Question

determine the mass in grams of pentane that must be added to 49g of benzene to make a 1.86 m solution.

Answer 1

Solution :-

given molality = 1.86 m

mass of benzene = 49 g * 1 kg / 1000 g = 0.049 kg

molality = moles / kg solvent

moles of pentane = molality * kg solvent

                                 = 1.86 mol per kg * 0.049 kg

                                 = 0.09114 mol pentane

now lets convert moles of pentane to its mass

mass = moles * molar mass

molar mass of pentane [C5H12] = 72.15 g per mol

lets put the values in the formula

mass of pentane = 0.09114 mol * 72.15 g per mol

                               = 6.58 g pentane

Theerefore mass of the pentane needed = 6.58 g