Asolution of 2.00 g of para-dichlorobenzene in 50.0 g
ofcyclohexane freezes at 1.05oc. what is the molarmass
of this substance?

151 g/mol

Explanation:

When a nonvolatile substance is added to a solvent, the freezing point of the solvent is changed, which is called cryoscopy. When temperature change can be calculated by:

ΔT = Kf*W

Where Kf is the molal freezing point constant of the solvent and W is the molality of the solution.

For cyclohexane, Kf = 20.2 °C/molal, and the freezing point is 6.4 °C, so:

6.4 - 1.05 = 20.2 * W

20.2W = 5.35

W = 0.26485 molal

The molality is:

W = m1/m2*M1

Where m1 is the mass of the solute (in g), m2 is the mass of the solvent (in kg), and M1 is the molar mass of the solute. So:

0.26485 = 2.00/0.05M1

0.0132425M1 = 2.00

M1 = 151 g/mol