CHEMISTRY 201X: Homework #2 Due : Friday, September 7, 2007 “Complex Stoichiometry” (My apologies, but there is a necessary correction to problem #2b: the yield of solid is 85.00 g .) (1) (5 points) A 0.5000 g sample of an unknown hydrocarbon (compound containing just carbon and hydrogen) was analyzed by thorough combustion and found to produce 1.6477 g carbon dioxide. (a) What is the empirical formula of the hydrocarbon? (b) A mass spectrum of the substance shows the largest mass peaks at 15 amu, 75 amu, 90 amu, 105 amu and 120 amu. What is the molecular formula of this compound? Explain the observed peaks in the spectrum. (2) (10 points) Two natural sources of the toxic element, arsenic, are its sulfide ores, the minerals orpiment (As 4 S 6 ) and realgar (As 4 S 4 ). These minerals are typically found together in a single ore sample. These compounds are used as pigments for paints: realgar is a red pigment; orpiment is a yellow pigment. If each mineral is heated in air, each reacts with oxygen to form
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