# Unit 9 Stoichiometry Notes (The Mole Continues)

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1 Unit 9 Stoichiometry Notes (The Mole Continues) is a big word for a process that chemist s use to calculate amounts in reactions. It makes use of the coefficient ratio set up by balanced reaction equations to make connections between the and in a reactions. Stoichiometry calculates the quantities of reactants and products in a chemical reaction. The! Questions that deal with amounts in reactions are examples of reaction stoichiometry. We already have the tools necessary to solve this question. We just need to learn a new way to apply skills such as formulas, formula masses, and converting from mass to, particles to, and volume of gases to. Mole to Mole Conversions you must have. Illustration: Let s use an analogy that we can understand to begin to understand the process. The KEY to any mole conversion is the ratio of coefficients in the reaction equation. Say I want to make a bacon double cheeseburger. Let s get our recipe together. 1 hamburger bun + 2 hamburger patties + 2 slices of cheese + 4 strips of bacon 1 bacon double cheeseburger Based on this recipe: 1) If I have five bacon double cheeseburgers: a. How many hamburger buns did you use? b. How many hamburger patties did you use? c. How many slices of cheese did you use? d. How many strips of bacon did you use? 2) How many bacon double cheeseburgers can you make if you start with: a. 2 buns, 4 patties, 4 slices of cheese, 8 strips of bacon b. 1 dozen buns, 2 dozen patties, 2 dozen slices of cheese, 4 dozen strips of bacon c. 1 mole of buns, 2 mol of patties, 2 mol of cheese slices, 4 mol of bacon strips d. 10 buns, 20 patties, 2 slices of cheese, 40 strips of bacon To think through these questions we were using the ratios set up by the reaction equation (a.k.a. recipe) We understood that to produce one complete bacon double cheeseburger we needed to have each of the above ingredients in a 1 bun to 2 patties to 2 slices of cheese to 4 slices of 1

2 bacon. This ratio is called the coefficient ratio. If we want to make 3 sandwiches then we would just triple all of the coefficients. THIS IS KEY TO DOING STOICHIOMETRY. Let s apply the above logic to a chemical recipe (a.k.a. chemical reaction equation). 1 H 2 SO NaOH 1 Na 2 SO H 2 O If I use 1 mole of H2SO4 How many moles of sodium hydroxide do I need? How many moles of sodium sulfate do I make? Consider: The reaction 2H 2 + O 2 2H 2 O. How many moles of water will be produced Mole to Mass. How many grams of water will be produced if there are 3.5 moles of oxygen? 2

3 Mass to Mass. What mass of barium phosphate can be produced from 14.3 g of potassium phosphate reacting with barium nitrate? What mass of bromine gas can be produced from the complete reaction of potassium bromide and 34.5 g of fluorine gas? 3

4 Mole to Mole Practice Consider the equation: aa bb Moles of A b moles of B = Moles of B a moles of A 1) N2 + 3 H2 2 NH3 How many moles of hydrogen are needed to completely react with two moles of nitrogen? 2) 2 KClO3 2 KCl + 3 O2 How many moles of oxygen are produced by the decomposition of six moles of potassium chlorate? 3) Zn + 2HCl ZnCl2 + H2 How many moles of hydrogen are produced from the reaction of three moles of zinc with an excess of HCl? 4) C3H8 + 5O2 3CO2 + 4H2O How many moles of oxygen are necessary to react completely with four moles of propane (C3H8)? 5) K3PO4 + Al(NO3)3 3 KNO3 + AlPO4 How many moles of potassium nitrate are produced when two moles of potassium phosphate react with two moles of aluminum nitrate? 4

5 Mass to Mole Practice Consider the equation: aa Mass of A 1 mol A b mol B Molar Mass A a mol A bb = moles of B Consider the following balanced equation to answer AgNO3(aq) + MgBr2(aq) 2 AgBr(s) + Mg(NO3)2(aq) 1) Calculate the mass of silver bromide produced from 0.01 moles of silver nitrate. 2) Calculate the number of moles of magnesium nitrate formed from 55.3 grams of silver nitrate. 3) Calculate the number of moles of silver bromide produced from 212 g of magnesium bromide. Consider the following balanced equation to answer 4-5. MnO2(s) + 4 HCl(aq) MnCl2 + 2 H2O(l) + Cl2(g) 4) Calculate the mass of MnO2 required to completely react with 2.5 moles of water. 5) What amount of chlorine gas is produced from 72 grams of HCl? 5

6 Mass to Mass Practice Consider the equation: aa bb Grams A 1 mol A b mol B Molar Mass B = Mass Molar Mass A a mol A 1 mol B B 1) N H 2 2 NH 3 How many grams of hydrogen are necessary to completely react with 50.0 g of nitrogen in the above reaction? 2) 2 KClO 3 2 KCl + O 2 a) How many grams of potassium chloride are produced if 25 grams of potassium chlorate decompose? b) How many grams of oxygen are produced from 25 grams of potassium chlorate? 3) Zn + 2HCl ZnCl 2 + H 2 How many grams of hydrogen gas are produced from the reaction of 221 grams of zinc with an excess of HCl? 4) Iron will react with oxygen to produce Fe 2 O 3. How many grams of Fe 2 O 3 will be produced from 37.5 grams of iron. (Hint: write a balanced equation) 6

7 5) C 3 H 8 + 5O 2 3CO 2 + 4H 2 O a) How many grams of oxygen are necessary to react completely with 33 grams of propane (C 3 H 8 )? b) How many grams of carbon dioxide are produced in the reaction above? c) How many grams of water are produced in the reaction above? 6) K 3 PO 4 + Al(NO 3 ) 3 3 KNO 3 + AlPO 4 How many grams of potassium nitrate are produced from 105 grams of aluminum nitrate? 7) Carbon will react with zinc oxide to produce zinc and carbon dioxide. How many grams of carbon dioxide will be produced if 135 grams of ZnO is completely reacted? (Hint: write a balanced equation) 7

8 STOICHIOMETRY PRACTICE Show ALL work for the following reactions. Be sure to include a complete and balanced reaction. 1) If 95 grams of Iron are needed to react with sulfur, how many grams of sulfur are involved in this reaction? (Iron (III) Product will form) 2) What mass of Sulfurous acid is produced, when 245g of Sulfur Dioxide is reacted with water? 3) If 45g of Sodium Chloride reacts with Silver Nitrate solution, what mass of silver chloride will be produced? 4) When 6.38 x atoms of Chlorine gas reacts with potassium iodide solution, how many grams of potassium chloride are produced? 5) If 84.9g of solid iron reacts with oxygen gas.(iron III Product Forms), how many atoms of oxygen will react? 6) How many grams of hydrogen gas will be produced from the reaction of zinc metal with 85 grams of Hydrochloric Acid? 8

9 7) The Haber process for the production of ammonia gas, NH 3 is represented by reacting nitrogen gas with hydrogen gas under special conditions of pressure and temperature. The complete conversion of 90.0 grams of hydrogen to ammonia would require how many atoms of nitrogen gas? 8) Potassium chlorate decomposes into potassium chloride and oxygen gas. How many grams of oxygen will be produced if 38 grams of potassium chlorate decomposes? 9) Methane (CH 4 ) is produced by reacting hydrogen gas with coke (pure carbon). How many grams of methane gas will be produced if 7.98*10 24 atoms of hydrogen gas are available to react? 10) If 5.0 g of copper metal reacts with a solution of silver nitrate, how many grams of silver metal are recovered? (Copper II Product) 9

10 Molar Volume Notes Avogadro s Law states that ONE MOLE of ANY gas will occupy. STP is standard temperature and pressure. The conditions are. What is the volume of 5.68 moles of butane (C 4 H 8 ) at STP? Calculate the number of molecules of 23.5 L of oxygen gas at STP. What is the volume of 5.68 g of iodine gas at STP? 10

11 Volume Practice 1) Find the mass of sugar (C 6 H 12 O 6 ) required to produce 1.82 L of carbon dioxide gas at STP from the reaction described by the following equation: C 6 H 12 O 6 + 6O 2 6 H 2 O + 6 CO 2 2) Find the mass of benzene gas required to produce 2.66 L of carbon dioxide gas at STP using the balanced equation below. 2 C 6 H O 2 6 H 2 O + 12 CO 2 3) Propane gas (C 3 H 8 ) burns in oxygen according to the equation: C 3 H 8 + 5O 2 3CO 2 + 4H 2 O. What volume of carbon dioxide is produced when 2.8 L of oxygen are consumed? 4) TNT (trinitrotoluene) decomposes explosively into carbon, carbon monoxide, hydrogen, and nitrogen. What volumes of hydrogen AND nitrogen are produced if 5.8 L of CO is produced? (Hint, you should have an answer for hydrogen AND for nitrogen.) 2 C 7 H 5 (NO 2 ) 3 2 C + 12 CO + 5 H N 2 vol H 2 : vol N 2 : 11

12 5) Consider the equation: 2H 2 S + 3 O 2 2 SO H 2 O a. How many molecules of water are produced when 12 moles of oxygen are reacted? b. For the reaction, 8.04x10 24 molecules of H 2 S reacts with oxygen. Determine the mass of sulfur dioxide produced. 6) Consider the reaction: Sb 2 O C 2 Sb + 3 CO a. How many molecules of carbon monoxide are produced when grams of Sb 2 O 3 are reacted? b. For the reaction, 3.01 x molecules of carbon are reacted. Determine the mass of antimony (Sb) produced. c. If the reaction of grams of carbon occurs at STP, how many liters of carbon monoxide gas are produced? 12

13 Mixed Practice 1. In a very violent reaction called a thermite reaction, aluminum metal reacts with iron(iii) oxide to form iron metal and aluminum oxide according to the following equation: Fe 2 O 3 + 2Al 2Fe + Al 2 O 3 a. What mass of Al will react with 150 g of Fe 2 O 3? b. If mol Al 2 O 3 is produced in the reaction, what mass of Fe is produced? c. How many moles of Fe 2 O 3 will react with 99.0 g of Al? 2. Ammonium nitrate decomposes to yield nitrogen gas, water, and oxygen gas in the following reaction: 2NH 4 NO 3 2N 2 + O 2 + 4H 2 O a. How many moles of nitrogen gas are produced when 36.0 g of NH 4 NO 3 reacts? b. If 7.35 mol of H 2 O are produced in this reaction, what mass of NH 4 NO 3 reacted? 3. Lead(II) nitrate reacts with potassium iodide to produce lead(ii) iodide and potassium nitrate. If 1.23 mg of lead nitrate are consumed, what is the mass of the potassium nitrate produced? (Hint: write a balanced equation for the reaction.) 4. In a space shuttle, the CO 2 that the crew exhales is removed from the air by a 13

14 reaction within canisters of lithium hydroxide. On average, each astronaut exhales about 20.0 mol of CO 2 daily. The other product of the reaction is Li 2 CO 3. a. Write a balanced equation for this reaction. b. What mass of water will be produced when this amount reacts with LiOH? c. How many molecules of water will be produced if the five member crew exhales 4400 grams of CO 2? 5. A reaction between hydrazine, N 2 H 4, and dinitrogen tetroxide, N 2 O 4, has been used to launch rockets into space. The reaction produces nitrogen gas and water vapor. a. Write a balanced chemical equation for this reaction. b. How many moles of N 2 will be produced if 20,000 mol of N 2 O 4 are used by a rocket? d. How many grams of H 2 O are made when 450 L of N 2 O 4 are consumed at STP? 14

15 Limiting Reactants Notes In all reactions, there will be one reactant that will limit the yield of the product. The limiting reactant is not always the one present in the smallest quantity the MOLAR RATIO needs to be taken into consideration. What mass of aluminum sulfide can be produced from 9.00 g of aluminum reacting with 8.00 g of sulfur? What is your limiting reactant? What mass of aluminum sulfate can be produced from the reaction of 20.0 g of sulfuric acid with 25.0 g of aluminum hydroxide? o What mass of the excess reactant will remain at the completion of the reaction? What mass of zinc sulfide can be produced from the reaction of g of zinc reacting with g of sulfur? Indicate the limiting reactant. o What mass of the excess reactant will remain at the completion of the reaction? 15

16 Limiting Reactants 1. Sodium chloride can be prepared by reacting sodium metal with chlorine gas. Write and balance the chemical equation for this process. a. How many grams of sodium chloride will be produced when 6.70g of sodium reacts with 3.20g of chlorine gas? b. Which is the limiting reactant? 2. Hydrogen gas can be formed in the laboratory by the reaction of magnesium metal with hydrochloric acid (HCl). Write and balance the reaction for this process. a. How many grams of hydrogen can be produced when 6.00 g of HCl is added to 5.00 g of Mg? b. Which of the reactants is the limiting reagent? 3. Hydrazine, or dinitrogen tetrahydride, is used as rocket fuel. It reacts with oxygen to form nitrogen gas and water. Write and balance the equation for this process. a. How many liters will be formed from 1.0 g of hydrazine reacts with 1.0 g of oxygen? b. Indicate the limiting reactant 16

17 % YIELD OF REACTIONS 1. Calcium carbonate decomposes into calcium oxide and carbon dioxide. Calculate the % yield if 97.5 g of carbon dioxide is recovered from g of calcium carbonate. 2. Zirconium (IV) iodide is decomposed to obtain pure zirconium. What is the % yield for this process if 5.00g of pure zirconium is obtained from the decomposition of 45.0 g of Zirconium (IV) iodide? 3. If 15.0 g of nitrogen reacts with 15.0 g of hydrogen, 10.5 g of ammonia is produced. Calculate the % yield of this reaction. 4. Silicon dioxide and hydrofluoric acid (hydrogen fluoride) react to produce hexafluorosilicic acid (H 2 SiF 6 ) and water. Calculate the % yield if 40.0 g of silicon dioxide reacts with 40.0 g of hydrofluoric acid and 45.8g of hexafluorosilicic acid is produced. 5. What mass of aluminum oxide will form if the reaction of 34.5 g of aluminum and 45.0 L of oxygen gas proceeds at a 78.2% yield? 17

18 Limiting Reactants and Percent Yield 1. Identify the limiting and excess reagents when 25 L of nitrogen reacts with 25 L of hydrogen at STP. How many liters of ammonia gas are formed in this reaction? N 2 + H 2 NH 3 2. If 6.57 g of iron are reacted with an excess of hydrochloric acid, HCl, then hydrogen gas and g of iron(iii) chloride are obtained. Calculate the theoretical yield and percent yield of FeCl 3. Fe + HCl H 2 + FeCl 3 3. A chemist burns 160. g of aluminum in oxygen to produce aluminum oxide. She produces 260. g of aluminum oxide. Write a balanced equation and calculate the theoretical yield and percent yield. 4. You need to produce g of FeCl 3 in the reaction from #2. If the percent yield of the reaction is 85%, how many grams of iron do you need to start with? 18

19 Unit 9 Test Review 1. What is the volume of 67.4 g of hydrogen gas at STP? 2. What is the volume of 56.8 g of chlorine gas at STP. 3. If 95 grams of Iron are needed to react with sulfur, how many grams of sulfur are involved in this reaction? (Iron (III) Product will form) 4. What mass of Sulfurous acid is produced, when 245g of Sulfur Dioxide is reacted with water? 5. If 45g of Sodium Chloride reacts with Silver Nitrate solution, what mass of silver chloride will be produced? 6. When 78.2 L of Chlorine gas reacts with potassium iodide solution, how many grams of potassium chloride are produced? 7. If 84.9g of solid iron reacts with oxygen gas.(iron III product forms), what volume of oxygen will react? 19

20 8. How many grams of hydrogen gas will be produced from the reaction of zinc metal with 85 grams of Hydrochloric Acid? 9. The Haber process for the production of ammonia gas, NH 3 is represented by reacting nitrogen gas with hydrogen gas under special conditions of pressure and temperature. The complete conversion of 90.0 grams of hydrogen to ammonia would require how many liters of nitrogen gas? 10. Potassium chlorate decomposes into potassium chloride and oxygen gas. How many grams of oxygen will be produced if 38 grams of potassium chlorate decomposes? 11. Identify the limiting reactant when 10.7 g of Silver reacts with 8.9 L of chlorine gas at STP? What mass of product can be formed? 12. Identify the limiting reactant when 18.2 g of H 2 O reacts with 14 g K. What mass of KOH is formed? 13. Identify the limiting reactant when 85.2 g of H 2 S at STP is reacted with 18.0g of NaOH. What mass of H 2 O is produced? 20

21 14. When 45.0L of chlorine gas reacts with excess aluminum, 165g of aluminum chloride are produced. What is your % yield? 15. Adipic Acid, H 2 C 6 H 8 O 4, is used to produce nylon. It is made commercially by a controlled reaction between cyclohexane (C 6 H 12 ) and O 2 as presented in the following UNBALANCED reaction. C 6 H 12 + O 2 H 2 C 6 H 8 O 4 + H 2 O Assume that you carry out this reaction starting with 25.0 g of cyclohexane and excess oxygen. The reaction proceeds at a 77.0% yield. How many grams of adipic acid can you produce? 16. Iron ore containing iron (III) oxide is converted into iron by way of reacting it with carbon monoxide to produce iron and carbon dioxide. If you start with 150. g of iron ore in the presence of excess CO and the reaction proceeds at an 83.7% yield, what mass of iron can be obtained? 21

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