In this lab, students perform a reaction between acetic acid and sodium bicarbonate and determine the amount of product formed and the limiting reactant.
By the end of this lesson, students should be able to
- determine the limiting reactant in a reaction.
- calculate percent yield.
- calculate the mass of excess reactant left.
This lesson supports students’ understanding of
- Limiting reactants
- Percent yield
Teacher Preparation: 30 minutes
Lesson: 1 hour
For each group:
- Sodium bicarbonate
- Weight boat
- 5% vinegar solution
- 125-mL flask
- Glass stir rod
- pH paper
- Always wear safety goggles when handling chemicals in the lab.
- Students should wash their hands thoroughly before leaving the lab.
- When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
This lab is quite simple, but is very engaging for students.
For the Student
To identify the limiting reactant experimentally and to determine the percent yield of the product.
- Mass approximately 3 g of NaHCO3 and record the exact mass in your data table. Keep off to the side for later.
- Mass a balloon and record that mass in your data table.
- Measure approximately 30 mL of a 5% vinegar solution. Record the exact volume in your data table.
- Add the measured acetic acid to a 125-mL flask.
- Test the pH of the acid by dipping a glass stir rod into the solution and then touching it to a piece of pH paper. Record the pH in your data table. Save this paper for a later step.
- Carefully pour the sodium bicarbonate into a balloon using a funnel. Using the technique your teacher showed you, attach the balloon to the mouth of the flask. When you are ready to start the reaction, lift the balloon up so ALL the sodium bicarbonate drops into the flask. Swirl the flask to mix the chemicals until the reaction seems complete. Record observations.
- Remove the balloon and tie it up so that the gas inside is not lost. Zero a weigh boat on the balance and put your balloon in the weigh boat. Record this mass in your data table.
- Test the pH of the solution in the flask by dipping a glass stir rod into it and touching the pH paper used earlier. Record the pH in your data table.
- Pop balloon with a thumbtack to slowly let the gas out and throw it out. Rinse out your flask with water. Clean up the rest of your lab area.
|Before reaction took place||During the reaction||After the reaction|
|Mass of NaHCO3 (grams)|
|Initial mass of the balloon (grams)|
|Volume of vinegar (mL)|
|Mass of NaHCO3 (grams)|
Calculate the mass of HC2H3O2 in the vinegar solution by doing the following:
a. Vinegar contains 5% HC2H3O2 by volume. Find the volume of HC2H3O2 in the vinegar solution. Show your work.
b. Use the density of HC2H3O2, 1.05 g/mL, to calculate the mass of the acetic acid in your sample. Show your work. Record this mass in your data table.
- Write a balanced chemical equation for the reaction between acetic acid and the sodium bicarbonate. The products are aqueous sodium acetate, liquid water, and carbon dioxide gas.
- What evidence from the lab shows that a chemical reaction took place? Explain.
- Which product was collected in your balloon? Explain.
- According to the quantities you used of the two reactants and the amount of carbon dioxide you produced, which is the limiting reactant?
- Look at your observations. Was there any indication that this would be your limiting reactant based on your observations? Explain.
- What mass of the excess reactant was left unreacted?
- What is the theoretical yield of carbon dioxide?
- What is the actual yield of carbon dioxide?
- What is the % yield of product produced in this lab?
- Why was your % yield less than 100%? State one experimental error that could have occurred in the lab and how this contributed to your % yield.
- What was the point of taking the pH before and after the reaction? What did it tell you?
- What would you have to do in this lab for the balloon to get bigger? Explain why this would work.