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Homework 6 posted and due Monday 3/5 Homework 7 posted and dues this Friday 3/9

Homework 6 posted and due Monday 3/5 Homework 7 posted and dues this Friday 3/9. Enjoyed snow day ???. Chemical Compositions from Combustion Data (continued).

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Homework 6 posted and due Monday 3/5 Homework 7 posted and dues this Friday 3/9

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  1. Homework 6 posted and due Monday 3/5 Homework 7 posted and dues this Friday 3/9 Enjoyed snow day ???

  2. Chemical Compositions from Combustion Data (continued) 2) A hydrocarbon sample (Cx Hy) is burned in oxygen producing 1.0 gram of CO2 and 0.4086 g H2O. What is the empiric formula for the hydrocarbon ? (C=12, O=16, H=1) ANSWER: CH2 CxHy CO2 + H2O mass 1 g 0.4086 g MW(g/mol) 44 18 mol 0.0227 0.0227 =mol C 2*0.0227= mol H

  3. A hydrocarbon,CxHy burns to form 22 g CO2 and 18 g H2O. What is the empiric formula of CxHy? • CH • CH2 • CH3 • CH4 • None of above

  4. A 3 g sample of a copper oxide is heated to drive off oxygen. On cooling 2.666 g of pure Cu remains. What is the copper oxide’s empiric formula ? • CuO2 • Cu2O • CuO • CuO3

  5. The mole road trip itinerary... • % composition problems and combustion analysis (pp. 94-103) • Reaction balancing (pp. 105-108). • Reaction stoichiometry predictions, limiting yields and % yields:moles level 3 ( pp. 108-123)

  6. How to Reaction balance (pp. 105-108) Essentially, just try to make elements balance by trial and error

  7. Chemical bookkeeping: balancing reactions old school (on blackboard) Example #1: Elementcombustion 2 2 Cu +O2  CuO Balanced !!!! 

  8. Reaction balancing (continued) Example #2: Organic combustion Balanced…at last !!!! C3H8+ O2  CO2+ H2O 5 3 4 Propane=LNG Liquid Natural Gas Helpful hint: first balance elements that appear in a single compound on both reactant and product sides.

  9. Slightly trickier balancing…the odd/even oxygen dilemma Internal combustion reaction 2 16 __C8H18 + __O2 __H2O + __ CO2 25 18 Octane = gasoline balanced

  10. More in-class equation balancing practice 4 1 __H3PO3 ___H3PO4 + ___PH3 3 Helpful hint: first balance elements that appear in a single compound on both reactant and product sides.

  11. More in-class equation balancing practice 9 6 2 2 __As2S3 + __O2__As2O3 + __SO2

  12. More in-class equation balancing practice 1 4 __H3PO3 ___H3PO4 + ___PH3 3 Helpful hint: first balance elements that appear in a single compound on both reactant and product sides.

  13. 14 13 12 2 ____C6H14 + ___O2 ___CO2 +___H2O Balance me, please !!! …On Board ( a trickier one…)

  14. The missing coefficient in the reaction: 2C8H18 + __O2 16CO2 + 18H2O • 50 • 34 • 32 • 25

  15. The mole road trip itinerary... • % composition problems and combustion analysis (pp. 94-103) • Reaction balancing (pp. 105-108) necessary prequel to moles level 3 • Reaction stoichiometry predictions, limiting yields and % yields: moles level 3 ( pp. 108-123)

  16. Reaction Stoichiometry problems: Moles level 3how chemists cook

  17. Reaction stoichiometry means following….. THE RECIPE

  18. THE RECIPE… 3 1 + 2 + 300 g/block 200 g/box 500 g/dozen 1900 g/souffle • How many boxes of cream to make 4 souffles ? 12

  19. Cooking and stoichiometry THE RECIPE 3 1 + 2 + 300 g/block 200 g/box 500 g/dozen 1900 g/souffle • 600 grams cheese makes how many souffles ? 2

  20. Cooking and stoichiometry THE RECIPE 3 1 + 2 + 300 g/block 200 g/box 500 g/dozen 1900 g/souffle 3000 g • How many grams of eggs combine with 9 boxes of cream ?

  21. Cooking and stoichiometry THE RECIPE 3 1 + 2 + 300 g/block 200 g/box 500 g/dozen 1900 g/souffle • 48 eggs combine with how many blocks of cheese? 2

  22. Simple mol-mol stoichiometry conversions C3H8 + 5O2-------- 3CO2 + 4H2O How many moles of O2 will burn to form 1.2 moles of CO2 ? Method 1: factor label way 1) given 2) want *5 mol O2 3 mol CO2 1.2 mol CO2 = ? mol O2 2 3) Use reaction stoichiometry coefficients in right ratio to cancel and connect…which ratio ???

  23. Mol-mol stoichiometry conversions (continued) Method 2: `mole ratios’ way C3H8 + 5O2-------- 3CO2 + 4H2O 1.2 mol ?? m Problem stated visually How many moles of O2will burn to form 1.2 moles of CO2 ? 1) ratio `wanted’ moles in numerator to given in denominator m 1.2 5 3 2) Set equal to matching coefficients for compounds given in reaction…which ??? = 1.2*m= 1.2 *5 1.2 3 = 2 3)Solve for m

  24. More complex stoichiometry problem done 2 ways MW 44 32 44 18 g/mol C3H8+ 5O2 3CO2+ 4H2O 22 grams of C3H8burned with O2 makes howmany grams of H2O ? Method 1: factor label 22 g C3H8 x 1 mole C3H8 44 g C3H8 4 mol H2O 1 mole C3H8 x 18 g H2O 1 mol H2O x = ?? g H2O 36

  25. 22 grams of C3H8burned with O2 makes howmany grams of H2O ? Method 2: mole ratio way (Board first) 44 32 44 18 g/mol Given: Problem stated visually C3H8+ 5O2 3CO2+ 4H2O ?? g 22 g

  26. 22 grams of C3H8burned with O2 makes howmany grams of H2O ? Method 2: mole ratio way 44 32 44 18 g/mol Given: Problem stated visually C3H8+ 5O2 3CO2+ 4H2O ?? g 22 g 0) convert all given masses & molecule counts to moles = 0.5 mol C3H8 22 g C3H8* 1 mol C3H8 44 g C3H8

  27. 22 grams of C3H8burned with O2 makes howmany grams of H2O ? Method 2: mole ratio way 44 32 44 18 g/mol Given: C3H8+ 5O2 3CO2+ 4H2O Problem stated visually ?? g 22 g = 0.5 mol C3H8 1) ratio `wanted’ moles m in numerator to given in denominator: = 4 1 m =mol H2O 0.5 mol C3H8

  28. 22 grams of C3H8burned with O2 makes howmany grams of H2O ? Method 2: mole ratio way 44 32 44 18 g/mol Given: C3H8+ 5O2 3CO2+ 4H2O ?? g 22 g 2) Solve for wanted moles m 0.5 = 4 1 0.5 * *0.5 = 2 mol H2O

  29. 22 grams of C3H8burned with O2 makes howmany grams of H2O ? Method 2: mole ratio way 44 32 44 18 g/mol Given: C3H8+ 5O2 3CO2+ 4H2O ?? g 22 g = 2 mol H2O 3) Convert wanted moles to wanted final units (grams) 2 mol H2O * 18 g H2O 1 mole H2O = 36 g H2O

  30. Practicing…clickers and not clickers

  31. C3H8 + 5O2--------3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol c)wtwt: How many grams of O2are needed to burn 1.1 g C3H8? • 0.8 • 4.0 • 0.25 • 0.16

  32. C3H8 + 5O2--------3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol e) count wt: How many grams of O2are needed to form 9*1022 molecules of H2O ? count wt • 1.0 g • 2.0 g • 1.5 g • 6.0 g

  33. C3H8 + 5O2--------3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol weight to moles How many moles of H2O form if 33 g of C3H8 are burned ? 3 mol H2O

  34. C3H8 + 5O2--------3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol f) weight to count How many molecules of CO2form if 1.592 g H2O results ? =4*1022

  35. C3H8 + 5O2--------3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol Mol count: How many molecules of O2does it take to form 0.020 moles of CO2 in the reaction above? (1 mol count=6*1023) • 1.2*1022 • 7.2*1021 • 1.0*1022 • 2.0*1022

  36. C3H8 + 5O2--------3CO2 + 4H2O 44 32 44 18 g/mol wtcount How many molecules of CO2are formed along with 0.40 g H2O in the reaction above.(1 mol count =6*1023) • 1.33*1022 • 1*1022 • 7.5*1021 • 4*1022

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