.

Next, we calculate the mass of nitric acid in the mixture using its molar mass, which is 63.02 g/mol:

mass of HNO3 = 0.1028 mol × 63.02 g/mol = 6.51 g

To determine the percent by mass of nitric acid in the mixture, we need to consider the total mass of the solution, which includes both the nitric acid and the water it is dissolved in. Assuming a density of 1.00 g/mL for the solution, we find the mass of the solution:

mass of solution = 7.78 g / 1.00 g/mL = 7.78 mL

Therefore, the percent by mass of nitric acid in the mixture is calculated as:

percent by mass = (6.51 g / 7.78 g) × 100% ≈ 83.7%

Thus, the percent by mass of nitric acid in the mixture is approximately 83.7%.