What You Will Learn Theoretical, Actual & Percent Yield Why Is It Important? Actual results are more important than theoretical. Final Exam Theoretical, Actual & Percent Yield Theoretical yield The theoretical yield of a reaction is the amount of product that would be formed if the reaction went to completion. Actual yield Amount of a specified pure product actually obtained from a given reaction. Calculating Percent Yield Stoichiometry The left side and right side of the chemical reaction must have equal amounts of each element. We fix the problem by adding prefixes or coefficients. Stoichiometry After adding prefixes to the O2 and the H2O count the atoms on the left and right again. Are they equal now? Practice Calculating Theoretical Yield Determine the theoretical yield of hydrogen gas (H2) in grams for each of the following chemical reactions. 1. Zn + 2 HCl → ZnCl2 + H2 2. 2 H2O → 2 H2 + O2 3. Mg + 2 H2O → Mg(OH)2 + H2 Practice Calculating Percent Yield Determine the percent yield for the following reactions if the actual yield of hydrogen gas (H2) is 1 gram. 1. Zn + 2 HCl → ZnCl2 + H2 2. 2 H2O → 2 H2 + O2 3. Mg + 2 H2O → Mg(OH)2 + H2 Bell-Ringer: Theoretical Yield If your cell phone comes out you get a zero. Work alone & quietly. Open notebook – Part 1 of 4 (10 Minutes) Answer in your bell-ringer notebook in complete sentences. Determine the grams needed for each theoretical reaction. Example: 2MgO 80.6 grams 2Mg 48.6 grams + O2 32.0 grams Note the total mass before and after the reaction. 1. 8 Fe + S8 → 8 FeS 2. Zn + 2 HCl → ZnCl2 + H2 3. 2 H2O → 2 H2 + O2 4. HCl + NaOH H2O + NaCl Excess & Limiting Reactants What are the excess reactants? What are the limiting reactants? For limiting and excess we are talking about reactants. Bell-Ringer: Limiting Reagent If your cell phone comes out you get a zero. Work alone & quietly. Open notebook – Part 2 of 4 (10 Minutes) Answer in your bell-ringer notebook in complete sentences. Determine the limiting reagent in the following reactions. 5. 2C2H2 + 5O2 4CO2 + 2H2O Theoretical: _______ Actual: 52 grams 6. _________ 150 grams HCl + NaOH H2O + NaCl Theoretical: _______ Actual: 33.5 grams 7. Zn _________ 40 grams + 2 HCl → ZnCl2 + H2 Theoretical: _______ Actual: 65 grams 8. 8 Fe Theoretical: _______ Actual: 448 grams _________ 70 grams + S8 → 8 FeS _________ 251 grams Theoretical Yield For yield we are talking about products. Bell-Ringer: Percent Yield If your cell phone comes out you get a zero. Work alone & quietly. Open notebook – Part 3 of 4 (5 Minutes) Answer in your bell-ringer notebook. Determine the theoretical yield for each product. 9. 2C2H2 + 5O2 4CO2 + 2H2O 10. HCl + NaOH H2O + NaCl Bell-Ringer: Percent Yield If your cell phone comes out you get a zero. Work alone & quietly. Open notebook – Part 4 of 4 (5 Minutes) Answer in your bell-ringer notebook. Determine the percent yield for the given actual yield. 11. 2C2H2 + 5O2 4CO2 + 160 grams 12. HCl + NaOH H2O 15.5 grams 2H2O 34 grams + NaCl 45 grams Estimating Percent Yield Consider the following theoretical yield: Estimating Percent Yield Can we estimate how much product was actually made? Estimating Percent Yield Can we estimate how much product was actually made? A. 5% B. 10% C. 50% D. 100% Estimating Percent Yield Consider the following theoretical yield: Estimating Percent Yield Can we estimate how much product was actually made? Estimating Percent Yield Can we estimate how much product was actually made? A. 10% B. 30% C. 90% D. 100% Chemistry Humor or College Reality? Practical: MgSO4 + H2O MgSO4(aq) Working in pairs: 1. Record the weight of two plastic cups, one at a time. 2. Weigh approximately 10 grams of epsom salt into one plastic cup & record the exact grams. 3. Weigh approximately 50 grams of water into a different plastic cup & record the exact grams. 4. Calculate from this data what your theoretical yield of saltwater should be. 5. Now, make saltwater by repeatedly combining (pouring) the water and salt back and forth at least 10 times. 6. Weigh the finished product of saltwater & record the exact grams. 7. Calculate your percent yield of saltwater. Practical: Results: 1st MgSO4 + H2O MgSO4(aq) Practical: Results: 2nd MgSO4 + H2O MgSO4(aq) Practical: Results: 4th MgSO4 + H2O MgSO4(aq) Practical: Extra Credit After calculating the percent yield for your reaction, then calculate how many moles of MgSO4 were used in the following reaction… MgSO4 + H2O MgSO4(aq) 50 grams 50 grams of MgSO4 is equal to how many moles of MgSO4? Exit-Ticket: Percent Yield If your cell phone comes out you get a zero. Work alone & quietly. Open notebook – Part 1 of 1 (10 Minutes) Answer in your bell-ringer notebook in complete sentences. Calculate the percent yield for the following reactions. 1. 2C2H2 + 5O2 4CO2 + Theoretical: _______ Actual: 100 grams 2. HCl + NaOH + 2 HCl → + S8 _________ 30 grams ZnCl2 + Theoretical: _______ Actual: 100 grams 4. 8 Fe _________ 15 grams H2O + NaCl Theoretical: _______ Actual: 13 grams 3. Zn 2H2O → 8 FeS Theoretical: _______ Actual: 500 grams H2 _________ 2 grams
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