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exam 3 solutions

# exam 3 solutions - Version 048 Exam Three Shear Shear(52375...

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Version 048 – Exam Three: Shear – Shear – (52375) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. DrRuth says: In all cases, select the answer that BEST answers the question asked. The total number of points on this exam is 350. Read the whole thing first and plan which to answer first because you feel confident about them. Notice the harder ones and save them up till last so you don’t use up all your time working on them. Unless otherwise stated, assume the gases in all questions are ideal. Shear 52375 g = 9 . 8 m / s 2 1 atm = 101325 Pa = 760 torr R = 0.08206 L atm K 1 mol 1 R = 0.08314 L bar K 1 mol 1 R = 8.314 J K 1 mol 1 Effusion rate of gas 1 Effusion rate of gas 2 = radicalbigg M 2 M 1 Effusion rate at T 1 Effusion rate at T 2 = radicalbigg T 1 T 2 KE = 2 / 3 RT u rms = radicalbigg 3 RT M 001 20.0 points Calculate the pressure of 4 g of nitrogen gas in a 1 L container at 20.0 C. 1. 96.2 atm 2. 0.235 atm 3. 6.87 atm 4. 3.44 atm correct 5. 0.469 atm Explanation: m = 4 g V = 1 L T = 20 C + 273.15 = 293.15 K For the nitrogen, n = (4 g N 2 ) · 1 mol N 2 28 . 0134 g N 2 = 0 . 142789 mol N 2 P V = n R T P = n R T V = (0 . 142789 mol N 2 ) ( 0 . 08206 L · atm mol · K ) 1 L × (293 . 15 K) = 3 . 43491 atm 002 10.0 points A mixture of CO, CO 2 and O 2 is contained within a 275 mL flask at 0 C. If the total pres- sure is 780 torr, the CO has a partial pressure of 330 torr and the CO 2 has a partial pressure of 330 torr, what is the partial pressure of O 2 ? 1. 330 torr 2. 120 torr correct 3. 660 torr 4. 780 torr 5. 900 torr Explanation: P total = 780 torr P CO = 330 torr P CO 2 = 330 torr P total = P CO + P CO 2 + P O 2 P O 2 = P total - P CO - P CO 2 = 780 torr - 330 torr - 330 torr = 120 torr 003 20.0 points Given the reaction and the solubility informa- tion below, write the net ionic equation for the reaction

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Version 048 – Exam Three: Shear – Shear – (52375) 2 potassium phosphate(aq) + lead(II) nitrate(aq) General solubility guidelines: 1) Most sodium, potassium and ammonium compounds are soluble in water. 2) Most nitrates, acetates and chlorates are soluble. 3) Most chlorides are soluble, except those for silver, mercury(I) and lead. Lead(II) chloride is soluble in hot water. 4) Most sulfates are soluble, except those of barium, strontium and lead. 5) Most carbonates, phosphates and silicates are insoluble, except those of sodium, potassium and ammonium. 6) Most sulfides are insoluble, except those of calcium, strontium, sodium, potassium and ammonium. 1. 2 K 3 PO 4 (aq) + 3 Pb(NO 3 ) 2 (aq) -→ 6 KNO 3 (aq) + Pb 3 (PO 4 ) 2 (s) 2. 2 K 3 PO 4 (aq) + 3 Pb(NO 3 ) 2 (aq) -→ 6 K + (aq) + 6 NO 3 (aq) + Pb 3 (PO 4 ) 2 (s) 3. 3 Pb 2+ (aq) + 2 PO 3 4 (aq) -→ Pb 3 (PO 4 ) 2 (s) correct 4. None of these 5. 6 K + (aq) + 2 PO 3 4 (aq) +3 Pb 2+ (aq) + 6 NO 3 (aq) -→ 6 K + (aq) + 6 NO 3 (aq) + Pb 3 (PO 4 ) 2 (s) Explanation: K 3 PO 4 (aq) + Pb(NO 3 ) 2 (aq) net ionic equation = ? The ionic equation is 6 K + (aq) + 2 PO 3 4 (aq) +3 Pb 2+ (aq) + 6 NO 3 (aq) -→ 6 K + (aq) + 6 NO 3 (aq) + Pb 3 (PO 4 ) 2 (s) and the net ionic equation is 3 Pb 2+ (aq) + 2 PO 3 4 (aq) -→ Pb 3 (PO 4 ) 2 (s) 004 10.0 points Consider the two water molecules O H H O H H A B Which statement is correct?
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