Question

Mole fraction to molality. Convert 0.1538 mole fraction of propanol (C₃H₈O) in water to molality. (Hint: begin by assuming 1 mole total and determine the contributing moles of propanol and contributing moles of water.) Answer to 4 significant figures with appropriate units.

Answer 1

Answer – We are given, mole fraction of propanol = 0.1538

We assume the total mole = 1

We know the mole fraction sum is always 1

So, mole fraction of water = 1-0.1538

                                           = 0.8462

We also know the

Mole fraction = moles / total moles

So, moles of propanol = mole fraction * total moles

                                     = 0.1538 * 1 mole

                                     = 0.1538 moles

Moles of water = 0.8462 *1 mole

                         = 0.8462 moles

Mass of water = 0.8462 moles * 18.015 g/mol

                        = 15.24 g

So the molality of propanol = 0.1538 moles / 0.01524 kg

                                             = 10.10 m