A solution was made by dissolving 62.07 grams of a compound in 500.0 g of water. The compound was not ionic. The freezing point of the solution was measured and found to be – 1.86oC. Using the Kf value in your textbook , the molar mass of this compound can be calculated to be

a) 57.7 g/mol
b) 124 g/mol
c) 231 g/mol
d) 62.1 g/mol
e) 115 g/mol

bet its e

chemistry - DrBob222, Friday, February 3, 2012 at 6:34pm
If you were betting you lost.
delta T = i*Kf*m
You know dT, i = 1, and Kf. Solve for molality.
Molality = moles/kg solvent.
You have m and kg solvent, solve for moles.

moles solute = n = grams solute/molar mass solute.
You know moles and grams, solve for molar mass.

still lost :(

From Dr. Bob's hints, you have

Δ T = i*Kf*M
where M is the number of moles

ΔT = 1.86 °C
i=1
Kf=1.86 °C/m for non-ionizing solutes (check value from your book)

M=ΔT/(i*Kf) mole

Equate this to the mass of solute per 1000 ml. of solution, which we have to assume that the volume of solution equals the volume of water initially to get

M m/l= 62.07/0.5 g/l.
So molar mass
= (62.07/0.5)/M

To solve this problem, we can use the formula for freezing point depression:

ΔT = i * Kf * m

where:
ΔT is the change in freezing point (in this case, -1.86°C)
i is the van't Hoff factor (the number of particles the compound dissociates into when it dissolves; for a non-ionic compound, i will be 1)
Kf is the cryoscopic constant for water (found in your textbook or reference material)
m is the molality of the solution (moles of solute divided by kilograms of solvent)

We can rearrange the formula to solve for molality:

m = ΔT / (i * Kf)

In this case, we are given the freezing point depression (-1.86°C) and the mass of the solvent (500.0 g). We need to find the molality of the solution.

m = -1.86 / (1 * Kf)

To find the molar mass of the compound, we need to convert the molality to moles. Since we know the mass of the solute (62.07 g), we can use the moles = mass / molar mass equation to solve for molar mass.

moles = 62.07 / molar mass

Rearranging the equation:

molar mass = 62.07 / moles

Therefore, to find the molar mass of the compound, we need to substitute the values we know into the equations and perform the calculations.