General Chemistry

1. Faculty of Allied Medical Sciences General Chemistry (MGGC-101)

2. Limiting reagent, theoretical and percent yield Supervision: Prof.Dr.Shehata El-Sewedy Dr.Fatma Ahmed

3. Outcomes By the end of this lecture, the students will be able to 1-Understand the Limiting Reagent 2-learn to excess reactant of the reactions 3-To differentiate between theoretical and percentage yield 4-Recognize actual yield

4. Limiting Reagent • The limiting reagent (or limiting reactant): is the reactant which is completely consumed in the reaction. The other reactant will be in excess. For example

5. 2NO + 2O2 2NO2 Limiting Reagents NO is the limiting reagent O2 is the excess reagent 3.9

6. Example Zinc metal reacts with hydrochloric acid by the following reaction: Zn(s) + 2 HCl(aq)  ZnCl2(aq) + H2(g) If 0.30 mol Zn is added to hydrochloric acid containing 0.52 molHCl, how many moles of H2 are produced? Answer: Take each reactant and calculate how much product would be obtained if each were totally consumed. The reactant that gives the smaller amount is the limiting reagent. Zn  H2 1 mole I mole 0.30 mole X ?  X (no of moles of H2) = 0.30 mole. similarly: 2 HCl H2 2 mole I mole • 0.52 mole X ?  X (no of moles of H2) = 0.26 mole. Since HCl is the limiting reagent, the amount of H2 produced must be 0.26 mol. Zinc is the excess reactant.

7. Example 2SO2(g) + O2(g) + 2H2O(l) → 2H2SO4(aq) How much H2SO4 can be formed from 5 moles of SO2 and 2 moles O2 and unlimited quantity of H2O ? Answer SO2 : 2H2SO4 2 : 2 5 X mol 5 moles of SO2 will give 5 moles of H2SO4, while O2: H2SO4 1 : 2 2 X H2SO4formed = 4 moles 2 moles O2 will give 4 moles of H2SO4 .  O2 is the limiting reagent

8. Theoretical and Percent Yield • The theoretical yield of product is the maximum amount of product that can be obtained from given amounts of reactants. • The percentage yield is the actual yield (experimentally determined) expressed as a percentage of the theoretical yield (calculated).

9. Example 2C6H12 + 5O2 2H2C6H8O4 + 2H2O cyclohexane adipic acid Assume that the reaction start with 25gram cyclohexane which is the limiting reagent. a-What is the theoretical yield of adipic acid. b- If you obtain 33.5gram adipic acid calculate the % yield. Answer 2C6H12 2H2C6H8O4 2moles : 2 moles 2(mol. mass) 2(mol.mass) 2X 84 2X 146 25g X g Grams adipic acid = 2 146X25/2X84 = 43.45 grams. a- Theortical yield = 43.45gram. b- % yield = (33.5 / 43.45)  100 = 77.1%

10. Quiz time

11. Zinc metal reacts with hydrochloric acid by the following reaction: Zn(s) + 2 HCl(aq)  ZnCl2(aq) + H2(g) If 0.30 mol Zn is added to hydrochloric acid containing 0.52 molHCl, how many moles of H2 are produced? 2SO2(g) + O2(g) + 2H2O(l) → 2H2SO4(aq) How much H2SO4 can be formed from 5 moles of SO2 and 2 moles O2 and unlimited quantity of H2O ? 2C6H12+ 5O2 2H2C6H8O4 + 2H2O cyclohexane adipic acid Assume that the reaction start with 25gram cyclohexane which is the limiting reagent. a-What is the theoretical yield of adipic acid. b- If you obtain 33.5gram adipic acid calculate the % yield.

12. Student Question

13. Define Limiting Reagent Theoretical yield Percentage yield 2C6H12+ 5O2 2H2C6H8O4 + 2H2O cyclohexane adipic acid Assume that the reaction start with 25gram cyclohexane which is the limiting reagent. a-What is the theoretical yield of adipic acid. b- If you obtain 33.5gram adipic acid calculate the % yield.

14. Assignments(1)

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18. 1-Raymond Chang. Chemistry. 10th ed. 2009 2-Zumdehl. International edition. 2009 Recommended textbooks: