Question

What is the mole fraction of nitric acid in a(n) 8.46% (by mass) aqueous solution of nitric acid

Answer 1

Answer: The mole fraction of nitric acid is 0.026

Explanation:

We are given:

8.46 % (by mass) of aqueous nitric acid solution

This means that 8.46 grams of nitric acid is present in 100 grams of solution

Mass of water (solvent) = Mass of solution - Mass of solute

Mass of water = 100 - 8.46 = 91.54 g

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$     .....(1)

• For nitric acid:

Given mass of nitric acid = 8.46 g

Molar mass of nitric acid = 63 g/mol

Putting values in equation 1, we get:

$\text{Moles of nitric acid}=\frac{8.46g}{63g/mol}=0.134mol$

• For water:

Given mass of water = 91.54 g

Molar mass of water = 18 g/mol

Putting values in equation 1, we get:

$\text{Moles of water}=\frac{91.54g}{18g/mol}=5.09mol$

Mole fraction of a substance is given by:

$\chi_A=\frac{n_A}{n_A+n_B}$

For methanol:

$\chi_{\text{(nitric acid)}}=\frac{n_{\text{(nitric acid)}}}{n_{\text{(water)}}+n_{\text{(nitric acid)}}}

$

$\chi_{\text{(nitric acid)}}=\frac{0.134}{0.134+5.09}\\\\\chi_{\text{(nitric acid)}}=0.026$

Hence, the mole fraction of nitric acid is 0.026