Calculate the concentration of nitric acid in moles per litre in a sample which has a density, 1.41 g mL–1 and the mass per cent of nitric acid in it being 69%.

To calculate the concentration of nitric acid in moles per liter, we need to follow a few logical steps that involve understanding the relationship between density, mass percent, and molarity. Let’s break this down step by step.

Step 1: Understanding Density and Mass Percent

The density of the nitric acid solution is given as 1.41 g/mL, and the mass percent of nitric acid in the solution is 69%. This means that in every 100 grams of the solution, there are 69 grams of nitric acid.

Step 2: Calculating the Mass of the Solution

First, we can find out how much 1 liter (1000 mL) of this solution weighs. Using the density, we can calculate the mass:

• Density = Mass/Volume
• Mass = Density × Volume

Substituting the values:

Mass = 1.41 g/mL × 1000 mL = 1410 g

Step 3: Finding the Mass of Nitric Acid

Now that we know the mass of the solution, we can find the mass of nitric acid in it using the mass percent:

Mass of nitric acid = (Mass percent / 100) × Total mass of solution

Mass of nitric acid = (69 / 100) × 1410 g = 972.9 g

Step 4: Converting Mass of Nitric Acid to Moles

Next, we need to convert the mass of nitric acid to moles. The molar mass of nitric acid (HNO₃) is approximately 63.01 g/mol. We can use the formula:

• Moles = Mass / Molar mass

Substituting the values:

Moles of nitric acid = 972.9 g / 63.01 g/mol ≈ 15.43 moles

Step 5: Calculating Molarity

Molarity (M) is defined as the number of moles of solute per liter of solution. Since we calculated the moles of nitric acid in 1 liter of solution, the molarity is:

Molarity = Moles of solute / Volume of solution in liters

Molarity = 15.43 moles / 1 L = 15.43 M

Final Result

The concentration of nitric acid in the sample is approximately 15.43 moles per liter. This high concentration reflects the strong acidic nature of the solution, which is important in various chemical applications.