Chapter 9 Stoichiometry Chapter Review Answers 1. 2. Mole Ratios a. Mole ratios are conversion factors that relate the number of moles of one chemical to another chemical involved in a chemical reaction. b. They are formed from the coefficients found in a balanced chemical equation. Mole Ratios as conversion factors a. b. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 2 ๐๐๐ ๐ถ๐ 1 ๐๐๐ ๐2 2 ๐๐๐ ๐ถ๐๐ , , , 2 ๐๐๐ ๐ถ๐ , 1 ๐๐๐ ๐2 , 2 ๐๐๐ ๐ถ๐๐ . ๐ ๐๐๐๐๐๐๐ ๐กโ๐ ๐๐๐ก๐๐๐ ๐๐๐ ๐๐ ๐๐๐๐ข๐๐๐ ๐๐ ๐ค๐๐๐โผ 1 ๐๐๐ ๐2 2 ๐๐๐ ๐ถ๐ 2 ๐๐๐ ๐ถ๐ 2 ๐๐๐ ๐ถ๐๐ 2 ๐๐๐ ๐ถ๐๐ 1 ๐๐๐ ๐2 1 ๐๐๐ ๐๐ 2 ๐๐๐ ๐ป๐น 1 ๐๐๐ ๐๐๐น2 1 ๐๐๐ ๐๐ 1 ๐๐๐ ๐ป2 1 ๐๐๐ ๐๐ , , , , , , 2 ๐๐๐ ๐ป๐น , 1 ๐๐๐ ๐๐๐น2 2 ๐๐๐ ๐ป๐น 1 ๐๐๐ ๐ป2 1 ๐๐๐ ๐๐๐น2 , , , 2 ๐๐๐ ๐ป๐น 1 ๐๐๐ ๐๐ 1 ๐๐๐ ๐๐ 1 ๐๐๐ ๐๐๐น2 1 ๐๐๐ ๐๐ 1 ๐๐๐ ๐ป2 1 ๐๐๐ ๐๐๐น2 2 ๐๐๐ ๐ป๐น 1 ๐๐๐ ๐ป2 2 ๐๐๐ ๐ป๐น 1 ๐๐๐ ๐ป2 105.99 ๐ ๐๐2 ๐ถ๐3 1 ๐๐๐ ๐๐2 ๐ถ๐3 74.10 ๐ ๐ถ๐(๐๐ป)2 1 ๐๐๐ ๐ถ๐(๐๐ป)2 40.00 ๐ ๐๐๐๐ป 1 ๐๐๐ ๐๐๐๐ป 100.09 ๐ ๐ถ๐๐ถ๐3 1 ๐๐๐ ๐ถ๐๐ถ๐3 1 ๐๐๐ ๐๐2 ๐ถ๐3 , 105.99 ๐ ๐๐2 ๐ถ๐3 , 1 ๐๐๐ ๐ถ๐(๐๐ป)2 , 74.10 ๐ ๐ถ๐(๐๐ป)2 , 1 ๐๐๐ ๐๐๐๐ป , 40.00 ๐ ๐๐๐๐ป , 1 ๐๐๐ ๐ถ๐๐ถ๐3 , 100.09 ๐ ๐ถ๐๐ถ๐3 , 1 ๐๐๐ ๐ป2 1 ๐๐๐ ๐๐๐น2 . Molar Mass a. Definition: the mass of one mole of a substance b. Molar mass is used as a conversion factor in stoiciometric calculations to convert mass of a substance to moles of the substance or convert moles of a substance to mass of the substance. Hydrogen + Oxygen ๏ฎ Water a. 5.0 mol H2 b. 2.5 mol O2 Ethane combustion reaction a. 15.8 mol O2 b. 9.00 mol CO2 & 13.5 mol H2O 575 g Na & 886 g Cl2 Iron production reaction a. 75.1 mol CO b. 50.1 mol Fe & 75.1 mol CO2 87,390 g CO or 8.739 × 104 g CO & 12,610 g H2 or 1.261 × 104 g H2 Lightning reaction of N2 & O2 a. 1,10ฬ 0 g NO2 or 1.10 × 103 g NO2 b. 720. g NO or 7.20 × 102 g NO CO2 removal in spacecraft a. 42.04 mol NaOH b. 21.02 mol Na2CO3 & 21.02 mol H2O Double replacement AgNO3 & NaBr a. 463 g NaBr b. 845 g AgBr Soda-acid fire extinguisher a. 3.058 mol NaHCO3 b. 3.058 mol CO2, 1.529 mol Na2SO4, 3.058 mol H2O Sulfuric acid-sodium hydroxide neutralization reaction a. H2SO4 + 2 NaOH ๏ฎ Na2SO4 + 2 H2O b. 37 g H2SO4 c. 53 g Na2SO4 & 14 g H2O Copper & silver nitrate reaction a. 0.0104 mol Cu(NO3)2 b. 0.0104 mol Cu & 0.0209 mol AgNO3 Aspirin production a. 13.5 kg C9H8O4 b. 7.66 kg C4H6O3 c. 4.29 L HC2H3O2 Ideal stoichiometry calculations do not account for factors that can affect the relative amounts of product chemicals formed in reactions. Ideal stoichiometric calculations are based on the amounts of reactants and products under ideal conditions. Real stoichiometric calculations account for actual conditions under which the reaction occurs. The limiting reactant is the chemical in the reaction in least abundance for the reaction; it will be the chemical reactant that runs out first in the reaction. The limiting reactant limits the amount of chemical product(s) that can be formed. The excess reactant(s) will not be used up completely in the reaction; they will be leftover. . 19. Yields a. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. The theoretical yield is the maximum amount of product that can be produced from a given amount of a reactant. The actual is the measured amount of the chemical product(s) obtained in the laboratory. b. Actual yield is equal to or (& most usually) less than the theoretical yield. % yield is the ratio comparison of the actual yield to the theoretical yield multiplied by 100 to make the ratio a percent. Reactions often do not go to completion and some reactants are leftover. Impurities in the reactants throw off the theoretical yield. Competing side reactions might occur causing different chemical products to be formed. Some of the product is lost during the collection process, or when being separated and purified. Limiting reactants: a. HCl is the limiting reactant b. Zn is the limiting reactant c. Fe(OH)3 is the limiting reactant Excess reactants: a. 0.5 mol NaOH b. 1.0 mol HCl c. 0.5 mol H2SO4 Theoretical yields: a. 2.0 mol NaCl & 2.0 mol H2O b. 2.5 mol ZnCl2 & 2.5 mol H2 c. 2.0 mol Fe2(SO4)3 & 12 mol H2O Cu & AgNO3 single replacement reaction: Cu + 2 AgNO3 ๏ฎ 2 Ag + Cu(NO3)2 a. Cu is the limiting reactant b. 0.50 mol AgNO3 c. 2.50 mol Cu(NO3)2 & 5.00 mol Ag d. 469 g Cu(NO3)2 & 539 g Ag Sulfuric acid & aluminum hydroxide neutralization reaction: 3 H 2SO4 + 2 Al(OH)3 ๏ฎ Al2(SO4)3 + 6 H2O a. H2SO4 is the limiting reactant b. 9.05 g excess Al(OH)3 c. 34.9 g Al2(SO4)3 & 11.0 g H2O Rocket fuel reaction a. N2O4 is the limiting reactant and will run out 1st. b. 2,350. kg H2O Using the % yield equation: a. 75.0% b. 0.90 g c. 95.0% d. 1.66 g 93.2 g PCl5 10,200 g HNO3 or 1.02 × 104 g HNO3 72.46% 10.2 g NaHCO3 (baking powder) 7.10 × 102 g CH4 or 710. g CH4 1.75 × 103 g CH4 or 1,750 g CH4 547 L water vapor 3.23 g Au The chemical equation shows the theoretical yield of product(s) expected under ideal conditions. Since it is rare for a reaction to meet ideal conditions, the actual yield is usually less than the theoretical yield predicted by the equation. To ensure that all the magnesium is converted to MgO, pure oxygen should be used instead of air. In air, there are other chemicals, most notably N2, which could react with the Mg producing magnesium nitride, Mg3N2. Also, the pure O2 should be in excess. A % yield greater than 100% is not possible because the actual yield can never be greater than the theoretical yield. A calculated % yield greater than 100% can only happen due to error. For example, the product might not be completely dry, there could be contaminant chemicals from the reaction, and there might have been side reactions that occurred producing more massive products than expected. Smoldering campfire is not getting enough oxygen to produce the products of complete combustion. Blowing on the smoldering fire might increase the amount of oxygen, allowing the reaction to continue to completion.