A solution was made by dissolving 10.0g of a nonvolatile nonelectrolyte compound in 100.0g of water froze at -0.93C. What is the approximate molecular weight of the substance. (for water..kf=1.86C/m) (m is molality)
delta T = Kf*m
Solve for m
m = moles/kg solvent
Solve for moles.
moles = grams/molar mass
Solve for molar mass.
To find the approximate molecular weight of the substance, we can use the equation:
ΔT = i * Kf * m
Where:
ΔT = Change in freezing point
i = Van't Hoff factor (1 for non-electrolytes)
Kf = Freezing point depression constant for the solvent (in this case, water)
m = Molality of the solution
Given that the freezing point depression, ΔT, is -0.93°C, and the molality, m, is defined as the number of moles of solute per kilogram of solvent, we can start by calculating the molality of the solution:
molality (m) = moles of solute / mass of solvent (in kg)
The mass of the solvent (water) is 100.0g, which is equal to 0.1kg.
Now, we can calculate the moles of the solute.
moles of solute = mass of solute / molar mass
The molar mass is the molecular weight of the substance.
We are given that the solute has a mass of 10.0g.
Let's substitute the given values into the equations:
ΔT = i * Kf * m
-0.93 = 1 * 1.86 * m
m = -0.93 / 1.86
m = -0.5 mol/kg
Now, let's calculate the moles of the solute:
moles of solute = mass of solute / molar mass
-0.5 = 10.0 / molar mass
To find the molar mass, we need to rearrange the equation:
molar mass = 10.0 / -0.5
molar mass = -20.0 g/mol
However, the molecular weight (or molar mass) cannot be negative.
Thus, there is most likely an error in the calculations or in the given values. Please double-check the numbers provided and try again.