Chapter 10 Stoichiometry

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1 Chapter 10 Stoichiometry Exercise 1 Show your work. For questions 1-4 use the equation: 2Mg + O 2 2MgO 1. Calculate the number of moles of oxygen needed to reaction with 6 moles of Mg. 6 mol Mg /1 mol O 2 = 3 mol O 2 1 / 2 mol Mg 2. Calculate the number of moles of MgO produced when 0.4 moles of oxygen react. 0.4 mol O 2 / 2 mol MgO = 0.8 mol MgO 1 / 1 mol O 2 3. Calculate the number of moles of MgO produced when 32 g of oxygen react. 32g O 2 /1 mol O 2 / 2 mol MgO = 2 mol MgO 1 / 32 g O 2 / 1 mol O 2 4. Calculate the grams of oxygen needed to produce 6 g of MgO. 6g MgO / 1 mol MgO/ 1 mol O 2 / 32g O 2 = 2.4 g O 2 1 / 40 g MgO / 2 mol MgO/ 1 mol O 2 For questions 5-9 use the equation: 2C 6 H O 2 12CO 2 + 6H 2 O 5. Calculate the number of moles of oxygen required to reaction with 5.00 mole of C 6 H mol C 6 H 6 / 15 mol O 2 = 37.5 mol O 2 1 / 2 mol C 6 H 6 6. Calculate the mole of CO 2 produced when 0.75 moles of O 2 react mol O 2 / 12 mol CO 2 / = 0.6 mol O 2 1 / 15 mol O 2 7. Calculate the number of grams of C 6 H 6 needed to produce 50.0 g of water. 50.0g H 2 O/ 1 mol H 2 O/ 2 mol C 6 H 6 / 78 g C 6 H 6 = 72.2 g C 6 H 6 1 / 18g H 2 O / 6 mol H 2 O / 1 mol C 6 H 6 8. Calculate the number of moles of water produced when 75 g of oxygen react. 75g O 2 / 1 mol O 2 / 6 mol H 2 O = 0.94 mol H 2 O 1 / 32g O 2 /15 mol O 2 H. Cannon, C. Clapper and T. Guillot Klein High School

2 9. Calculate the grams of C 6 H 6 need to produce 25 g of CO 2. 25g CO 2 / 1 mol CO 2 / 2 mol C 2 H 6 / 78g C 6 H 6 = 7.4g C 6 H 6 1 / 44g CO 2 /12 mol CO 2 / 1 mol C 6 H Calculate the number of grams of H 2 SO 4 produced when 27 g of water react with an excess of SO 3. H 2 O + SO 3 H 2 SO 4 27g H 2 O/ 1 mol H 2 O/ 1 mol H 2 SO 4 / 98 g H 2 SO 4 = 1 / 18g H 2 O / 1 mol H 2 O / 1 mol H 2 SO 4 Exercise 2 Show your work. 1. Calculate the number of moles of barium sulfate that can be prepared from 60.0 g of barium chloride. BaCl 2 + Na 2 SO 4 > BaSO 4 + 2NaCl 60.0g BaCl 2 / 1 mol BaCl 2 / 1 mol BaSO 4 = mol BaSO 4 1 / 208 g BaCl 2 / 1 mol BaSO 4 2. Calculate the number of moles of calcium chloride that would be necessary to prepare 85.0 g of calcium phosphate. 3CaCl 2 + 2Na 3 PO 4 > Ca 3 (PO 4 ) 2 + 6NaCl mol CaCl 2 3. Sodium chloride (0.400 Mole) is allowed to react with an excess of sulfuric acid. How many moles of hydrogen chloride could be formed? 2NaCl + H 2 SO 4 > Na 2 SO 4 + 2HCl mol HCl 4. If mole of barium nitrate is allowed to react with an excess of phosphoric acid, how many moles of barium phosphate could be formed? 3Ba(NO 3 ) 2 + 2H 3 PO 4 > Ba 3 (PO 4 ) 2 + 6HNO mol Ba 3 (PO 4 ) 2 5. Calculate the number of grams of carbon dioxide produced from the burning of 1.65 moles of C 3 H 8. C 3 H 8 + 5O 2 > 3CO 2 + 4H 2 O 218g CO 2 6. How many moles of hydrogen molecules could be produced by the reaction of 3.40 moles of sodium atoms with water? 2Na + 2H 2 O > 2NaOH + H mol H 2 7. How many moles of HI would be necessary to produce 2.20 moles of iodine, according to the following balanced equation: 4.4 mol HI 10-2

3 10 HI + 2KMnO 4 + 3H 2 SO 4 > 5 I 2 + 2MnSO 4 + K 2 SO 4 + 8H 2 O 8. Calculate the number of grams of zinc chloride that can be prepared from 34.0 g of zinc. Zn + 2HCl > ZnCl 2 + H g Zn/ 1 mol Zn/ 1 mol ZnCl 2 / 136g ZnCl 2 = 71.1g ZnCl 2 1 / 65g Zn / 1 mol Zn / 1 mol ZnCl 2 Exercise 3 Show your work. 1. If 20.0 g zinc reacts with excess hydrochloric acid, how many grams of zinc chloride are produced? Zn + HCl ZnCl 2 + H 2 2. How many grams of chlorine must be reacted with excess sodium iodide if 10.0 g sodium chloride is needed? NaI + Cl 2 NaCl + I 2 3. How many grams of oxygen are produced in the decomposition of 5.0 g of potassium chlorate? KClO 3 KCl + O 2 4. How many grams of copper are required to replace 4.0 g of silver nitrate which is dissolved in water? Cu + AgNO 3 Cu(NO 3 ) 2 + Ag 5. If excess ammonium sulfate reacts with 20.0 g of calcium hydroxide, how many grams of ammonia are produced: (NH 4 ) 2 SO 4 + Ca(OH) 2 CaSO4 + NH 3 + H 2 O 6. If excess sulfuric acid reacts with 30.0 g of sodium chloride, how many grams of hydrogen chloride are produced? NaCl + H 2 SO 4 HCl + Na 2 SO 4 7. How much silver phosphate is produced if 10.0 g of silver acetate is reacted with excess sodium phosphate? AgC 2 H 3 O 2 + Na 3 PO 4 Ag 3 PO 4 + NaC 2 H 3 O 2 8. What amount of sodium hydroxide is needed to completely neutralize 10-3

4 25.0 g of sulfuric acid? NaOH + H 2 SO 4 Na 2 SO 4 + H 2 O 9. Copper (II) sulfate pentahydrate may be heated to drive off the water of hydration. If 5.0 g of water is produced, what was the mass of the original compound? CuSO 4 5H 2 O CuSO 4 + 5H 2 O 10. How many moles and how many grams of magnesium phosphate are produced by starting with g of phosphoric acid and an excess of magnesium carbonate? H 3 PO 4 + MgCO 3 Mg 3 (PO 4 ) 2 + CO 2 + H 2 O Exercise 4 1. Aluminum and iron (III) oxide react according to the following equation 2Al + Fe > A Fe How much iron would be produced from 52.5g of iron (III) oxide? 52.5g Fe 2 O 3 / 1mol Fe 2 O 3 / 2 mol Fe / 56 g Fe = 36.8g Fe 1 / 160g Fe 2 O 3 / 1 mol Fe 2 O 3 / 1 mol Fe 2. Ammonia is produced according to the following equation: N 2 + H 2 NH 3 How many kilograms of nitrogen would be required to produce 556 kilogram5 of ammonia? 3. Calcium carbide is made in an electric furnace according to the ecuation: CaO + C CaC 2 + CO 75.5 kg of CaO will produce how many kilograms of calcium carbide? 4. In the equation Fe + H 2 O Fe 2 O 3 + H 2 235g of iron will produce how many grams of iron (III) oxide? 5. Calcium chloride and water react according to the following equation CaCl 2 + H 2 O CaO + HC1 How much hydrogen chloride would be produced from 37 4g of calcium chloride? 10-4

5 6. how many grams. of iron (ii) bromide will be: neeced to react with an excess of potassium phosphate to produce 17.1g of solid iron(ii) phosphate? 7. How many grams of oxygen gas are required to react with 37.8g of solid zinc iodide, to produce solid iodine and solid zinc oxide? 2ZnI 2 + O 2 --> 2ZnO + 2I g ZnI 2 / 1 mol ZnI 2 / 1 mol O 2 / 32g O 2 = 1 / 319g ZnI 2 / 2 mol ZnI 2 / 1 mol O 2 8. How many grams of silver can be produced by the reaction 5.05g of silver nitrate with excess copper? 9. What mass of barium chloride will be needed to react completely with 113g of aluminum sulfate to produce barium sulfate and aluminum chloride? 10. What mass of carbon dioxide will be produced by the combustion of of pentane, C 5 H 12? C 5 H O 2 --> 5CO 2 + 6H 2 O 40.09g C 5 H 12 /1 mol C 5 H 12 / 5 mol CO 2 / 44g CO 2 = 122.5g CO 2 1 /72 g C 5 H 12 / 1 mol C 5 H 12 / 1 mol CO How many grams of copper (II) nitrate would be produced from 4.30g of copper metal reacting with excess hydrogen nitrate? 12. When copper (II) nitrate reacts with sodium hydroxide, copper (II) hydroxide is produced along with sodium nitrate. How many grams of copper (II) hydroxide can! be prepared from 12.7g of copper (II) nitrate and excess sodium hydroxide? 13. When copper (II) hydroxide is heated it decomposes to black copper (II) oxide and water. How many grams of copper (II) oxide will be formed from the decomposition of 6.99g of copper(ii) hydroxide? 10-5

6 14. When 5.37g of the black copper(ii) oxide is mixed with excess hydrogen sulfate, the solution turns a clear blue, indicating the formation of copper (I) sulfate. How many grams of copper (II) sulfate will be formed in this double displacement reaction? 15. If an excess of zinc metal is placed in a copper (II) sulfate solution, the zinc will displace the copper. if 10.8g of copper(ii) sulfate are reacted, how many grams of copper metal will be recovered from the solution? Exercise 5 1. Calculate the mass of O 2 produced if 2.50 g of KC1O 3 decomposes to produce potassium chloride and oxygen. 2. If 20.0 g of magnesium react with excess hydrochloric acid, how many grams of magnesium chloride are produced? 3. How many grams of chlorine gas must be reacted with excess sodium iodide if 10.0 g of sodium chloride are needed? 4. How many grams of oxygen are produced in the decomposition of 5.00 g of potassium chlorate? 5. What mass of copper is required to replace silver from 4.00 g of silver nitrate? The products are copper (II) nitrate and silver. 6. If excess ammonium sulfate reacts with 20.0 g of calcium hydroxide, how many grams of ammonia are produced? The other products are water and calcium sulfate. 7. If excess sulfuric acid (H 2 SO 4.) reacts with 30.0 g of sodium chloride, how many grams of hydrogen chloride are produced? 10-6

7 8. How much silver phosphate is produced if 10.0 g of silver acetate react with excess sodium phosphate? 9. How many grams of sodium hydroxide are needed to completely neutralize 25.0 g of sulfuric acid? 10. Molten iron and carbon monoxide are produced in a blast furnace by the reaction of iron (III) oxide and coke (carbon). If 25.0 kg of pure iron (III) oxide are used, how much iron can be produced? Exercise 6 Show your work 1. Copper oxide is reduced by ammonia according to the following equation: 3CuO + 2 NH 3 ---> 3Cu + N 2 + H 2 O What mass of nitrogen in grams is. obtained by the reduction of 120g of CuO? 2. Sulfur may be oxidized by potassium dichromate according to the following equation 2K 2 Cr 2 O 7 + H 2 O + 3S > 3SO 2 + 4KOH +2.Cr 2 O 3 What mass of sulfur wil1 be oxidized by 12 grams of potassium dichromate? 3. How many grams of BaSO 4 may be precipitated from a solution containing.314 grams of sodium sulfate? BaC1 2 + Na 2 SO NaC1 + BaSO 4 4. Consider the following equations: 3CaC K 3 PO > Ca 3 (PO4) 2 + 6KCl a. 87g of CaC1 2 will produce? _ grams of KC

8 b. How many grams of K 3 PO 4 can 132g of CaC1 2 react? 5. When the neutralization of H 3 PO 4 with Ca(OH) 2 occurs, then the following equation exists. H 2 PO 4 + Ca (OH) > Ca 3 ( PO 4 ) 2 + H 2 O a) 8.4 moles H 3 PO 4 produces _? moles of water. b) 18 moles of Ca 3 (PO 4 ) 2 is produced from? moles of Ca(0H) Solve the following from the given equation: Bi 2 (SO4) 3 + 6NH 4 OH ----> 2Bi(OH) 3 + 3(NH4) 2 SO4 If you are given 352g of Bi 2 (SO4) 3, then: a) Calculate the number of moles of Bi 2 (SO4) 3. b) How many moles of Bi(OH) 3 will be produced from the 352g of Bi 2 (S0 4 ) 3? c) How many moles of NH 4 OH will react with the 352g of Bi 2 (SO4) 3? 7. Methane gas can be prepared in the laboratory by the following reaction: A1 4 C H 2 O --> 3CH 4 + 4Al(OH) 3 a) What weight of Al 4 C 3 is needed to prepare 1.8 moles of aluminum hydroxide? b) How many grams of methane will be produced from 30g of water?. 8. What weight of oxygen is needed to burn 31 grams of propane gas? C 3 H 8 + O 2 CO 2 + H 2 O (unbalanced) 10-8

9 9. In the process of photosynthesis, plants use carbon dioxide and water to produce sugars according to the over-all reaction. 11 H 2 O + 12 C0 2 C 12 H 22 O 11? a) What weight of carbon dioxide is used by a plant in making 254g of sugar C 12 H 22 O 11? b) How many grams of oxygen will 8O grams of carbon dioxide produce? Exercise 7 Show your work QUESTIONS 1,2,3:REFER TO THE FOLLOWING EQUATION: Cu + HNO 3 Cu(NO 3 ) 2 + NO + H 2 O 1. If you could drop 12 atoms of copper into a beaker containing hydrogen nitrate, how many molecules of nitrogen dioxide would be produced? 2. Calculate the number of moles of water produced when 6.6 moles of copper (II) nitrate are formed on the reaction. 3. How many grams of copper would be needed to react with 4 moles of hydrogen nitrate? 4. 25g of potassium chlorate is to be decomposed by heating. How many grams of oxygen can be prepared? KClO 3 ---> KC1 + O 2 5. In a reaction between sulfur and oxygen, 80g of sulfur dioxide is formed. How many grams of sulfur were burned? 6. How many grams of hydrogen are required to completely convert 25g of hot magnetic iron (III) oxide (Fe 2 O 3 ) to elementary iron? Fe 2 O 3 + H 2 Fe + H 2 O 10-9

10 7. How many grams of chlorine will it take to react with 68g of potassium iodide? 8. Approximately 130g of zinc was dropped into a solution containing HC1. How many moles of hydrogen were produced? Zn + HC1 ZnC1 2 + H 2 9. Suppose 10g of iron (II) sulfide is treated with enough hydrogen chloride to complete the reaction. How many grams of hydrogen sulfide gas could be collected? FeS + HC1 FeC1 2 + H 2 S 10. A portable hydrogen generator utilizes the reaction: CaH 2 + 2H 2 O Ca(OH) 2 How many grams of hydrogen can be produced by a 50g cartridge of CaH 2? 11. How much ferric oxide will be produced by the complete oxidation of grams of iron? The reaction is: Fe + O 2 Fe 2 O Chloropicrin, CC1 3 NO 2, can be made cheaply for use as an insecticide by a process which utilizes the reaction: CH 3 NO 2 + 3C1 2 CC1 3 NO 2 + 3HC1 How much nitromethane, CH 3 NO 2, is needed to form 500.0g of chloropierin? 13. Ethyl alcohol (C 2 H 5 OH) is made by the fermentation of glucose (C 6 H 12 O 6 ) as indicated by the equation: C 6 H 12 O 6 2C 2 H 12 OH + 2CO 2 How many grams of carbon dioxide gas can be produced from 60.0g of ethyl alcohol? 10-10

11 14. One of the reaction used in the petroleum industry for improving the octane rating of fuels is: C 7 H 14 C 7 H 8 + 3H 2 If 56.8 grams of heptane (C 7 H 14 ) is used how much hydrogen is produced? 15. When copper is heated with an excess of sulfur, copper (I) sulfide is produced. How many grams of copper (I) sulfide could be produced from 100 grams of copper? Limiting Reactants 1. If 20.0g of sodium hydroxide react with 30.0 g of sulfuric acid to produce sodium sulfate, which reactant is limiting? How much sodium sulfate is produced? 2NaOH + H 2 SO 4 --> Na 2 SO 4 + 2H 2 O 20.0g NaOH/ 1 mol NaOH/ 1 mol H x SO 4 / 98g H 2 SO 4 1 / 40g NaOH / 2 mol NaOH /1 mol H 2 SO 4 = 24.5g H 2 SO 4 needed to completely use the 20.0g of NaOH, while we HAVE 30.0g of H 2 SO 4 ; thus the H 2 SO 4 is in excess and NaOH is limiting 20.0g NaOH/ 1 mol NaOH/ 1 mol Na x SO 4 / 142g Na 2 SO 4 = 35.5g Na 2 SO 4 1 / 40g NaOH / 2 mol NaOH / 1 mol Na 2 SO 4 2. What reactant is limiting is 3.00 g of chlorine gas reacts with 25.0 g of sodium bromide to produce bromine gas? How much sodium chloride is produced? 3. If 20.0 g of potassium hydroxide reacts with 15.0 g of ammonium sulfate, how much ammonia is produced (the other products are potassium sulfate and water). Which reactant is limiting? 2KOH + (NH 4 ) 2 SO 4 --> 2NH 3 + K 2 SO 4 + 2H 2 O 20.0g KOH/ 1 mol KOH/ 1 mol (NH 4 ) 2 SO 4 / 132g (NH 4 ) 2 SO 4 1 / 56g KOH / 2 mol KOH / 1 mol (NH 4 ) 2 SO 4 = 25.6g (NH 4 ) 2 SO 4 needed to completely use the 20.0g KOH Since you have only 15.0g (NH 4 ) 2 SO 4 (less than needed) the (NH 4 ) 2 SO 4 is the limiting reactant 10-11

12 4. If a drain cleaner contains 455 g of sodium hydroxide and 45.0 grams of aluminum shavings, when this is reacted with water, how much hydrogen gas would be produced (the other product is sodium aluminate (AlO 2-1 )? What is the limiting reactant? 5. If 23.4 g of sodium hydroxide reacts with 50.0 g of hydrochloric aced, how much water will be produced? What is the limiting reactant? 6. How much chromium (III) hydroxide will be produced by the reaction of 2.37 g of silver nitrate with 2.00 g of sodium hydroxide? 7. When 84.1 g of magnesium oxide reacts with 47 g of water, how much magnesium hydroxide is formed? What is the limiting reactant? 8. If 261 g of potassium chloride reacts with 543 g of silver nitrate, how much silver chloride will be produced? 9. Calculate the number of grams of carbon dioxide which will be formed in the reaction between 10.0 grams of propane (C 3 H 8 ) and 10.0 grams of oxygen. 10. In the reaction single replacement reaction between gold III sulfide and hydrogen gas if the initial amount of Au 2 S 3 is g and the initial amount of H 2 is 5.67g, what is the final mass of gold? 10-12

13 11. In a reaction between magnesium nitride and water, magnesium hydroxide and ammonia (NH3) are produced. If the initial amount of Mg 3 N 2 is 58.1g and the initial amount of H 2 O is 20.4g, what is the final mass of ammonia? 12. In the reaction 2C 3 H 6 + 2NH 3 + 3O 2 2C 3 H 3 N + 6H 2 O, if the initial amounts are C 3 H 6 : 22.5g, NH 3 : 20.6 g, and O 2 : 18.1 g, what are the final amounts of each product? 13. What is the limiting reactant when 19.9g of CuO are exposed to 2.02g of H 2 according to the following equation? CuO(s) + H 2 (g) Cu(s) + H 2 (g) How many grams of Cu are produced? 14. Metallic magnesium reacts with steam to produce magnesium hydrocise and hydrogen ga. If 16.2 g of Mg are heated with 12.0 g of H 2 O, what is the limiting reactant? How many grams of each product will be produced? Percent Yield 1. In the double displacement reaction between citric acid and plumbic hydroxide, how much lead (IV) citrate would be produced from 87.6g of citric acid and 111g of plumbic hydroxide if the percent yield is 83%? This is both a limiting reactant and a % yield problem. First you must determine which is the limiting, then apply the % yield. 4H 3 C 6 H 5 O 7 + 3Pb(OH) 4 --> Pb 3 (C 6 H 5 O 7 ) 4 + 6H 2 O 87.6g H 3 C 6 H 5 O 7 / 1 mol H 3 C 6 H 5 O 7/ / 3 mol Pb(OH) 4 / 275g Pb(OH) 4 1 / 192g H 3 C 6 H 5 O 7 / 4 mol H 3 C 6 H 5 O 7 / 1 mol Pb(OH) 4 = 94.1g Pb(OH) 4 needed to completely use the 87.6g of H 3 C 6 H 5 O 7, and you have 111g of the Pb(OH) 4 so it is the excess, while H 3 C 6 H 5 O 7 is the limiting

14 Now we use the H 3 C 6 H 5 O 7 to calculate how much Pb 3 (C 6 H 5 O 7 ) 4 will be produced 87.6g H 3 C 6 H 5 O 7 /1 mol H 3 C 6 H 5 O 7/ /1 mol Pb 3 (C 6 H 5 O 7 ) 4 /1377g Pb 3 (C 6 H 5 O 7 ) 4 1 / 192g H 3 C 6 H 5 O 7 / 4 mol H 3 C 6 H 5 O 7 / 1 mol Pb 3 (C 6 H 5 O 7 ) 4 = 157.1g Pb 3 (C 6 H 5 O 7 ) 4 - this is a theoretical value since it is calculated from an amount of a reactant. In a reaction with an 83% yield, the actual amount of Pb 3 (C 6 H 5 O 7 ) 4 would be 130.4g (1.30 x 10 2 ) 2. When potassium chromate is added to g of silver nitrate, solid silver chromate is formed. If the mass of the silver chromate formed is g, what is the percent yield of the reaction? 3. Magnesium chloride can be produced by reacting magnesium hydroxide with hydrochloric acid. If g of magnesium chloride is produced from 185 g of hydrochloric, what is the percent yield of the reaction? 4. In the double displacement reaction between acetic acid and plumbic hydroxide, how much lead (IV) acetate would be produced from 76.8g of acetic acid if the percent yield is 91%? 5. When 84.8 g of ferric oxide reacts with an excess of carbon monoxide, 54.3 g of iron is produced, along with carbon dioxide gas. What is the percent yield of this reaction? 6. Chlorobenzene, C 6 H 5 Cl, is used in the production of many important chemicals, such as aspirin, dyes and disinfectants. One industrial method of preparing chlorobenzene is to react benzene. C 6 H 6, with chloring, as represented by the following equation. C 6 H 6 (l) + Cl 2 (g) C 6 H 5 Cl (s) + HCl (g) When 36.8g of C 6 H 6 react with an excess of Cl 2, the actual yiel2os e;ectrp;yzed to produce Mg and Cld of C 6 H 5 Cl is 38.8 g. what is the 10-14

15 percent yield of C 6 H 5 Cl? 7. Magnesium is obtained from sea water. Ca(oh) 2 is added to sea water to precipitate Mg(OH) 2. The precipitate is filtered and reacted with HCl to produce MgCl 2. the MgCl 2. If g of magnesium are recovered from g of MgCl 2, what is the percent yield for this reaction? 8. Aluminum hydroxide is often present in antacids to neutralize stomach acid (HCl). If 14.0 g of Al(OH) 3 is present in an antacid tablet, determine the theoretical yield of aluminum chloride produced when the tablet reacts with stomach acid. If the actual yield of aluminum chloride from this tablet is 22.0 g, what is the percent yield? Al(OH) 3 (s) + 3HCl (aq) AlCl 3 (aq) + 3H 2 O (l) 9. Zinc reacts with iodine in a synthesis reaction. Write the balanced chemical equation for the reaction. Determine the theoretical yield if a g sample of zinc was used. Determine the percent yield if 515.6g is recovered. 10. Upon heating, calcium carbonate decomposes into calcium oxide and carbon dioxide gas. What is the theoretical yield of CO 2 if g of CaCo 3 is heated? What is the percent yield of CO 2 if 97.5 g of CO 2 is collected? 11. Chlorine can be prepared by the reaction of manganese )II) oxide with hydrochloric acid. MnO 2 (s) + HCl (aq) MnCl 2 (aq) + Cl 2 (g) + H 2 O (l) Balance the equation and determine the percent yield of chlorine if 86.0 g of MnO 2 and 50.0 g of HCl react to form 20.0 g of chlorine

16 Exercise 8 Show your work. Indicate if the following are endothermic or exothermic: 1. C + H 2 0 C H kj 2. C+ 1/ kj CO 3. CO+ 1/20 2 CO kj 4. N kj 2NO 2 5. Given the following balanced equation: H 2 + F 2 ---> H 2 F x 10 5 J a. Is the reaction exothermic or endothermic? b. Calculate the number of joules of heat energy produced in the reaction of 37.0 g of fluorine gas with sufficient hydrogen gas. 6. Given the following balanced equation: O 2 + 2F 2 ---> 2OF x 10 4 J a. Is the reaction exothermic or endothermic? b. Calculate the number of grams of fluorine gas needed for the reaction with 8.74 x 10 3 J of heat energy and sufficient oxygen gas

17 Exercise 9 Mass-Energy Problems Stiochiometry Exercise mass-energy 1. A rocket fuel is prepared by reacting hydrazine and dinitrogen tetroxide according to the equation: 2N 2 H 4 + N 2 O 4 3N 2 + 4H kj Calculate the heat released when 3200 grams of hydrazine are consumed in the rocket engine. 3200gN 2 H 4 / 1 mol N 2 H 4 / 2400KJ = 1.2 x 10 5 KJ 1 / 32g N 2 H 4 / 2 mol N 2 H 4 2. The dissociation of ammonia into its elements is an endothermic reaction that absorbs 92.2kj of energy per mole of nitrogen. How much energy will be required to decompose 85.0 grams of ammonia? 3. Given the equation: Fe 2 O 3 + 2Al Al 2 O 3 + 2Fe kj How much energy is produced by the reaction of 16.0 grams of iron (III) oxide with excess aluminum metal? 4. When hydrogen peroxide is placed on a cut knee it decomposes spontaneously into water and oxygen gas, releasing 200 kj of heat per mole of oxygen. How much energy will be released when 34.0 grams of hydrogen peroxide decomposes? 5. Manganese will react with hydrochloric acid to produce hydrogen gas according to the reaction: Mn + 2HCl MnCl 2 + H kj How much energy will be released when g of manganese reacts completely? 10-17

18 Stiochiometry Exercise mass-energy Molar Relationship in a Chemical Reaction Problem: To compare the amount of sodium bicarbonate that reacts with hydrochloric acid to the amount of sodium chloride produced. Procedure: 1. Determine the mass of a clean evaporating dish and watch glass (together) 2. Weigh out approximately 3 grams of sodium bicarbonate into the dish (record exact amount) 3. Obtain approximately 6 ml of hydrochloric acid. This is a small test tube filled to the lower edge of the marking spot. The exact amount is not important, as this reactant will be in excess. 4. With a dropper, slowly and carefully add the acid to the dish through the space between the lip and the watch glass. Add acid only until the reaction stops and you are left with a clear colorless solution that is no longer bubbling. 5. Tilt the dish to be sure the acid has reached all of the solid 6. Place the dish with watch glass cover on a ring above a burner. Heat slowly to keep at a low boil until the solution is dry. Spattering is the result of heating too fast, and will result in the loss of some of your product. Heat until NO liquid remains on the watch glass cover. 7. Let the apparatus cool and determine it s mass again. 8. Time permitting, reheat to boil away any water left, coo, reweigh. 9. Clean all laboratory apparatus and return to proper storage area. Questions to consider: 1. How many moles of sodium bicarbonate were used? 2. Using the equation NaHCO 3 + HCl NaCl + H 2 O + CO 2, predict the moles and grams of sodium chloride you should have produced. 3. How many moles of sodium chloride were actually produced? 4. What is your percent experimental error? 5. Do your results verify the stoichiometry of the reaction? Explain 6. Do your results verify the Law of Conservation of Mattter? 10-18

19 Chapter 10 Quantitative Analysis Lab Objective: To produce a specific quantity of lead (II) chromate by the reaction of lead (II) nitrate with potassium chromate; and to demonstrate the Law of Conservation of Matter and the stoichiometric relationship of the reaction. Procedure: (remember to record all measurements and observations in your lab book`) 1. Prelab calculations a. Choose a number between 1.00 and This is the number of grams of lead (II) chromate you will try to make. b. Calculate the number of moles of lead chromate equal to your number of grams. c. Calculate the number of moles of lead(ii) nitrate required to give the above number of moles of lead chromate. d. Calculate the number of grams of potassium chromate required to-give the above number of moles of lead (II) chromate? 2. Lab - Day 1 a. Carefully weigh out exactly the calculated amount of lead (II) nitrate. Dissolve in about 25 ml of distilled water in a 100 ml beaker. The exact amount of water is not critical since it will be removed by drying. b. In a 150 ml beaker carefully weigh the calculated amount of potassium chromate. Dissolve in about 25 ml of water. Again the exact amount of water is not critical to the reaction. c. Combine the two solutions to begin the reaction, being certain to rinse all of the solution from the beaker. d. Stir the reaction for 3-4 minutes to coagulate the precipitate. e. Filter the solution

20 f. Spread the filter paper out to dry overnight. g. Time permitting, evaporate the contents of the beaker and reweigh 3. Lab - Day 2 a. Determine the mass of both products of the reaction. b. Calculate the number of moles of lead (II) chromate and potassium nitrate produced, and correlate this to the stoichiometry of the equation. (Divide each of these by the moles of lead (II) nitrate. To what numbers in the equation should these relate? c. Calculate the number of grams of potassium nitrate and lead (II) chromate produced. Have you illustrated the conservation of mass? Explain d. Calculate your percent yield. e. If your yield was below 98% or above 101%, suggest possible explanations. Lab report include a list of all measurements, show work on all calculations (number these to correlate with the steps in the procedure, don't forget to label with units). There should be a total of 8 calculations in your report (follow the steps in the procedure). Your grade will be based on laboratory accuracy (from your percent yield) as well as mathematical accuracy (from your calculations work)

21 Exercise Lab 10-21

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