Calculate the percent by mass? using molality

[Craftylikeafly]

A solution of caffeine (C8H10N4O2) in chloroform (CHCl3) as a solvent has a concentration of 7.10*10^-2m.

I know that i have to convert the molality to grams somehow to get the mass of the solute but i am stuck, please help with detail, i also know the m=mols of solute/kg of solvent, caffeine is the solute and the chloroform is the solvent and the mass %= mols of solute/total mass*100


 

[Black Mage]

Have you tried assuming a given amount of solvent?

EDIT: I would double check your % mass formula.

[Craftylikeafly]

I still dont understand 

[Black Mage]

Assume 1kg of chloroform is the solvent.

Molality = (mol of solute) / (kg of solution)

So now you should have mol of solute. Use stoichiometry from there to get the mass of caffeine in this solution.

% Mass = (Mass of solute) / (Mass of Solute + Mass of Solution)

Remember we assumed a mass of solution in the first step.

Hopefully this is more helpful.