Exam 1 Wed sept 14 199991 elab

# Exam 1 Wed sept 14 199991 elab - Exam 1 Wed special code...

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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 special code...

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