We’re being asked to find the freezing point of a 50.0- mL 1.54 % MgCl2 by mass solution after adding an additional 1.34 gMgCl2 ( i = 2.5 for MgCl2.)
Recall that the freezing point of a solution is lower than the freezing point of a pure solvent.
When calculating the freezing point of a solution, we’re going to use the equation for Freezing Point Depression:
∆Tf = change in freezing point = Tf pure solvent –Tf solution
Kf = freezing point depression constant
i = van' t Hoff factor of the solute = no. of ions
m = molality
We need to find the molality of the solution after adding additional MgCl2 to solve for its freezing point by doing these steps:
Step 1. Determine the composition of the solution after adding MgCl2.
Since we're given the volume and density of the solution, we can determine its mass using the equation:
Also, recall that Mass or weight percent (% by mass) is the percentage of a given element or compound within a solution.
The equation used to calculate for mass percent is shown below:
• Mass component → mass of solute
• Total mass → mass of solution
Step 2. Calculate the moles of the solute.
Step 3. Calculate the molality of the solution.
Solute = MgCl2
Solvent = Water (H2O)
Step 4. Calculate the freezing point of the solution.