Chemistry

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

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  1. 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.

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  2. 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

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  3. 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).

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