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Exam 3-solutions

# Exam 3-solutions - Version 016 – Exam 3 – sutcliffe...

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Unformatted text preview: Version 016 – Exam 3 – sutcliffe – (90830) 1 This print-out should have 23 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 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. 273 g · mol − 1 2. 21 . 6 g · mol − 1 3. 869 g · mol − 1 4. 162 g · mol − 1 correct 5. 50 . 8 g · mol − 1 Explanation: T = 125 ◦ C + 273.15 K = 398 . 15 K P = (175 Torr) 1 atm 760 Torr = 0 . 230263 atm ρ = 1 . 14 g / L The ideal gas law is P V = n RT n V = P R T with unit of measure mol/L on each side. Multiplying each by molar mass (MM) gives n V · MM = P R T · MM = ρ , with units of g/L. MM = ρ RT P = (1 . 14 g / L) ( . 08206 L · atm mol · K ) . 230263 atm × (398 . 15 K) = 161 . 755 g / mol 002 10.0 points Which substance is correctly matched to the type of solid it forms? 1. bromine: ionic 2. copper: network 3. hydrogen sulfide : ionic 4. nitrogen: molecular correct Explanation: Bromine, nitrogen and hydrogen sulfide are molecular solids. Copper is a metallic solid. 003 10.0 points A liquid in a test tube has a curved surface such that the edges touching the glass are higher than the surface at the center. This must mean that the cohesive forces are less than the adhesive forces. 1. True correct 2. False Explanation: This is the typical meniscus shape of wa- ter in glass - a concave shape. The liquid tries to maximize its contact with the glass because the adhesive forces are stronger than the cohesive forces. 004 10.0 points At constant temperature if the volume of a gas sample is tripled the pressure will 1. be tripled. 2. remain the same. 3. be one third the original. correct 4. be increased by a factor of 6. 5. be cut in half. Explanation: 3 V 1 = V 2 Boyle’s Law relates the volume and pressure of a sample of gas: P 1 V 1 = P 2 V 2 P 1 V 1 = P 2 (3 V 1 ) Version 016 – Exam 3 – sutcliffe – (90830) 2 P 1 = 3 P 2 P 2 = 1 3 P 1 005 10.0 points How many carbon atoms are in 4.56 grams of ethanol (CH 3 CH 2 OH). 1. 1 . 19 × 10 23 atoms correct 2. 2.00 atoms 3. 1 . 26 × 10 26 atoms 4. 0.0991 atoms 5. 5 . 97 × 10 22 atoms 6. 3 . 29 × 10 − 25 atoms 7. 6 . 32 × 10 25 atoms 8. 0.198 atoms Explanation: m = 4.56 g ? C atoms = 4 . 56 g C 2 H 6 O × 1 mol C 2 H 6 O 46 g C 2 H 6 O × 2 mol C atoms 1 mol C 2 H 6 O × 6 . 022 × 10 23 C atoms 1 mol C atom = 1 . 19 × 10 23 C atoms 006 10.0 points Calcium metal reacts with water to form cal- cium hydroxide and hydrogen gas. How much hydrogen is formed when 0.50 g of calcium are added to water? 1. 0.025 g correct 2. 0.050 g 3. 0.50 g 4. 0.10 g Explanation: m Ca = 0 . 50 g The balanced equation is Ca + 2 H 2 O → Ca(OH) 2 + H 2 , and indicates the 1 mol H 2 is produced for each mole Ca reacted. First we calculate moles Ca present: ? mol Ca = 0 . 50 g Ca × 1 mol Ca 40 . 1 g Ca = 0 . 0125 mol Ca Since 1 mol H 2 is produced for each mole...
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Exam 3-solutions - Version 016 – Exam 3 – sutcliffe...

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