Exam 1 mccord

Exam 1 mccord - Version 411 Exam 1 McCord(53215 This...

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Version 411 – Exam 1 – McCord – (53215) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. McCord CH302 This exam is only For McCord’s CH302 class. Water Data on BACK oF Bubblesheet 001 10.0 points A semi-permeable membrane can withstand an osmotic pressure oF 0 . 75 atm. What mo- larity oF aqueous magnesium bromide solution would reach the limit For this membrane? (as- sume RT = 25 L · atm · mol 1 ). 1. 0 . 01 M correct 2. 1 M 3. 0 . 03 mM 4. 0 . 03 M 5. 0 . 01 mM Explanation: Use the Formula For osmotic pressure. Re- member that magnesium bromide will disso- ciate into 3 particles, so there will be a Van’t Ho± Factor oF 3 For this calculation. 002 10.0 points What is the osmotic pressure oF a solution that contains 4.56 × 10 3 moles oF lactose in 100 mL oF solution at M 25 C? 1. 111.5 torr 2. 71 torr 3. 848 torr correct 4. 536 torr 5. 165.6 torr Explanation: n = 4 . 56 × 10 3 mol V = 100 mL T = 25 C + 273 = 298 K M = p 456 × 10 3 mol 100 mL Pp 1000 mL L P = 4 . 56 × 10 2 mol L Osmotic pressure π = M R T = ( 4 . 56 × 10 2 mol / L ) × p 0 . 082 L · atm K · mol P (298 K) × p 760 torr 1 atm P = 844 torr 848 torr 003 10.0 points The vapor pressure oF a liquid at 25 C is 200 torr. IF the pressure over the liquid is lowered to 190 torr at 25 C, the liquid will 1. evaporate. 2. Freeze. 3. boil. correct Explanation: Vaporization occurs when the vapor pres- sure oF a liquid is less than the pressure oF the liquid. Boiling occurs when the vapor pressure equals that oF the pressure over the liquid. In this case the vapor pressure exceeds the pressure over the liquid, so boiling will occur. 004 10.0 points What is the boiling point elevation oF a solu- tion oF Na 2 SO 4 (142.1 g/mol, complete disso- ciation) made by dissolving 10.0 g oF Na 2 SO 4 into 250 g water ( K b = 0.512 C/ m )? 1. 0.288 C 2. 0.108 C 3. 0.144 C

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Version 411 – Exam 1 – McCord – (53215) 2 4. 0.576 C 5. 0.363 C 6. 0.432 C correct Explanation: m Na 2 SO 4 = 10.0 g m water = 250 g MW Na 2 SO 4 = 142.1 g/mol m = 10 142 . 1 0 . 25 = 0 . 2815 m m (ideal) = (3)(0 . 2815) = 0 . 844 m because 3 ions formed. Thus Δ T = (0 . 512)(0 . 844 m ) = 0 . 432 C 005 10.0 points Consider two liquids A and B. The vapor pressure of pure A (molecular weight = 50 g/mol) is 225 torr at 25 C and the vapor pressure of pure B (molecular weight = 75 g/mol) is 90 torr at the same temperature. What is the total vapor pressure at 25
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Exam 1 mccord - Version 411 Exam 1 McCord(53215 This...

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