Notes Sept 3 2013 Registration for exams open later this afternoon on ELC New 20ish questions 75 minutes 15 minute transition time between exam times Formula weight Elements atomic weight Compounds molecular weight Percent composition elemental analysis comes from experiments g element mol element CH4 What is H mass and the C mass C 12 01 H 1 008 12 01 4 032 16 042 C 12 01 16 402 75 H 4 032 16 042 25 Unknown compound 25 H mass 75 C mass sample 100 g 75 g C 25 g H ConcepTest which molecules have the lowest and highest percent composition of oxygen by mass respectively Acetic acid CH3CO2H Carbon monoxide CO Ethylene glycol HOCH2CH2OH C2H4O2 32 60 53 CO 16 28 57 C2H6O2 32 62 52 A acetic acid carbon monoxide B carbon monoxide acetic acid C carbon dioxide ethylene glycol D ethylene glycol carbon monoxide Empirical formula tells you ratio of atoms in the molecule smallest whole number ratio CH2 empirical formula not seen in nature C 2H4 ethane ethylene or C5H10 Molecular formula how many moles are actually in the compound To go from molecular to empirical formula C 2H4 CH2 or C5H10 CH2 To go from empirical to molecular formula you need a molecular weight Law of Multiple Proportions one of two things must be true different molecules have different ratios even if they have the same elements or if they have same elemental formula those formulas represent different structures Ex H2O H2O2 SO3 SO4 ConcepTest Two organic molecules are dimethyl ether CH3OCH3 and ethanol CH3CH2OH Which is most accurate statement about the molecules A Obey Law of Multiple Proportions because they have different structural formulas B Violate Law of Multiple Proportions because they have identical elemental formulas C are not subject to law of multiple proportions because they are organic D This is a trick question so formulas aren t drawn accurately ConcepTest A Roliads antacid has 550 mg of calcium carbonate 110 mg magnesium hydroxide per tablet What is the calcium by mass per tablet Mg 24 3 Ca 40 08 HO 17 01 CO3 60 01 A 220 mg 660 mg 33 3 B 220 mg 550 mg 40 C 367 mg 550 mg 66 7 D 367 mg 660 mg 55 5 E none of these 550 mg CaCO3 110 mg Mg OH 2 660 mg Ca CO3 100 mg 40 of 550 220 mg BONUS 220 mg 2000 mg 0 11 x 100 11 of minimum daily requirement Purity of samples Percent Purity purity mass of pure substance mass of sample x 100 Module 3 Chemical reactions Chemical equations Balancing chemical equations Intro to chemical equilibrium Aqueous solutions Precipitation reactions Acids and bases Gas forming reactions Oxidation reduction reactions Classifying reactions in aqueous solution What topics on exam will be posted