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Homework 8: Ad Dahna Desert Challenge - Limiting Yield Calculations

This homework assignment focuses on limiting yield calculations in chemistry, using examples and applying them to real-world scenarios. Students will practice calculating theoretical yields and percent yields.

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Homework 8: Ad Dahna Desert Challenge - Limiting Yield Calculations

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  1. Homework 8: posted and due this Friday (put on chair outside Doc’s door: PHS 305 Yay !!! Kitty is happy !!!! No Chem class this Friday: Alfred State Science Fair Day (Orvis): Mole bucks for interviewing two participants (See form)

  2. A non-chemical example of a `limiting’ yield problem You have gotten lost on the Ad Dahna desert –largest desert on the Saudi peninisula. To avoid perishing you must reach the nearest oasis which is 100 km away. You can walk at maximum 10 km/ day. You need to consume at least 2 liters of water and ½ kg of food per dayto walk that distance. You have in your pack: • 16 liters of water • 5 kg of food • Broken cell phone What’s the maximum distance you can expect to travel ??

  3. Food Calculation 5 kg food = 10 days ½ kg/day =>10 days * 10 km = 100 km  day

  4. Water Calculation 16 liters = 8 days 2 liters/day • 8 days * 10 km = 80 km  day The winner is….always the smaller one… it limits.

  5. 3 examples of limiting yield calculationsvia the `cut and try’ approach (on board) example #1:mol-mol 5O2 + C3H83CO2 + 4H2O mol 0.33 0.1 ?? mol Given 0.33mol O2 and 0.10 mol C3H8, compute the maximum theoretical yield of CO2 moles Ans. 0.2 mol CO2 (O2 limits)

  6. 5O2 + C3H8 3CO2+ 4H2O Mol 0.7 0.125 mol ? How many mol of H2O form from burning 0.125 mol C3H8 with 0.7 mol O2 ? • 0.56 mol • 0.50 mol • 0.42 mol • 0.375 mol

  7. The `cut & try’ approach to limiting yield calculations (cont.) 0.18 g H2O (O2 limits) example #2: wt-wt 5O2 + C3H83CO2 + 4H2O g 4.0 2.2 ? g MW 32 44 44 18 Given 4.0 grams O2 and 2.2 grams C3H8, compute the theoretical yield of H2O in grams for the combustion shown above.

  8. 2C8H18 + 25O2 -------- 16CO2 + 18H2O MW 114 g/mol 32 g/mol 44 g/mol 18 g/mol w(g) 3.24 1.136?? g Given 3.24 g C8H18 and 1.136 g O2, how many grams of CO2form ? • 10.0 g • 1.0 g • 0.11 g • 1.56 g

  9. Cut and try approach example #3: mixed  grams C12H22O11 + 12O2 -------- 12CO2 + 11H2O MW 342 g/mol 32 g/mol 44 g/mol 18 g/mol w(g)68.40 72.73 ?? g How many grams of CO2 will be produced if 1023 molecules of sucrose, C12H22O11, are combined with 72.73 grams of O2 according to the balanced equation above? 100 g CO2 (O2 limits)

  10. 2C8H18 + 25O2 -------- 16CO2 + 18H2O MW 114 g/mol 32 g/mol 44 g/mol 18 g/mol w(g) 3.24 1.136?? g Given 1.705*1022 molecules of C8H18 and 1.136 g O2, how many grams of CO2form ? • 10.0 g • 1.0 g • 0.11 g • 1.56 g

  11. Need more practice ???

  12. % Yield: a non-chemical analogy Billy comes home with his math test. He got 40 out of 75 questions right. Did he `pass’ the test ? Test Score = Test Yield = 100* 40 =53.3% 75

  13. Examples of chemical % yield 5O2 + C3H83CO2 + 4H2O Given mol excess 0.250.7(obs) Exp. Product mol 0.7 Theory product mol 4 x 0.25 =1 (theory=max)1 % yield =exp. mol x100 theory mol =0.7x 1001 = 70%

  14. Examples of chemical % yield (continued) 5O2 + C3H83CO2 + 4H2O MW 32 44 44 18 Given excess 1.1 g 0.5 g Exp. Mol CO2 = 0.5= 0.01136 44 Mol C3H8 = 1.1=0.025 44 Product CO2 moles theory = 3 x 0.025 =0.075 1 % yield = 100 * Exp Mol Theory Mol =0.01136 x 100% =15.1% 0.075

  15. Bob reports making 4.0 g H2O from 2.2 g C3H8. Is Bob crazy or okay ? Examples of chemical % yield (continued) 5O2 + C3H83CO2 + 4H2O MW 32 44 44 18 Bob Reports 4.0 g H2O Given excess 2.2 g Mol C3H8 =2.2 =0.050 44 Product H2O moles theory = 4 x 0.05 =0.2 mol 1 Maximum g H2O=18 g/mol*0.2 mol=3.6 g Bob’s an idiot

  16. MW 16 32 18 CH4 + 2O2 CO2 + 2H2OA 1 g sample of methane (CH4) is burned in excess O2 according to the equation above. You collect 1.125 g of H2O. What is your % yield ? • 50% • 89 % • 25 % • 100% • I have no idea

  17. Need more practice ????

  18. Where we are on the mole road trip…. We is done with moles !!!

  19. And now, after many weeks of &^%!! Moles ….for something completely different…. CLASSICAL REACTIONs

  20. Today’s Student Learning Objective (SLO): Students will be able to: write, balance, identify and predict common reaction classes (metatheses, acid-base,redox). SLO #6 Translation: What happens when I add this to that ?

  21. CLASSICAL REACTIONs (continued) What to read… chapter 4 ( + a bit of Ch. 14) • Metatheses 131-140 • Acid-base 140-147; 549-552 • Oxidation-reduction 147-159

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