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).
To find the number of grams of caffeine in the sample, we need to use the concept of molality. Molality (m) is defined as the number of moles of solute divided by the mass of the solvent in kilograms.
The molality (m) of the caffeine solution is given as 0.0946m or 0.0946 moles of caffeine per kilogram of solvent.
First, we need to convert the given mass of chloroform into kilograms. Since the mass of chloroform is given as 45.0 grams, we divide it by 1000 to convert it into kilograms:
Mass of chloroform (CHCl3) = 45.0 g = 0.045 kg
Now we know the molality of caffeine and the mass of the solvent, we can now calculate the moles of caffeine in the solution using the molality formula:
Molality (m) = Moles of solute / Mass of solvent (in kg)
Rearranging the formula, we have:
Moles of solute = Molality × Mass of solvent
Moles of solute = 0.0946 mol/kg × 0.045 kg
Moles of solute = 0.004252 mol
Now, we can convert the moles of caffeine to grams by multiplying by the molar mass of caffeine, which is 194.19 g/mol:
Grams of caffeine = Moles of solute × Molar mass of caffeine
Grams of caffeine = 0.004252 mol × 194.19 g/mol
Grams of caffeine ≈ 0.826 g
Therefore, there are approximately 0.826 grams of caffeine in the sample.