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Exp 9: Analysis of a KClO 3 -KCl Mixture

Exp 9: Analysis of a KClO 3 -KCl Mixture. Introduction Small amounts of O 2 can be generated from decomposition reaction 2BaO 2 (s) 2BaO (s) + O 2 (g) 2KClO 3 (s)  2KCl (s) + 3O 2 (g) Manganese oxide (MnO 2 ) is a catalyst Objectives

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Exp 9: Analysis of a KClO 3 -KCl Mixture

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  1. Exp 9: Analysis of a KClO3-KCl Mixture • Introduction • Small amounts of O2 can be generated from decomposition reaction • 2BaO2(s)2BaO(s) + O2(g) • 2KClO3(s)  2KCl(s) + 3O2(g) Manganese oxide (MnO2) is a catalyst Objectives • Study thermal decomposition of potassium chlorate, KClO3 • Identify product of reaction from the changes in mass of the reactant • Perform calculations based on balanced equations D D MnO2

  2. Exp 9: Analysis of a KClO3-KCl Mixture • Balancing equations 2 Al(s) + 6 HCl(aq)  2 AlCl3 (aq) + 3 H2(g) 2 mol Al(s) + 6 mol HCl(aq)  2 mol AlCl3 (aq) + 3 mol H2(g) • Balanced reaction equation is a mole statement  2 mol Al is consumed to produce 3 mol H2 (2:3 ratio) • 6 mol HCl is consumed to produce 2 mol AlCl3 (ratio 3:1) and 3 mol H2 (ratio 2:1)  if 1 mol Al is consumed then only 1.5 mol H2 is produced (2:3 ratio) • Molar ratios 2 mol Al / 6 mol HCl 6 mol HCl / 3 mol H2 2 mol AlCl3 / 3 mol H2 6 mol HCl / 2 mol AlCl3

  3. Exp 9: Analysis of a KClO3-KCl Mixture • Remember • If you need quantities in gram: convert mole to grams by multiplying by molar mass • If you need mol: convert gram to mole by dividing by the molar mass

  4. Exp 9: Analysis of a KClO3-KCl Mixture • Calculations with balanced equations, use molar ratios   2 Al(s) + 6 HCl(aq)  2 AlCl3 (aq) + 3 H2(g) 2 mol Al  2 mol AlCl3 + 3 mol H2     1 mol Al  1 mol AlCl3 + 1.5 mol H2 How many mole of Al to produce 5 mol H2?  2 mol Al/3 mol H2 * 5 mol H2 = 3.333 mol Al

  5. Exp 9: Analysis of a KClO3-KCl Mixture Calculations with balanced equations • What mass of Al to produce 5.00 g H2? • Step 1)      convert mass H2 to mol H2 • Step 2)      Calculate amount of Al in mol based on molar ratio • Step 3)      Calculate amount of Al in g, based on molar mass of Al • 5.00 g H2 = 5.00 g / 2.00 g/mol H2 = 2.50 mol H2 • Molar ration Al/H2 = 2 mol Al per 3 mol H2  2.50 mol H2 = 2.50 mol * 2/3 * 1 mol Al = 1.67 mol Al Molar mass of Al = 27.3 g/mol  mass of Al in g = 1.67 mol * 27.3 g/mol = 45.50 g Al

  6. Exp 9: Analysis of a KClO3-KCl Mixture How much AlCl3 is produced? • 2 mol Al produces 2 mol AlCl3 • molar mass of AlCl3 = molar mass of Al + 3 x molar mass of Cl = 27.3 g/mol + 3 x 35.45 g/mol = 133.65 g/mol AlCl3 • 1.67 mol Al * (2 mol AlCl3/2 mol Al) * 133.65 g/mol = 223.20 g AlCl3

  7. Exp 9: Analysis of a KClO3-KCl Mixture Procedure: • Determine the amount of KClO3 in a mixture of KClO3 and KCl by determining the change in mass when O2 is released • Calculate the molar mass based on the molar ratio of KClO3 and O2 in the balanced equation • 2KClO3(s)  2KCl(s) + 3O2(g) • KCl(s)  no reaction (there is no O2 to evolve!) • The amount of KClO3 decreases, whereas the amount of KCl increases • The amount of KClO3 decomposed is proportional to the amount of O2 generated • The amount of O2 generated is proportional to the amount of weight loss of the whole sample D MnO2 D MnO2

  8. Exp 9: Analysis of a KClO3-KCl Mixture Procedure: • Put a small amount (1-2 g) of MnO2 (catalyst) in a test tube and heat over a hot flame for ~ 5 min to drive out moisture and organic components (explosion risk) • Cool test tube + MnO2 to room temperature • Weigh test tube on a balance, and record mass • Add KClO3 + KCl mixture to tube, mix thoroughly and weigh tube again

  9. Exp 9: Analysis of a KClO3-KCl Mixture Experimental • Clamp tube in a clamp in a ringstand under 45o angle • Heat contents with a moderate flame • If white smoke evaporates, remove flame • This is KCl that evaporates and escapes and it will affect your results! • After about 8 minutes, heat the mixture with a hot flame for about 10 more minutes • Allow the tube to cool to room temperature • Weigh the test tube with the mixture

  10. Exp 9: Analysis of a KClO3-KCl Mixture Procedure: • Reheat for an additional 10 minutes and weigh again to make sure that all O2 was driven out • Two successive heatings need to result in a difference of 0.05 g in weight or less • Use the results of the last weighing to calculate the mass of O2 and the mass of KClO3

  11. Exp 9: Analysis of a KClO3-KCl Mixture Calculations: 2KClO3(s)  2KCl(s) + 3O2(g) Mass of O2 evolved = = mol O2 Molar ratio of KClO3 : O2 = 2:3 Moles of KClO3 = = mol KClO3 = grams KClO3 Mass of KCl = Total mass – gram KClO3 = = grams KCl %KClO3 = mass KClO3/total mass (KClO3 + KCl) *100% = % KClO3 %KCl = mass KCl/total mass (KClO3 + KCl) * 100% = %KCl

  12. For next class • Results and answers due next week 04/9/13 • Format: See ACES or class website • Include report sheet and calculations • Use your critical thinking skills to discuss errors • Pre-lab next week: Absorption Spectrum

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