14-6

**Percent Yield Lab** **//<---Previous Assignment - Next Assignment--->media type="custom" key="12468356"//** ** __Time Length__ ** ** __Instructions__ ** 1) read the following **Purpose:** to predict the amount of product generated from a double displacement reaction.
 * 1 Day

In class, you have learned how to use stoichiometry to determine the amount of a product generated from a chemical reaction. We call this the theoretical yield. In this lab, sodium bicarbonate (NaHCO3, a.k.a. baking soda) will be mixed with acetic acid (HC2H3O2, a.k.a. vinegar) to generate sodium acetate (NaC2H3O2) and carbonic acid (H2CO3). The carbonic acid will rapidly decompose to generate gaseous carbon dioxide and liquid water. You will calculate your theoretical yield of NaC2H3O2

For this reaction, we will need to use 0.025 moles of NaHCO3.

2) Make a new wiki titled 14-6 Percent Yield Lab (you can copy this worksheet to everyone else's wiki at the end.) 3) Calculate how many grams of sodium bicarbonate (NaHCO 3 ) you will need to measure out to obtain 0.025 moles. Record the quantity to measure out on your wiki. 2. Measure out the amount of NaHCO3 you calculated using a balance and a weighing paper. Attempt to get as close to your calculated amount as possible. Record this amount in your data table. 3. Weigh a clean 500 mL Erlenmeyer flask. Record this amount in your data table. 4. Dissolve the NaHCO3 in about 15 milliliters of distilled water in the 500 mL flask. Stir until it is mostly dissolved. (It is okay if some remains undissolved.) <span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">5. Obtain approximately 75 mL of acetic acid (a.k.a. vinegar) and **//__slowly__//** add it in small quantities to the flask containing the sodium bicarbonate solution. Wait for the bubbling to subside between additions so that the reaction does not overflow the flask. <span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">6. When all the acetic acid has been added, swirl flask or stir for two minutes with a glass stirring rod. <span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">7. When the solution is completely calm, move the flask to a hot plate and heat it to boiling. Be careful that the flask does not overflow, as this will hurt your calculations. <span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">8. When all the liquid has boiled away, remove the flask from the hotplate and allow it to cool to room temperature. <span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">9. When the flask has completely cooled, weigh it and record the mass in your data table. The salt in your flask is sodium acetate (NaC2H3O2), the product of the reaction. <span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">10. After weighing, clean your flask and any other glassware you used **//thoroughly//** and return it to the prep table. All waste can be washed down the sink.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">**Safety:** Boiling liquids, hotplates, and hot glassware can burn; take care. Wear goggles and apron.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">**Data:** create a data table using the procedure as your guide. It should have three entries.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">**Questions:** <span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">**Remember that all problem solving should be completed in your lab book.**

<span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">1. Write the balanced chemical equation for this reaction. (See introduction for reactants and products.)

<span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">2. Use the exact weight of the NaHCO3 that you weighed out and calculate the theoretical yield of NaC2H3O2 using a stoichiometric equation.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">3. Calculate the actual yield of NaC2H3O2 by using the weight of the empty flask and the weight of the flask after the reaction.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">4. Using the actual yield of NaC2H3O2 from # 3 and theoretical yield from #2, calculate the percent yield of NaC2H3O2 recovered in this lab.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">5. Was your percent yield of NaC2H3O2 100%? What factors might have caused any error you found? Explain, citing specific examples.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">6. Do you think it is common for scientists to get 100% yields? Why or why not?

<span style="font-family: 'Times New Roman',Times,serif; font-size: 140%;">7. If you had to do this lab again, what would you do differently to improve your results? Explain, using specific examples.