Tues 9-22 and Wed 9-23 Percent Yield and Stoichiometry Lab Mrs. Wilson

Objectives 1. Use stoichiometry and percent yield to predict and produce a mass of product from a chemical reaction. 2. Practice lab safety procedures. 3. Follow lab directions and reduce determinate error. Homework: Study for Major Quiz 1-12 next class (Moles, Mole Conversions, Stoichiometry and Percent Yield)

Example of a Stoichiometry Calculation Ca(OH)2 (s) + 2 HCl (aq) → CaCl2 (aq) + H2O (l) If 82.31 g of HCl react with sufficient Ca(OH)2, what is the expected number of moles of CaCl2 that we should produce?

Daily Quiz 1-11 Feel free to use a calculator and a periodic table. Obtain a golden daily quiz sheet. Show all of your work neatly and in a logical order. Use sig fig rounding rules and an appropriate unit after your final answer. Do not return the calculator or periodic table after the quiz.

Chemistry Quiz 1.2 Properties of Matter Analysis Look at your returned quiz. Write down the number of questions you got correct for each category. This will help you understand what material you need to review and master before the Unit 1 Exam next week. I can take a few brief questions over the quiz in class today – please feel free to email me or see me in office hours if you want a one-on-one review. Turn to Lesson 1.10 in your packet when you are done.

Percent Yield % Yield = actual yield x 100% theoretical yield Side reactions, determinate errors, etc. can LOWER the amount of product that is really made. Theoretical yield is the mass of product you PREDICT, based on calculation. The actual yield is the amount of product you REALLY make. % Yield = a comparison of actual yield to theoretical yield. (The higher the percent yield, the more precise your experimental results are.) % Yield = actual yield x 100% theoretical yield

Example of a Percent Yield Calculation 2 Na (s) + Cl2 (g)  2 NaCl (s) You calculate that reacting 25.00 g of Na with sufficient Cl2 will yield 63.55 g of NaCl. After the experiment, you recover only 49.72 g of NaCl. What is the percent yield of your experiment?

Stoichiometry Lab – General Guidelines 1. Please follow lab safety rules, including goggles, closed toe shoes and tying hair back. 2. Please put all bags at the front. 3. Please read and follow the lab procedure very carefully. 4. Hot glass looks like cool glass! 5. Note the chemical equation for question #1.

Stoichiometry Lab – General Guidelines 5. While you are waiting for glass to cool, work on the Stoichiometry Practice Problems. The flame should be turned OFF. Answers will be shown so you can check your work. 6. Turn the burner flame off right after you are finished heating. 7. I will stand by the balances for the “official weigh-in.” Bring your papers to me and a calculator so I can give you your “grade” for question #4. 8. After gathering all your data, clean up, wash and dry the cool test tube, throw out the used swabs, and begin calculations. The lab rubric is on today’s blog post – PLEASE read it! You MUST get the FRONT HALF of the lab handout done TODAY.

How to Light a Bunsen Burner Start at 0.25

Stoichiometry Practice Problems - ANSWERS Br2 + 2 NaI  2 NaBr + I2 2. 3.00 moles 3. 3.00 x 103 grams 4. 79.4 g 5. 35.4 g 2 H2 + O2  2 H2O 6. 5.00 moles 7. 57.6 g 2 KClO3  2 KCl + 3 O2 8. 576.0 g 9. 498 moles  

Exit Ticket What did you learn today about stoichiometry? Describe what you learned.