ENVI 1106 SAMPLE MIDTERM 3 QUESTIONS Questions 1-4 (circle the correct answer): 1. Which of the following would have a density of 0.172 g/L at 7.0°C and 0.987 atm? a) Ne b) O2 c) H2 d) He e) N2 2. Which of the following samples will have the lowest pressure if they are all at the same temperature and in identical containers (same volumes)? a) 15 g CO2 b) 15 g Ne c) 15 g F2 d) 15 g Kr e) All of these samples will have the same pressure. 3. Which of the following will cause the volume of an ideal gas to increase by a factor of 3? a) Raising the temperature from 25°C to 75°C at constant pressure. b) Lowering the absolute temperature by a factor of 3 at constant pressure. c) Raising the absolute temperature by a factor of 3 at constant pressure. d) Lowering the absolute temperature by a factor of 3 while raising the pressure by a factor of 3 e) Raising the pressure by a factor of 3 while the temperature stays constant. 4. What volume (in mL) will a sample of F2 gas occupy in a syringe at 5.5 atm, if the F2 has a volume of 25.0 mL at 1.2 atm? a) 11 mL b) 17 mL c) 3.8 mL d) 5.5 mL e) 7.6 mL Question 5 Consider the following reaction: C3H7SH(l) + 6 O2(g) → 3 CO2(g) + SO2(g) + 4 H2O(g) Molar masses: C3H7SH: 76.16 g/mol O2: 32.00 g/mol CO2: 44.01 g/mol a) What mass (in grams) of CO2 can be produced from combining 43.0 g C3H7SH with 234 g O2? 43.0 g C3H7SH x ( 234 g O2 x ( )x( )x( )x( )= )x( )= 160.9 g CO2 Therefore, C3H7SH is limiting reagent and 74.54 g CO2 are produced. b) If the 38.9 g CO2 is actually produced, what is the percent yield? x 100 = 52.2 % yield 74.54 g CO2 Question 6 4.94 g of H2O2 (l) is heated in a 3.50 L closed reaction vessel until it decomposes completely as follows: 2 H2O2 (l)  O2 (g) + 2H2O (g) (Assume that the temperature remains constant at 250C) a) How many moles of O2(g) and H2O(g) are produced? b) What are the mole fractions of O2(g) and H2O(g) after the reaction? c) Calculate the total pressure and the partial pressures of O2(g) and H2O(g) after the reaction. a) 4.94 g H2O2 x ( )x( ) = 0.07260 mol O2 4.94 g H2O2 x ( )x( )= 0.1452 mol H2O b) Total moles = 0.07260 mol + 0.1452 mol = 0.2178 mol  (O2) = 0.07260/0.2178 = 0.3333  (H2O) = 0.1452/0.2178 = 0.6666 (note: these could have been calculated before doing part (a) ) c) Total pressure: P = = ( )( PO2 = (0.3333)( 2.671 atm) = 0.890 atm PH2O = (0.6666)( 2.671 atm) = 1.78 atm )( ) = 2.671 atm Question 7 Indicate the chiral carbons in the following compound with a star (*): * * * Question 8 Name the following compounds. 3-ethyl-3-methyl-hexane 1,3-dimethylpentane 3-ethyl-3-methyl-1-hexene 2-methyl-1-pentyne Question 9 Which of the following names is correct? a) 1,2-dimethylhexane b) 1-methylnonane c) 4,5-diethylpentane d) 2-methyl-3-propylheptane e) None of the above names are correct. Question 10 Which of the following names is correct? a) 2-methyl-1-butene b) 3,3-diethyl-4-butene c) 2-ethyl-3-pentene d) 1-propyl-2-pentene e) None of the above is correct. Question 11 Write balanced chemical equations for the following, drawing STRUCTURES for all reactants and products (line skeleton structures or structural formulas are acceptable): a) The reaction of 3-ethyl-2-methylhexane with Br2 in the presence of light. b) The addition of Cl2 to 3,4-dimethylcyclohexene. c) The catalytic hydrogenation (addition of H2) to 4-isopropyl-trans-2-decene Question 12 Which of the following compounds exhibit geometric isomerism? a) CH2=CH-CH3 b) CCl2=CBr2 c) CH3-CH=CH-CH3 d) CHCl=CHCl e) (CH3)2C=CH-CH3 (both c and d) Question 13 Compound A has the formula C4H6. The following scheme show what happens when compound A reacts with various substances. Give structures for compounds A-D. A + excess H2 A + Br2 A + KMnO4 hot, conc B C4H8 C (has two chiral carbons; mark chiral carbons with *) D C4H6O3 A B C D