Question

1. A mixture is 15 mol% Benzene, 40 mol% Toluene and 45 mol% Xylene. Calculate the mass fraction of each compound. What is the average molecular weight of the mixture? What would be the mass (kg) of a sample containing 250 kmol of Toluene ? (20 points) Benzene (C6H6) – 78.11 g/mol Toluene (C7H8) – 92.13 g/mol Xylene (C8H10) – 106.16 g/mol

Answer 1

Let us assume 100 mole basis, it will have no effect on calculations:

So, moles of Benzene = 15 mol

  moles of Toluene = 40 mol

  moles of Xylene = 45 mol

mass of Benzene = molecular mass * moles = 78.11 g/mol * 15 mol = 1171.65 g

mass of Toluene = molecular mass * moles = 92.13 g/mol * 40 mol = 3685.2 g

mass of Xylene = molecular mass * moles = 106.16 g/mol * 45 mol = 4777.2 g

Total mass = 1171.65 g +3685.2 g + 4777.2 g = 9634.05 g

Mass fraction of Benzene = mass of Benzene / Total mass = 1171.65 g / 9634.05 g = 0.12

Mass fraction of Toluene = mass of Toluene / Total mass = 3685.2 g / 9634.05 g = 0.38

Mass fraction of Xylene = mass of Xylene / Total mass = 4777.2 g / 9634.05 g = 0.50

Average molecular mass of mixture = mole fraction of Benzene * molecular mass of benzene + mole fraction of Toluene * molecular mass of Toluene + mole fraction of Xylene * molecular mass of Xylene

Average molecular mass of mixture = 0.15 * 78.11 g/mol + 0.40 * 92.13 g/mol + 0.45 * 106.16 g/mol

= 11.72 g/mol + 36.86 g/mol + 47.77 g/mol

Average molecular mass of mixture = 96.35 g/mol

Moles of Toluene = 250 kmol , molecular mass of toluene = 92.13 g/mol or 92.13 kg/kmol

Mass of sample containing toluene = Moles of Toluene * molecular mass of toluene

= 250 kmol * 92.13 kg/kmol

Mass of sample containing toluene = 23032.5 Kg