So I am working on Chapter 9 of Kaplan blue book (gen chem)...and I just CANNOT figure these out! Sure, the answers are provided but I didn't understand them. I would like to see if others can work these problems in diff. ways. 1) Given that the molecular weight of ethyl alcohol, CH3CH2OH, is 46, and that of water is 18, how many grams of ethyl alcohol must be mixed with 100mL of water for the mole fraction (X) of ethyl alcohol to be 0.2? answer: 64.4 grams 2) What are the concentrations of each of the ions in a saturated solution of PbBr2, given that the Ksp of PbBr2 is 2.1x10^-6? answer: [Pb^2+] = 8.07e-3M and [Br-]=1.61e-2M For this problem, I can do everything up 2.1e-6 = 4x^3. I am having hard time figuring out for X ... can somebody show the math in solving for X by hand? Of course it's easy to figure it out with a calculator but as ya'll know, it's not allowed... THANKS!!!