posted by Lauren on .
Caffeine C8H10N4O2, is a stimulant found in a tea and coffee. A sample of the substance was dissolved in 45.0g of choloroform CHCl3 to give a 0.0946m solution. How many grams of caffine were in the sample.
m = molality
molality = m = mols/kg solvent.
mols = g/molar mass.
You have kg and m so use equation 1 to solve for mols.
then go to equation 2, plug in mols and molar mass and solve for grams.
ok i know how to figure out the 2nd equation
45.0g CHCl3(1 mols/118gCHCl3)=.381 mols CHCl3
but how do you get molarity. with kg solvent
You wrote a small m when you posted the question initially. m = molality not molarity.
Look at the definition I wrote above.
m = mols/kg solvent.
m(of caffeine) = mols caffeine/kg solvent
0.0946 = mols caffeine/0.045 kg CHCl3.
mols caffeine = ??
The g caffeine = mols carreine x molar mass caffeine = xx
check my work. (By the way, the molar mass CHCl3, which is not needed, is 119.4).