Answer:
0.0505
Explanation:
Step 1: Calculate the masses of solute and solvent
We have a 15.7% by mass nitric acid solution, that is, there are 15.7 g of nitric acid (solute) per 100 g of solution. The mass of water (solvent) is:
m(solution) = m(solute) + m(solvent)
m(solvent) = m(solution) - m(solute)
m(solvent) = 100 g - 15.7 g = 84.3 g
Step 2: Calculate the moles of nitric acid
The molar mass of nitric acid is 63.01 g/mol.
15.7 g × (1 mol/63.01 g) = 0.249 mol
Step 3: Calculate the moles of water
The molar mass of water is 18.02 g/mol.
84.3 g × (1 mol/18.02 g) = 4.68 mol
Step 4: Calculate the mole fraction of nitric acid
[tex]X(HNO_3) = \frac{nHNO_3}{nHNO_3+nH_2O} = \frac{0.249mol}{0.249mol+4.68mol} = 0.0505[/tex]