Question

The density of nitric acid solution is 1.5 g mL\(^{-1}\). Its weight percentage is 68. What is the approximate concentration (in mol L\(^{-1}\)) of nitric acid? (N = 14 u; O = 16 u; H = 1 u)

• A. \( 14.2 \)
• B. \( 11.6 \)
• C. \( 18.2 \)
• D. \( 16.2 \)

Hint:

To determine molarity from weight percentage and density: 1. Multiply the density by 1000 to get total mass per liter. 2. Use the weight percentage to find the mass of solute. 3. Divide by the molecular weight to get molarity.

Answer 1

The Correct Option is D

The density of the nitric acid solution is given as 1.5 g/mL, with a weight percentage of 68% HNO\(_3\). Our task is to find the molar concentration in mol/L.

First, calculate the mass of HNO\(_3\) in 1 L (1000 mL) of solution:

\( \text{Mass of solution} = \text{density} \times \text{volume} = 1.5 \, \text{g/mL} \times 1000 \, \text{mL} = 1500 \, \text{g} \)

\( \text{Mass of HNO}_3 = 0.68 \times 1500 \, \text{g} = 1020 \, \text{g} \)

Given: Molar mass of HNO\(_3\):

\( \text{Molar mass of HNO}_3 = (1 \times 1) + (1 \times 14) + (3 \times 16) = 63 \, \text{g/mol} \)

Calculate the number of moles of HNO\(_3\):

\( \text{Moles of HNO}_3 = \frac{1020 \, \text{g}}{63 \, \text{g/mol}} = 16.190 \, \text{mol} \)

Calculate the concentration in mol/L:

\( \text{Concentration} = \frac{\text{Moles of HNO}_3}{\text{Volume in L}} = \frac{16.190 \, \text{mol}}{1 \, \text{L}} \approx 16.2 \, \text{mol/L} \)

Thus, the approximate concentration of nitric acid is \(16.2 \, \text{mol/L}\).

Answer 2

Here's how to calculate the concentration: 

1. Mass of nitric acid in 1 L of solution:
   Density = 1.5 g/mL = 1500 g/L
   Weight percentage of nitric acid = 68%
   Mass of nitric acid = (68 / 100) × 1500 g = 1020 g
2. Moles of nitric acid:
   Molar mass of HNO₃ = 1 + 14 + (3 × 16) = 63 g/mol
   Moles of nitric acid = mass / molar mass = 1020 g / 63 g/mol = 16.19 mol
3. Concentration of nitric acid:
   Concentration = moles / volume = 16.19 mol / 1 L = 16.19 mol/L ≈ 16.2 mol/L

Therefore, the approximate concentration of nitric acid is 16.2 mol L⁻¹.