CHEMISTRY 101 Hour Exam II October 31, 2006 Adams/Le Name KEY Signature T.A./Section Research tells us fourteen out of any ten individuals like chocolate. Happy Halloween! This exam contains 17 questions on 6 numbered pages. Check now to make sure you have a complete exam. You have one hour and fifteen minutes to complete the exam. Determine the best answer to the first 15 questions and enter these on the special answer sheet. Also, circle your responses in this exam booklet. Show all of your work and provide complete answers to questions 16 and 17. 1-15 (30 pts.) 16 (1 pts.) 17 (16 pts.) Total (60 pts) Useful Information: 1.000 L = 1000.0 ml Always assume ideal behavior for gases (unless explicitly told otherwise). PV = nrt R = 0.08206 L atm/mol K K = C + 273 N A = 6.022 x 10 23 Solubility Rules: 1. Most nitrate salts are soluble. 2. Most salts of sodium, potassium, and ammonium cations are soluble. 3. Most chloride salts are soluble. Exceptions: silver(i), lead(ii), and mercury(i) chloride.. Most sulfate salts are soluble. Exceptions: calcium, barium, and lead (II) sulfate. 5. Most hydroxide salts can be considered insoluble. Soluble ones: sodium, potassium, and calcium hydroxide. 6. Consider sulfide, carbonate, and phosphate salts to be insoluble. Soluble ones: sodium and potassium.
Hour Exam II Page No. 1 1. Balance the following equation in standard form and determine the sum of the coefficients. Na S O (aq) + I (aq) 2 2 3 2 2 6 Na S O (aq) + NaI(aq) a) b) 5 c) 6 d) 8 e) 9 2. You have equal concentrations of different solutes in equal volumes of solution. Which of these solutions contains the least mass of solute? a) NH Cl b) CaCl 2 c) MgCl 2 d) SrCl 2 e) All the same. ---------------------------------------------------------------------------------------------------------------- Use the following unbalanced equation to answer questions 3 and. MnO (s) + Al(s) Mn(s) + Al O (s) 2 2 3 3. If 5.00 moles of Mn(s) were produced, how many moles of Al(s) were required? a) 3.33 mol b) 3.75 mol c) 5.00 mol d) 6.67 mol e) none of these. If 2.00 moles of MnO 2 and 2.00 moles of Al are reacted, how many moles of Al 2 O 3 would be produced? a) 1.00 mol b) 1.33 mol c) 2.00 mol d) 3.00 mol e).00 mol ---------------------------------------------------------------------------------------------------------------- 5. Consider the reaction below: Fe(s) + 3O (g) 2Fe O (s) 2 2 3 When 50.0 g Fe and 85.0 g of O 2 are reacted to produce Fe 2 O 3, is mass conserved in the reaction? Choose the best answer. a) No. The different coefficients from reactants to product cause some mass to be lost in the reaction. b) No. We started with 135 g of reactants and only produced 71.5 g of product. c) Yes. The subscripts that appear on the reactant side are also found on the product side, especially when mole ratios are taken into account. d) Yes. There are equal masses before and after the reaction, but the mass of leftover reactant must be taken into account. e) This cannot be determined because only comparisons can be made in moles when analyzing balanced chemical reactions, not grams.
Hour Exam II Page No. 2 6. A 500.0-g sample of potassium phosphate is dissolved in enough water to make 1.50 L of solution. What is the molarity of the solution? a) 1.57 M b) 1.92 M c) 3.53 M d) 333 M e) none of these 7. Which of the following is the correct net ionic equation for the reaction between barium hydroxide and sulfuric acid? a) b) Ba (aq) + SO (aq) BaSO (s) 2+ 2-2+ - + 2-2 Ba (aq) + 2OH (aq) + 2H (aq) + SO (aq) 2H O(l) + BaSO (s) - + c) 2OH (aq) + 2H (aq) 2H2O(l) d) Ba(OH) 2(aq) + H2SO (aq) 2 2H O(l) + BaSO (s) e) There is no net ionic equation for this reaction. ---------------------------------------------------------------------------------------------------------------- Consider the following four solutions to answer questions 8 10. 8. Which of the solutions above contain the greatest number of ions? a) Solution # b) Solution #3 c) Solution #2 d) Solution #1 e) At least two of the above solutions contain the greatest number of ions. 9. You pour Solution #1 and Solution # together in a large, empty beaker. What is the concentration of the new HCl mixture? a) 3.00 M b) 3.25 M c) 3.0 M d).25 M e) 6.50 M 10. How much water would have to be added to Solution #3 to have the same concentration of solute as Solution #2? a) 2.0 L b) 2.3 L c) 3.0 L d) 5.0 L e) 5.3 L
Hour Exam II Page No. 3 11. For the unbalanced reaction: Cr(s) + O 2(g) Cr2O 3(s), How many grams of chromium(iii) oxide can be produced from 15.0 g of solid chromium and excess oxygen gas? a) 3.8 g b) 7.50 g c) 87.7 g d) 0.1 g e) 21.9 g 12. Which of the following statements is false for the reaction of hydrogen gas with oxygen gas to produce water? (a, b, and c represent coefficients) a H (g) + b O (g) 2 2 2 c H O(g) a) The ratio of a / c must always equal one. b) The sum of a + b + c equals 5 when balanced in standard form. c) Coefficient b can equal ½ because coefficients can be fractions. d) The number of atoms on the reactant side must equal the number of atoms on the product side. e) Subscripts can also be used to balance this equation, just as they can be used to balance the charges in an ionic compound. 13. Consider the equation: 3A + B 2C. The molar mass of A is 100.0 g/mol. Which of the following statements must be true when equal masses of A and B are reacted? a) If the molar mass of B is greater than the molar mass of A, then B must determine how much C is produced. b) If the molar mass of B is less than the molar mass of A, then B must determine how much C is produced. c) If the molar mass of B is the same as the molar mass of A, then A and B react in a perfect stoichiometric ratio and both determine how much C is produced. d) If the molar mass of B is less than the molar mass of A, then A must determine how much C is produced. e) If the molar mass of B is greater than the molar mass of A, then A must determine how much C is produced. 1. An air bag is deployed by utilizing the following balanced reaction: 2NaN (s) 2Na(s) + 3N (g) 3 2 What mass of NaN 3 must be used to inflate an air bag to 85.0 L at 1.00 atm and 25 C? a) 3.8 g b) 27.6 g c) 151 g d) 226 g e) 339 g
Hour Exam II Page No. 15. For the reaction of nitrogen gas with oxygen gas to produce nitrogen monoxide gas, which of the following microscopic reactions correctly represents this chemical reaction and produces the most product? a) b) c) d) e)
Hour Exam II Page No. 5 16. a. Using different shapes to distinguish between different elements, draw a balanced equation for the following reaction on the microscopic level. In addition, fill in the box below to specify what element each shape represents. NH (g) + O (g) N (g) + H O(g) 3 2 2 2 N = points H = O = b. If you react 10.0 g of ammonia with 12.0 g of oxygen gas, how many moles of nitrogen gas and how many moles of water are produced? Show all of your work in an organized manner in the space provided. 6 points Student work will vary here. They need to show the following: mass of ammonia and oxygen gas to moles determine the limiting reactant as oxygen gas show that 0.250 mol N 2 is produced show that 0.750 mol H 2 O is produced c. What is the total volume present (in L) after the reaction is complete assuming the reaction takes place at 0. C and 1.00 atm? Show all of your work in an organized manner in the space provided. points Student work will vary here. They need to show the following: how many moles of NH 3 is used up in the reaction (if they didn t show it above) how many moles of NH 3 are leftover o 0.587 mol NH 3 to start 0.500 mol NH 3 used = 0.087 mol NH 3 leftover use the ideal gas law to solve for the total volume PV = nrt o nrt (0.250mol + 0.750mol+ 0.087mol)(0.08206)(273) V = = P 1.00 V = 2. L
Hour Exam II Page No. 6 17. Consider the reaction: 50.0 ml of 2.50 M potassium sulfate is mixed with 100.0 ml of 1.00 M lead(ii) nitrate. 3 points a. Write the balanced molecular, complete ionic, and net ionic equations below. Include all phases in your reactions. MOLECULAR: COMPLETE IONIC: NET IONIC: K SO (aq) + Pb(NO ) (aq) 2KNO (aq) + PbSO (s) 2 3 2 3 + 2-2+ - + - 2K (aq) + SO (aq) +Pb (aq) + 2NO (aq) 2K (aq) + 2NO (aq) +PbSO (s) 3 3 2-2+ SO (aq) + Pb (aq) PbSO (s) b. What mass of solid is produced? Show all of your work in an organized manner in the space provided. points Student work will vary here. They need to show the following: moles of K 2 SO or SO 2- = 0.125 mol moles of Pb(NO 3 ) 2 or Pb 2+ = 0.100 mol determine the limiting reactant as Pb(NO 3 ) 2 or Pb 2+ show that 0.100 mol PbSO is produced show that 30.3 g PbSO is produced (molar mass of PbSO is 303.27 g/mol) 9 points c. What are the concentrations of ions left in solution after the reaction is complete? Place your final answers in the box below and show all of your work in an organized manner. + K = 1.67 M 2- SO = 0.167 M 2+ Pb = 0.00 M - NO 3 = 1.33 M + 2 mol K + + 0.250 mol 0.125 mol K2SO = 0.250 mol K [K ] = 1 mol K SO 0.150 L 2 2 mol NO 0.200 mol 0.100 mol Pb(NO ) 0.200 mol NO [NO ] = 1 mol Pb(NO ) 0.150 L - 3 - - 3 2 = 3 3 3 2 2-2- 2-0.125 mol SO to start - 0.100 mol SO used up = 0.025 mol SO leftover 2-0.025 mol [SO ] = 0.150 L