chem exam 3 number 3-1

# chem exam 3 number 3-1 - Version 405 Exam 3 McCord(53130...

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Version 405 – Exam 3 – McCord – (53130) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. McCord CH301tt This exam is only For McCord’s Tues/Thur CH301 class. PLEASE carefully bubble in your UTEID and Version Number! 001 10.0 points 2.00 moles oF a gas occupies 62.2 L at a par- ticular temperature and pressure. Its density is 0.900 g/L. The standard molar volume is 22.4 L/mole. What is the molar mass? 1. 12.4 g/mol 2. 28.0 g/mol correct 3. 34.6 g/mol 4. Cannot be determined 5. 10.1 g/mol Explanation: n =2 . 00 mol V =62 . 2L density = 0 . 900 g / L molar volume = 22 . 4L / mole Take density times volume to get weight. Then divide weight by moles to get molar mass. That is, ± 0 . 900 g L ²± 62 . 2L 2 . 00 mol ² =28.0g/mol. 002 10.0 points How many moles oF HCl gas are produced iF 5.00 L oF Cl 2 and excess H 2 are reacted at STP? H 2 +Cl 2 2HCl(g) 1. 8.96 mol 2. 0.223 mol 3. 224 mol 4. 112 mol 5. 0.446 mol correct 6. 0.0112 mol Explanation: V Cl 2 =5.00L At STP we can use the standard molar volume, 22 . 4L mol ,toconvertLo FC l 2 to moles oF Cl 2 : 5 . 00 L × mol 22 . 4L =0 . 223 mol Cl 2 Now calculate moles oF H 2 : ?mo lH 2 =0 . 223 mol Cl 2 × 2mo lHC l 1mo lC l 2 =0 . 446 mol 003 10.0 points IF equal weights oF O 2 and N 2 are placed in separate containers oF equal volume at the same temperature, which one oF the Following is true? 1. Molecules in the oxygen ±ask are moving Faster on the average than the ones in the nitrogen ±ask. 2. The nitrogen molecules have a greater average kinetic energy. 3. None oF these 4. Both ±asks contain the same number oF molecules. 5. The pressure in the nitrogen ±ask is greater than that in the oxygen ±ask. cor- rect Explanation: U P, T

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Version 405 – Exam 3 – McCord – (53130) 2 U N 2 U O 2 = ± T MW N 2 ± T MW O 2 = ² MW O 2 MW N 2 = ± 32 14 =1 . 5 U O 2 ,becausetheN 2 molecules are moving at an average kinetic speed 1.5 times faster than O 2 molecules, and will therefore exert a higher pressure. 004 10.0 points At 25 Cand0 .5atm ,wh ichhastheh ighest vapor pressure in a closed 3 liter container? 1. 2litersofwater 2. They all have the same vapor pressure. correct 3. 2.5 liters of water 4. 2.99 liters of water Explanation: 005 10.0 points A750 .0mLm e ta lbu lbi sF l l edw i th0 .421 go fCH 4 and an unknown mass of NH 3 .I f the total pressure in the bulb is 3.77 atm at 315 C, then how much NH 3 is also in the bulb? 1. 0.996 grams 2. 14.5 grams 3. 0.549 grams correct 4. 0.00713 grams 5. 2.39 grams 6. 0.0323 grams 7. 1.17 grams Explanation: n CH 4 =(0 . 421 g) · mol 16 g =0 . 0263 mol V =750mL=0 . 75 L T =315 C+273=588K Applying the ideal gas law equation, PV = nRT n tot = PV RT = (3 . 77 atm) (0 . 75 L) (0 . 08206 L · atm mol · K )(588K) =0 . 0585995 mol n tot = n NH 3 + n CH
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chem exam 3 number 3-1 - Version 405 Exam 3 McCord(53130...

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