What are the molal concentrations, and mole fractions, of a #385*mg# mass of #C_26H_46O# dissolved in #40*mL# of chloroform?

1 Answer
Jun 28, 2017

Answer:

#"Molality"# #=# #0.0249*mol*kg^-1#

Explanation:

#"Molality"# #=# #"Moles of solute"/"Kilograms of solvent"#

And here, #"molality"# #=# #((0.385*g)/(386.67*g*mol^-1))/(0.040*kg)=0.0249*mol*kg^-1#.

On the other hand, the mole fraction, #chi#, is dimensionless, and this is defined by the quotient.........

#chi_"solute"="Moles of solute"/"Total number of moles in solution"#

So here.........

#chi_"cholesterol"=("Moles of cholesterol")/("Moles of cholesterol+moles of chloroform")#

#=((0.385*g)/(386.67*g*mol^-1))/((0.385*g)/(386.67*g*mol^-1)+(40*g)/(119.38))=2.96xx10^-3#

And #"NECESSARILY"# #chi_"chloroform"=1-chi_"cholesterol"=0.997#

Why #"necessarily?"#