A solution made by dissolving 346 g of an unknown compound i

A solution made by dissolving 3.46 g of an unknown compound in 85.0 g of benzene froze at 4.13 °C. What is the molar mass of the compound?

and

alsoA mixture is prepared that is 5.0% (w/w) of an unknown substance mixed with naphthalene (molar mass = 128.2 g mol^-1). The freezing point of this mixture is found to be 77.3 °C. What is the molar mass of the unknown substance? (The melting point of naphthalene is 80.2 °C and K_f = 6.9 °Cm^-1.)

Solution

freezing point of pure benzene = 5.5 ÂÂ °C

delta T = 5.5 - 4.13 =1.37
kf for benzene = 5.12

delta T = m x kf

1.37 = m x 5.12

m = molality of the solution = 0.268 = moles solute / 0.0850 Kg

moles solute =0.0220

molar mass = 3.46 g / 0.0220 mol=157.1 g/mol