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V4viet

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Molarity
Molality
Mole Fraction
Mass %
PPM

However, i understand all of this concepts but when it come down to doing the probs for the MCAT..i get confused and can't solve them..how do you guys start solving for these kinds of probs on the mcat.. or what additional review can i do beside EK that'll help my understanding and solving for these kinds of prob on the mcat..thanks for all of your help
 

HippocratesX

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which part confuses u? Molarity and molality are only for liquids. Molarity (moles/Liter); Molality (moles/Kg of solvent). So basically the only difference is you are weighing out the liquid, versus using volume. mass % and mole fraction are usually reserved for solids, but can be used for anything that either has a balanced equation or a molecular formula.

there are lots of different units used, like ppm (parts per million), or millimolar, or Normality, but i dont think u have to worry too much about those. Just memorize molarity, molality, and the others are pretty much self explanatory (mass % is the percentage of mass an element has in a compound, so (grams of element/total grams of everything) times 100 = mass percent)

and mole fraction is the same idea. moles of element/total moles x 100 = mole fraction
 

V4viet

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hey thanks for reply..i just have problem with doing the probs presented..not the concepts themselves..so i was wondering if there are any practice probs or books that i can look over to have a better grasp of it..
 

sehnsucht

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hey thanks for reply..i just have problem with doing the probs presented..not the concepts themselves..so i was wondering if there are any practice probs or books that i can look over to have a better grasp of it..

there are a lot of good problems on the Examkrackers Chem books and the formulas are well laid out. they do need a bit of getting used to to really nail down so just keep on doing problems to gain more comfort with the conepts in problem format. good luck!
 
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