CHEM 102 General Chemistry I Spring 2015 Exam 3 -­‐ Version A Questions and Answers,100% CORRECT

Instructions: CHEM 102 General Chemistry I Spring 2015 Exam 3 -­‐ Version A Questions and Answers 1. Do NOT open this exam until you are told to do so. Opening the exam before the start of the exam is considered an act of Academic Dishonesty. 2. All answers must be bubbled into the scantron answer sheet. 3. No credit will be given for answers written on this exam. 4. You must use a #2 pencil to bubble in the answers on your scantron. 5. This is a multiple choice exam consisting of 31 questions (7 pages). Each question is worth 6.67 points. There are a total of 206.77 points on this exam. 200 points is full credit. 6. Attached to the back of this exam you will find 3 blank pages and a periodic table. You may remove these from the exam at your convenience. 7. On the FRONT of your scantron. • Write your last name, followed by your first name. • Write your exam version (A or B) 8. On the BACK of your scantron: • Write and bubble in BOTH your last and first name. Make sure to bubble in your names as follows: Last Name (SPACE) First Name NOTE: You must Bubble in the space on your scantron! Multiple Choice Questions: (6.67 pts each) For questions 1 and 2 consider the ionic solid calcium phosphate. 1) The molar mass of calcium phosphate is . a. 135.05 g/mol b. 175.13 g/mol c. 215.21 g/mol d. 310.18 g/mol e. 365.07 g/mol 2) How many moles are there in 8.0 g of calcium phosphate? a. 0.022 moles (full credit if you chose e above) b. 0.026 moles (full credit if you chose d above) c. 0.037 moles (full credit if you chose c above) d. 0.046 moles (full credit if you chose b above) e. 0.059 moles (full credit if you chose a above) 3) How many total ions are there in 44 moles of Na3PO4? a. 2.65 x 1025 ions (3.33 pts partial credit if you forgot to go from molecules to ions) b. 7.95 x 1025 ions c. 1.06 x 1026 ions d. 2.12 x 1026 ions 4) A small glass of water contains 75.96 grams of water. How many moles of hydrogen atoms are in this glass of water? a. 4.22 b. 8.44 c. 5.08 x 1024 d. 2.54 x 1024 5) A solution is known to contain 28% phosphoric acid by mass. This means that: a. The density of this solution is 2.8 g/mL b. 1 mL of this solution contains 28 g of phosphoric acid c. 100 g of this solution contains 28 g of phosphoric acid d. 1 L of this solution has a mass of 28 g e. 1 L of this solution contains 28 mL of phosphoric acid 6) What is the percent by mass of carbon in dimethylsulfoxide (C2H6SO) ? a. 15.4 % b. 20.0 % c. 30.7 % d. 44.3 % 7) The net ionic equation for the reaction of copper(III) nitrate with ammonium phosphate is: a. Cu3+(aq) + 3NH4+(aq) + PO43-­‐(aq)  3NH4+(aq) + CuPO4(s) b. Cu3+(aq) + PO43-­‐(aq)  CuPO4(s) c. Cu3+(aq) + 3NO3-­‐(aq) + 3NH4+(aq) + PO43-­‐(aq)  3NO3-­‐(aq) + 3NH4+(aq) + CuPO4(s) d. Cu(NO3)3(aq) + (NH4)3PO4(aq)  3NH4NO3-­‐(aq) + CuPO4(s) For questions 8 and 9 consider the chemical reaction that occurs when hydrogen sulfide gas reacts with oxygen gas to form water and gaseous sulfur dioxide. 8) Write the balanced chemical equation for this reaction. a. 2H2S(g) + 3O2(g)  2H2O(l) + 2SO2(g) b. H2S(g) + O2(g)  H2O(l) + SO2(g) c. 4HS(g) + 5O2(g)  2H2O(l) + 4SO2(g) (3.33 pts partial credit for using HS) d. HS(g) + O2(g)  H2O(l) + SO2(g) 9) This reaction is an example of a reaction? a. decomposition reaction b. double displacement reaction c. synthesis reaction d. combustion reaction For questions 10 and 11 consider the combustion of ammonia in the presence of oxygen to yield nitrogen dioxide and water: 4NH3(g) + 7O2(g)  4NO2(g) + 6H2O(g) 10) If the reaction runs to 100% completion and 28.8 g of ammonia are completely combusted, how many grams of oxygen are consumed? a. 94.8 b. 54.1 c. 50.4 d. 30.9 (3.33 pts partial credit if you inverted the mole ratio) e. 16.5 11) If 4.50 grams of ammonia react with 8.80 grams of oxygen what is the maximum amount of nitrogen dioxide that can be made? a. 12.2 g NO2 b. 7.23 g NO2 (You must remember to do the limiting reagent calculation) c. 5.03 g NO2 d. 4.50 g NO2 12) Consider the chemical reaction A + B  C . Imagine that you go into the lab and react 3.00 g of A with 3.00 g of B. If you produce 4.05 g of product and the yield of the reaction is 76%, then the theoretical yield for the reaction is and the actual yield is . a. 6.00 g and 4.05 g b. 5.34 g and 4.05 g c. 4.05 g and 3.08 g (3.33 pts partial credit if you used 4.05 grams as the theoretical yield) d. 4.05 g and 5.34g 13) Aspirin (C9H8O4, Mw = 180.154 g/mol) is prepared by the acetylation of salicylic acid (C7H6O3, Mw = 138.118 g/mol) according to the following equation: C7H6O3 + (CH3CO)2O  C9H8O4 + CH3COOH If the yield of this reaction is 83%, what mass of salicylic acid would be needed to prepare 1 kg of aspirin? a. 0.77 kg b. 0.92 kg (Remember to find the Theoretical yield first  1.204 kg) c. 1.2 kg d. 1.3 kg 14) An unknown compound is known to contain C, H and Cl in the percentage ratio shown in the table below. How many carbon atoms are there in the empirical formula for this compound? a. 3 b. 4 c. 5 d. 6 e. 7 15) What is the molecular formula of a compound if the molar mass of the compound is found to be 186.5 gram and the empirical formula is C2H7? a. C2H7 b. C6H21 c. C12H14 d. C12H42 16) You are hired by a chemical company to determine the empirical formula of an unknown alcohol that contains only three elements, carbon, hydrogen, and oxygen. You go into the lab and combust a 50.00 gram sample of the alcohol. The reaction produces 95.50 grams of CO2 and 58.70 grams of H2O. What is the empirical formula of the alcohol? a. CHO b. CH3O c. C2H6O d. C2H8O2 17) Pure samples of which of the following compounds will exhibit hydrogen bonding? I CH3OH II CH3NH2 III CH3CN a. I only (3.33 pts partial credit if you chose only the alcohol) b. I and II only c. II and III only d. I, II and III 18) Arrange the following in order of increasing boiling point: RbCl, CH3Cl, CH3OH, CH4. a. CH3OH < CH3Cl < RbCl < CH4 b. CH4 < CH3Cl < RbCl < CH3OH (3.33 pts partial credit if you forgot that ionic bonds are stronger than all IMFs and so RbCl will have the highest BP) c. RbCl < CH3Cl < CH3OH < CH4 d. CH4 < CH3Cl < CH3OH < RbCl 19) Examine the phase diagram for an unknown substance X shown below. How many of the following statements are correct based on this phase diagram? I. The triple point for X is at a higher temperature than the normal melting point. II. X changes from a solid to a liquid as one follows the line from C to D. III. X undergoes sublimation as one follows the line from C to D. a. Only II is correct b. Only III is correct c. I and II are correct d. I and III are correct e. II and III are correct. 20) What is the concentration of nitrate ion in a solution that contains 0.900 M aluminum nitrate? a. 2.70 M (Al(NO3)3 so there are 3 moles of nitrate for every 1 mole of (Al(NO3)3)) b. 1.80 M c. 0.900 M d. 0.450 M 21) Imagine you leave a 750 mL solution of 0.5 M sodium chloride uncovered on the windowsill and 150 mL of the solvent evaporates. What is the concentration of sodium chloride in the solution after the evaporation? a. 0.10 M b. 0.38 M c. 0.63 M d. 0.75 M 22) If you mix 1 mole of aqueous Fe(NO3)3 with 2 moles of aqueous Na2CO3, what species will be present in the test tube after the reaction? a. solid iron (III) carbonate, sodium ions, nitrate ions, carbonate ions, water b. solid iron (III) carbonate, sodium ions, nitrate ions, iron ions, water c. solid iron (III) carbonate, sodium ions, nitrate ions, water (3.33 pts partial credit if you forgot to balance the reaction and consider the excess reagent left over) d. solid iron (III) carbonate, sodium nitrate molecules, water For questions 23 -­‐ 27 consider a fixed number of moles of unknown gas at a constant 31°C. 23) In order to double the pressure in the system the volume will have to a. Increase by a factor of 2 b. Increase by a factor of 1.414 c. Decrease by a factor of 2 (P and volume are inverse functions: P1/P2 = V2/V1) d. Decreasedby a factor of 1.414 24) The reason the pressure changes in the question above is because: a. The gas particles begin to move more quickly. b. The average force of the collisions with the walls of the containter changes c. The frequency of the collisions with the walls of the container changes d. Both the frequency and force of the collisions change 25) If you allow the sample of unknown gas to expand to double its current volume, but the number of moles and temperature remain constant, the average velocity of the gas will: a. increase b. decrease c. stay the same (remember velocity depends on KE and KE depends on T only) d. you need to know the pressure of the system to answer this question. 26) If helium diffuses twice as fast as the unknown gas above, the identity of the unknown gas might be: a. Hydrogen (H2) Remember that the unknown must be heavier than He (it moves more slowly) so it cannot be H2 b. Neon (Ne) c. Methane (CH4) (velocity and mass are inverse functions: ν12/ ν 22 = Mw2/Mw1) d. Argon (Ar) 27) If you raise the temperature in the container to 56°C, by what factor would the average speed of the molecules increase? a. 1.81 b. 1.34 c. 1.08 (3.33 pts partial credit if you forgot to take the square root) d. 1.04 (velocity and temperature are proportional: ν12/ ν 22 = T1/T2) 28) A sample of a gas originally at 25 °C and 1.00 atm pressure in a 2.5 L container is allowed to expand until the pressure is 0.85 atm and the temperature is 15 °C. What is the final volume of the gas after the expansion? a. 3.0 L b. 2.8 L c. 2.6 L d. 2.1 L e. 0.38 L 29) The density of air at STP is 1.285 g/L. Which of the following cannot be used to fill a balloon that will float in air at STP? a. CH4 b. NO (find the Mw of the air = 29 g/mol and then choose the gas that is heavier) c. Ne d. NH3 e. HF 30) Calcium hydride (CaH2, Mw = 42.09 g/mol) is a grey powder that reacts violently with water in an exothermic reaction to produce hydrogen gas and calcium hydroxide. If you want to produce 48 L of hydrogen gas at a pressure of 0.888 atm and a temperature of 32 °C, how much CaH2 must you start with? You may presume that the reaction runs to 100% completion. a. 0.851g b. 35.8 g c. 50.7 g d. 71.7 g (3.33 pts partial credit if you forgot to balance the reaction and so you used a 1:1 mole ratio) 31) The mineral trona has the chemical formula Na2CO3NaHCO32H2O and a molar mass of 226 g/mol. How many mL of 0.125 M HCl are needed to convert all of the carbonate (CO32-­‐) and bicarbonate (HCO3-­‐) in a 0.407 g sample of trona into carbon dioxide and water. a. 43.2 mL b. 28.8 mL (3.33 pts partial credit if you balanced the equation using 2 HCl instead of 3 HCl because you missed the 3 Na ions in the trona) c. 21.6 mL d. 14.4 mL