Molality is a unit of concentration that expresses the number of moles of solute per kilogram of solvent. To calculate the molality of a solution, we need to know the amount of solute and solvent in the solution.
In this problem, we are given that 35.0 grams of MgCl2 is dissolved in 200.0 grams of solvent. We need to first convert the amount of MgCl2 to moles:
Molar mass of MgCl2 = 24.31 g/mol (Mg) + 2 * 35.45 g/mol (Cl) = 95.21 g/mol
Number of moles of MgCl2 = 35.0 g / 95.21 g/mol = 0.3677 mol
Next, we need to convert the mass of solvent to kilograms:
Mass of solvent = 200.0 g = 0.2 kg
Now we can calculate the molality of the solution using the formula:
Molality = number of moles of solute / mass of solvent in kilograms
Molality = 0.3677 mol / 0.2 kg = 1.8385 mol/kg
Therefore, the molality of the solution is 1.8385 mol/kg.