Quinine is a natural product extracted from the bark of the cinchona tree, which is native to south america. quinine is used as an antimalarial agent. when 3.28 g of quinine is dissolved in 25.0 g of cyclohexane, the freezing point of the solution is lowered by 8.43 °
c. the freezing point and kf constant for cyclohexane can be found here.
calculate the molar mass of quinine.

For the answer to the question above, The formula for freezing point depression is 
ΔTf = mkfi 

kf is the freezing point constant 
i is the Van't Hoff factor which in this case is 1 
m is molality (moles of solute/kg of solvent) 
ΔTf is temperature change 

ΔTf is 2.17 °C, the molality is the amount of solute Quinine 
in the solvent cyclohexane. We cannot calculate moles therefore we need to substitute moles with g/mm. 

moles = g/mm so molality=(g/mm)/kg 
molality = (0.845/mm)/0.025 = 33.8/mm 

2.17 = 33.8/mm(20.8) rearrange 

mm = (33.8/2.17)(20.8) = 324g/mol

Outermost (valence) electrons