Question

What is the concentration in mole fraction of solute of a 1.25M aqueous solution of potassium nitrate, KNO3? The density of the solution is 1.19 g/mL.

Answer 1

Given concentration of KNO3 solution = 1.25 M = 1.25 mol/L

mass of KNO3 = number of moles * molar mass

mass of KNO3 = 1.25 mol * 101.1032 g/mol

Mass of KNO3 = 126.379 g

density of solution = 1.19 g/mL

1.19g of the solution has 1 mL volume

1 mL of solution has mass 1.19 g

1L = 1000mL solution has mass = 1.19 * 1000 = 1190 g

mass of solution = mass of solute + mass of solvent

in this case, mass of solution = mass of KNO3 + Mass of H2O

mass of solvent = mass of solution - mass of solute

mass of H2O = mass of KNO3 solution - mass of KNO3

mass of H2O = 1990 - 126.379

mass of H2O = 1863.621

mole fraction of solute = number moles of solute/(number moles of solute + number of moles of solvent)

mole fraction of KNO3 = 1.25/(1.25 +(1863.621/18))

mole fraction of KNO3 = 0.01193

mole fraction of H2O = 1 - mole fraction of KCl

mole fraction of H2O = 1 - 0.01193 = 0.9881