How to calculate the molar mass?

How to calculate molar mass of substance using freezing point?

• A solution of 2.00g of para-dichlorobenzene in 50.0g of cyclohexane freezes at 1.05(C). What is the molar mass of this substance? A little help please, Thanks

• Answer:

  delta t = m x Kf in this case Kf for the solvent cyclohexene is 20 ; normal freezing point = 6.5 degrees C m = 6.5 - 1.05 / 20= .2725 moles of solvent / kg of solvent we also have 2 g of solute in 50 g of solvent = 2 x 1000/ 50 g / kg = 40 g / kg in 1kg of solvent we have .2725 moles of solute = 40g mass of 1 mole = 40 / .2725 = 146.8 g / mole there is your correct molar mass