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Browse SpacePlease post questions about the course or the material (or something out of curiosity) here using the "Add Comment" button below. Prof. Katz or Rice will answer your question ... also in this space. Feel free to comment or follow up on others questions. (Don't see the "Add Comment" button? Make sure you're logged in.) 
Could you please go over getting the empirical formula from the products in a combustion reaction? (like question 13 on the practice exam)
Posted by Hey, I'll go through #13 in detail at the review session, but briefly: 1) take your mass quantities to moles, 2) identify the molar ratio of water to CO2 to HBr as whole numbers, 2) identify how many C, H, and Br atoms that you need to have on the left side of the equation given the 'balanced' ratio on the right (C=CO2, H=2*H2O+HBr, Br=HBr). Input these atomic quantities into the appropriate subscripts of the unknown's chemical formula and reduce to an empirical formula if necessary.
Like I said, I'll go through it thoroughly on Monday!
For the folks in my section, I would do this one slightly differently (both methods work). 1) convert mass of CO2 and H2O to moles; 2) convert moles CO2 --> moles C atoms --> mass C atoms, and convert moles H2O --> moles H atoms --> mass H atoms; 3) subtract mass of C and H atoms from mass of sample to get the mass of O atoms and then convert to moles O atoms; 4) Now that you have moles C, H, and O, write the formula with the molar quantities as subscripts, and divide through by the smallest value to get the empirical formula (and multiply by a small integer to make the subscripts whole numbers, if needed).
Update regarding #13 on the Practice Exam: For this one, there is only C, H, and Br (no oxygen). You use the same general methods. Moles/atoms of C is found from moles of CO2; moles/atoms of Br is found from moles of HBr; moles/atoms of H is found from BOTH moles of H2O and HBr. You don't have to do any subtraction to find O, since there isn't any O in the compound formula.
Will we need to know about some of the different experiments from chapter 2? Like Millikan's oil drop experiment, or Rutherford's gold foil experiment?
Will we have to know things in the chapter reviews that we didnt discuss at all in lecture, like Coulomb's law or using angstroms to do calculations?
I am looking at question 14 from the practice exam and have some questions. Are we supposed to calculate the standard enthalpy of formation for the given amount (1.1 grams) of propane or for the 1 mole of propane? I am not sure how we would need the mass, pressure and temperature data if it is indeed the latter.
Nevermind... Problem solved. I would still like to go over this in the review for clarity as I tweaked signs to get the right looking answer.
Hi everyone, a question came up in my section about what will need to be memorized for an exam ... while more specific details will follow, know that for the most part, equations and conversion factors will be provided on an examination. You will however, have to know the greek prefixes for the SI units (milli, micro, kilo, etc.). There will be plenty of actual chemistry to memorize soon enough! -Kevin