Unit Five: Stoichiometry Name Unit Five MC Practice Dec. 5, 2016 In the space provided, write the letter of the term or phrase that best completes each sentence or best answers each question. 1. Stoichiometry is the branch of chemistry that deals with elements in compounds and with reactants and products in chemical reactions, focusing on a. bonding. b. energy transfers. c. mass relationships. d. physical characteristics. 2. The number of significant figures in an answer to a stoichiometry problem is determined only by a. the number of significant figures in the mole ratio used to solve the problem. b. the number of decimal places in the molar masses of substances in the chemical equation. c. the number of significant figures of any measured quantities in the problem. d. the number of significant figures in the molar masses of substances in the chemical equation. 3. The chemical equation P4O10 + 6H2O 4H3PO4 can be interpreted correctly as a. 1 molecule of P4O10 + 6 molecules of H2O form 4 molecules of H3PO4. b. 1 mol of P4O10 + 6 mol of H2O reacts to form 4 mol of H3PO4. c. 1 g of P4O10 + 6 g of H2O produces 4 g of H3PO4. d. Both (a) and (b) 4. In stoichiometry, molar mass is used to a. determine the mole ratio. b. balance a chemical equation. c. convert the amount in moles of one substance to an amount in moles of another substance. d. relate the mass of a substance to the amount in moles of that substance. 5. In the chemical reaction described by the equation 4Fe(s) + 3O2(g) 2Fe2O3(s), the mole ratio of iron(iii) oxide to iron is a. 1:1. b. 1:2. c. 2:3. d. 4:1. 6. What is the unit for the following expression: mass a. mol 2 /g b. g/mol 2 c. mol d. g 1
7. In the chemical equation wa + xb yc + zd, if you know the number of moles of A that react, you can determine a. the number of moles of each reactant and product. b. the number of moles of B only. c. the total number of moles of C and D only. d. the total number of moles of A and B only. 8. Complete the following solution plan: a. mol of given. b. mol of unknown. c. mol given mol unknown. d. (mol given) 2. 9. How many mole ratios can be correctly obtained from the chemical equation 2Al2O3(l) 4Al(s) + 3O2(g)? a. 3 b. 4 c. 6 d. 8 10. In a stoichiometric calculation to determine the mass of one substance that will react with a given amount, in moles, of a second substance, you need to know a. only the mole ratio of the unknown substance to the given substance. b. only the molar mass of the given substance. c. both the mole ratio of the unknown substance to the given substance and the molar mass of the unknown substance. d. the molar masses of all products and reactants. 11. If, in the reaction A + B C + D, the quantity of B is insufficient to react with all of A, a. A is the limiting reactant. b. B is the limiting reactant. c. Both (a) and (b) d. Neither (a) nor (b) For items 12-14, use the following equation, which represents a reaction used commercially to produce elemental arsenic by heating arsenic(iii) oxide with carbon. 2As2O3 + 3C 3CO2 + 4As 12. If 6.0 mol of each reactant are available for the above reaction, the mixture remaining after the reaction should contain a. 4.0 mol As2O3. b. 3.0 mol C. c. 2.0 mol As2O3. d. no reactants. 13. If 6.0 mol of each reactant are available for the above reaction, the mixture remaining after the reaction should contain a. 4.0 mol As. b. 4.0 mol CO2. c. 6.0 mol CO2. d. equal quantities of the products. 2
14. If 8.0 mol As2O3 reacts with excess carbon, the theoretical yield of the above reaction is a. 32 mol As. b. 16 mol As. c. 8 mol As. d. 4 mol As. 15. The measured amount of product obtained from a chemical reaction is the a. percentage yield. b. theoretical yield. c. actual yield. d. mole ratio. 16. The efficiency of a chemical reaction is best expressed by the a. actual yield. b. theoretical yield. c. percentage yield. d. actual yield + theoretical yield. 17. Actual yield is affected by a. side reactions that compete with the main reactions. b. reverse reactions that cause products to re-form reactants. c. amounts of reactants. d.all of the above 18. If the percentage yield of I2 is 80% for the following equation, I2O5 + 5CO I2 + 5CO2, then a. 20% of the reactants remain. b. the percentage yield of CO2 is 80%. c. Both (a) and (b) d. Neither (a) nor (b) 19. A balanced chemical equation allows one to determine the a. mole ratio of any two substances in the reaction. b. energy released in the reaction. c. electron configuration of all elements in the reaction. d. mechanism involved in the reaction. 20. The actual yield of a chemical reaction is generally a. less than the theoretical yield. b. greater than the theoretical yield. c. equal to the percentage yield. d. greater than the percentage yield. 21. To determine the limiting reactant in a chemical reaction involving known masses of the two reactants, which of the following would be most useful? a. determining the masses of 100 mol of each reactant b. determining the molar masses of the products c. calculating bond energies d. calculating the mass of a single product formed from each reactant 3
22. Which expression can be used to solve a mass-to-mole conversion for the equation 2HCL H2 + Cl2? a. b. c. d. 23. In the equation 2Al2O3 4Al + 3O2, what is the mole ratio of aluminum to oxygen? a. 10:6 b. 3:4 c. 2:3 d. 4:3 24. The participation of reactants in a chemical reaction is restricted by the a. limiting reactant. b. limiting product. c. excess reactant. d. excess product. 25. Which of the following expressions is not a legitimate conversion factor? a. b. c. d. 26. For the equation P4 (s) + 5O2 (g) P4O10 (s), if 3 mol of phosphorus react with 10 mol of oxygen, the theoretical yield of phosphorus(v) oxide will be a. 1 mol. b. 2 mol. c. 3 mol. d. 10 mol. 27. If the percentage yield for a chemical reaction is 80.0%, the a. actual yield is 80.0 g for every theoretical yield of 100. g. b. theoretical yield is 80.0 g for every actual yield of 100. g. c. actual yield is 80 times as much as the theoretical yield. 28. In the formation of silicon carbide represented by the chemical equation SiO 2 (s) + 3C(s) SiC(s) + 2CO(g), 8 mol of each reactant are available for the reaction. What substance is the excess reactant? a. SiO2(s) b. C(s) c. SiC(s) d. CO(g) 4
29. In the reaction represented by the equation CH4(g) + 2O2(g) CO 2 (g) + 2H 2 O(g), a mass of 125 g CH 4 is reacted with excess oxygen. The expression is used to calculate the a. mass of oxygen reacted. b. mass of carbon dioxide produced. c. mass of water produced. d. None of the above 30..For the reaction represented by the equation SO3 + H2O H2SO4, what is the percentage yield if 500. g of sulfur trioxide react with excess water to produce 575 g of sulfuric acid? a.82.7% b. 88.3% c.91.2% d. 93.9% 31. If the percentage yield for the reaction represented by the following equation is calculated to be 75.3%, what mass of Al is expected from the reaction of 52.5 g of Al2O3? 2Al2O3(l) 4Al(s) + 3O 2 (g) a. 20.9 g Al b. 42.5 g Al c. 64.0 g Al d. 96.0 g Al 32. Ozone, O3, is produced in automobile exhaust by the reaction represented by the equation NO2(g) + O 2 (g) NO(g) + O 3 (g) What mass of ozone is predicted to form from the reaction of 2.0 g NO2 in a car s exhaust and excess oxygen? a. 1.1 g O3 b. 1.8 g O3 c. 2.1 g O3 d. 4.2 g O3 33. A 0.15 M solution of HCl reacts with an excess of calcium carbonate, CaCl3. A volume of 25.0 ml of HCl is used. To determine the number of moles of CaCl2 produced, you need to know a. the amount of the other product produced. b. the molar mass of HCl. c. the molar mass of CaCl2. d. the balanced chemical equation for the reaction. 5
34. A 0.100 M solution of copper(ii) nitrate reacts with an excess of iron. What do you need to know to calculate the number of moles of iron(ii) nitrate produced? a. the amount of the other product produced b. the volume of solution c. the molar mass of copper(ii) nitrate d. the molar mass of iron(ii) nitrate 35. How many moles of BaCl2 are formed in the reaction with 393 ml of 0.171 M Ba(OH)2 with aqueous HCl? A) 1.15 B) 0.0672 C) 0.0336 D) 2.30 E) 0.134 36. What mass (g) of AgBr is formed when 35.5 ml of 0.184 M AgNO3 is treated with an excess of aqueous hydrobromic acid? A) 53.6 B) 1.44 C) 188 D) 34.5 E) 1.23 37. What is the concentration of nitrate ions in a 0.15 mol/l solution of Fe(NO3)3? a. 0.45 mol/l b. 0.30 mol/l c. 0.15 mol/l d. There is not enough information to answer the question. 38. What is the concentration of a solution of aluminum sulfate (Al2(SO4)3) if the concentration of sulfate ions is 0.60 mol/l/? a. 1.2 mol/l b. 0.60 mol/l c. 0.40 mol/l d. 0.20 mol/l 39. Aspirin is produced by the reaction of salicylic acid (M = 138.1 g/mol) and acetic anhydride (M = 102.1 g/mol). C7H6O3(s) + C4H6O3(l) C9H8O4(s) + C2H4O2(l) If you mix 5.00 grams of each reactant, how many grams of aspirin (M = 180.2 g/mol) can theoretically by obtained? a. 2.83 g b. 3.83 g c. 6.52 g d. 8.82 g e. 10.0 g 40. The reaction of 10.0 g H2(g) with 10.0 g O2(g) yields 8.43 g H2O(g). What is the percent yield of this reaction? a. 9.43% b. 27.3% c. 42.2% d. 66.8% e. 74.9% 6