Molar Mass of Non-Dissociating Solid & Ethylene glycol

[dieteticmajor13]

I just need help setting up these 2 problems.  They aren't explained well in the book or notes.  Thank you!!


1. What is the molar mass of a non-dissociating solid if 9.01 g dissolved  37.3 g or cyclohexane freezes at -1.39 deg-C?  The freezing point of pure cyclohexane is 6.50 deg-C and the freezing point depression constant Kfp is -20.00 deg-C/m.


2. Ethylene glycol, C2H4(OH)2 is the main component of anitfreeze.  What mass percentage of ethylene glycol in water must be used to reduce the freezing poing of the mixture to -12.70 deg-C?  (Kfp for water is -1.86 deg-C/m)

[valdorod]

Use the equation for freezing point depression for non-electrolytes
ΔT_f = k_f*m

solve for molality.

Plug in the mass of solvent in kg into the molality equation to solve for moles   m = mol solute/kg solvent

Take the mass of solute and divide by the moles of solute to find molar mass        molar mass = mass solute/mol solute