Question

How can I calculate the molality when 75.0 grams of MgCl2 is dissolved in 500.0 g of solvent?

Answer 1

The molality of a solution is calculated by taking the moles of solute and dividing by the kilograms of solvent.

molality = number of moles of solute/ mass of solvent in kg

Mass of solvent = 500 g or 0.500 kg

number of moles of Mg`Cl_2` = mass of Mg`Cl_2` / molar mass of Mg`Cl_2`

number of moles of Mg`Cl_2` = 75 g / 95.2 g `mol^-1`

number of moles of Mg`Cl_2`= 0.78 moles

molality = 0.78moles / 0.5 kg

molality = 1.56 mol `kg^-1`