Exam 1 Wed sept 14 199991 elab

Exam 1 Wed sept 14 199991 elab - Exam 1 Wed sept 14 2011...

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Exam 1 Wed sept 14 2011 special code 199991 Elaboration Notice that this is the 199991 version. For the 822228 version the difference is mostly in the position of the answers, except for the true/false questions. They may be a little different . This did result in different average scores at times, but I compensated for that during curving. 1. Please bubble in and write in only the following three items before answering any questions: * THE ABOVE CODE under special codes (without that you will likely have a very, very bad grade) * yourLastName_yourFirstName (single space in between, no middle initials, write double names as one name) * yourStudentIDnumber *NOTHING ELSE 2. Please put your test paper on the correct pile . (without that you will likely have a very, very bad grade) 3. Please read through the questions first and start with the easier ones. 4. Please do write on your white paper. Please write name and ID# on white paper and return it. 5. Please work out your answer on paper first , then copy your answer to the bubble sheet 6. Please select the (most) correct option , unless the question tells you to do otherwise. 7. PLEASE ONLY FILL IN ONE BUBBLE (the machine cannot read two at once). For some questions there may be two correct answers. If so, you’ll get full credit for either one that you pick. 8. Please do answer all questions. Leave ones you do not know open till the end. Then do an educated guess. Blank answers are automatically wrong. (There were still a few people with blank answers. Please do not do that to yourself. 9. If you get nervous, just think of all those other students who have gone through this before you. I have never had a fatality so far…
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Question 1 John exposes 2.54 grams of mercuric oxide, a red powder, to 1000 o C upon which it decomposes into the elements. Ah, Lavoisier’s old experiment! Let ’s hope John was more careful with these dangerous fumes than Lavoisier who did not know they were pretty poisonous . He traps the hot vapors in a cylinder that already contains 1 liter of argon gas at 0 o C and 1 atmosphere pressure. The volume of the cylinder first expands considerably as the injected gases are hot, but once its temperature returns to 0 o C John reads off a value for the volume that is increased only slightly. There are also silvery droplets of a metal on the bottom of the cylinder. ( Hint : First write a balanced reaction equation. 1 mole of gas at 0 o C and 1atm has a volume of 22.4 L. The density of mercury is 13.4 g/mL ). Being good chemists, write the equation first. Mercuric oxide is HgO –a s you knew from the recitation- 2 HgO => 2 Hg + 1 O 2 Molar mass for HgO is 200+ 16 = 216 [g/mole]. As both HgO and Hg have the same coe f ficient we should get 200 .59 /216 .59 *2.54= 2.35 grams of Hg. Dividing by density we get 2.35/13.4 = 0.17 mL = 0.0017 liters of liquid mercury, a tiny value . So B is true There is 2.54/216 = .0127 moles of HgO . Number of moles of O2 is half that: 0.00635, resulting
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Exam 1 Wed sept 14 199991 elab - Exam 1 Wed sept 14 2011...

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