This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: Version 241 Exam 3 sutcliffe (52380) 1 This printout should have 28 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points How much 0.100 M H 2 SO 4 are needed to make 25.0 mL of 0.00500 M solution? 1. 500 mL 2. 1.25 mL correct 3. 0.00200 mL 4. 0.800 mL Explanation: M 1 = 0.100 M M 2 = 0.00500 M V 2 = 25 . 0 mL A portion of the 0 . 1 M H 2 SO 4 solution will be diluted with water to form 25 mL of the . 005 M H 2 SO 4 solution. All of the moles of H 2 SO 4 in the new dilute solution must come from the more concentrated solution. (There is no H 2 SO 4 in the water!) We use the desired volume and molarity of the dilute solution to determine the number of moles of H 2 SO 4 needed to make this solution: ? mol H 2 SO 4 = 25 mL soln 1 L soln 1000 mL soln . 005 mol H 2 SO 4 1 L soln = 0 . 000125 mol H 2 SO 4 We need enough of the 0 . 1 M solution to provide 0 . 000125 mol H 2 SO 4 . We use the molarity to convert from moles to volume of the solution: ? mL soln = 0 . 000125 mol H 2 SO 4 1 L soln . 1 mol H 2 SO 4 1000 mL soln 1 L soln = 1 . 25 mL soln 1 . 25 mL of the 0 . 1 M solution diluted to 25 mL with water would give us the desired solution. 002 10.0 points The density of the vapor of allicin, a compo nent of garlic, is 1 . 14 g L 1 at 125 C and 175 Torr. What is the molar mass of allicin? 1. 50 . 8 g mol 1 2. 162 g mol 1 correct 3. 273 g mol 1 4. 869 g mol 1 5. 21 . 6 g mol 1 Explanation: T = 125 C + 273.15 K = 398 . 15 K P = (175 Torr) 1 atm 760 Torr = 0 . 230263 atm = 1 . 14 g / L The ideal gas law is P V = nRT n V = P RT with unit of measure mol/L on each side. Multiplying each by molar mass (MM) gives n V MM = P RT MM = , with units of g/L. MM = RT P = (1 . 14 g / L) ( . 08206 L atm mol K ) . 230263 atm (398 . 15 K) = 161 . 755 g / mol 003 10.0 points Consider the following reaction: 2 FeS + 3 N 2 2 FeN + 2 SN 2 This reaction has a 65.0% yield. Version 241 Exam 3 sutcliffe (52380) 2 How much N 2 is consumed if 13.6 g of FeN are produced? 1. 0.200 mol 2. 31.4 mol 3. 0.190 mol 4. 0.449 mol correct 5. 412 mol 6. 0.150 mol 7. 0.899 mol Explanation: % yield = 65% m FeN = 13 . 6 g 13.6 g FeN is the actual yield. We need to first calculate the theoretical yield. % yield = actual yield theoretical yield theoretical yield = actual yield % yield ? mol N 2 = 13 . 6 g FeN 100 65 1 mol FeN 69 . 86 g FeN 3 mol N 2 2 mol FeN = 0 . 449 mol N 2 004 10.0 points Which of the following statements about dis persion forces is NOT correct? Dispersion forces 1. are also called London forces....
View
Full
Document
This note was uploaded on 10/20/2011 for the course CH 301 taught by Professor Fakhreddine/lyon during the Fall '07 term at University of Texas at Austin.
 Fall '07
 Fakhreddine/Lyon
 Chemistry

Click to edit the document details