1)If 746.4 g of a substance is dissolved in 1723 g of benzene solvent, the freezing point of the solution is -9.19 oC. Calculate the apparent molar mass (g/mol) of substance.
2)
What mass ( g ) of the solvent water should be mixed with 0.008595 L of the solute ethylene glycol to prepare a solution that is 0.212 m ethylene glycol.
1) delta T = Kf*molality
Use this formula to determine molality.
Then molality = moles/kg solvent will determine moles.
Then moles = g/molar mass will determine molar mass.
2)Remember the definition of molality = mols solute/kg solvent. You will need the density of ethylene glycol to convert L in the problem to grams and the molar mass to convert to moles.
To calculate the apparent molar mass of the substance in question 1, we need to use the formula ΔT = Kf * m, where ΔT is the change in freezing point, Kf is the cryoscopic constant, and m is the molality of the solution.
Given:
Mass of substance (m1) = 746.4 g
Mass of solvent (m2) = 1723 g
Freezing point depression (ΔT) = -9.19 oC
First, we need to find the molality (m) of the solution. Molality is defined as the number of moles of solute per kilogram of solvent (mol/kg). To calculate the molality, we need to convert the masses of the substance and solvent to moles:
Moles of substance = mass of substance / molar mass of substance
Moles of solvent = mass of solvent / molar mass of benzene
Since the moles of solvent can be considered equal to the moles of the solution, we can assume that:
Moles of solvent = Moles of solution
Next, we can find the molality (m):
m = Moles of solute / Mass of solvent (in kg)
Finally, we can calculate the apparent molar mass (M) of the substance:
M = Mass of substance / (Moles of solute / Mass of solvent)
To calculate the mass of the solvent in question 2, we can use the formula:
Mass = Volume * Density
Given:
Volume of solute (V) = 0.008595 L
Molarity of solution (M) = 0.212 m
First, we need to calculate the number of moles of ethylene glycol:
Moles of solute = Molarity * Volume
Next, we need to convert the volume of solute (in liters) to mass (in grams). To do this, we need to know the density of the solute. The density of ethylene glycol is approximately 1.113 g/mL.
Convert the volume to milliliters:
Volume = 0.008595 L * 1000 mL/L = 8.595 mL
Calculate the mass of solute:
Mass of solute = Volume * Density = 8.595 mL * 1.113 g/mL
Finally, we can calculate the mass of the solvent water:
Mass of solvent = Mass of solution - Mass of solute