Exp 9: Analysis of a KClO3-KCl Mixture

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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
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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 (23
  ratio)
• 6 mol HCl is consumed to produce 2 mol AlCl3
  (ratio 31) and 3 mol H2 (ratio 21)
•  
• ? if 1 mol Al is consumed then only 1.5 mol H2 is
  produced (23 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

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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

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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
•  

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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

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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

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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
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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

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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

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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

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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 23
• 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

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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