Chem 1025 Stoichiometry
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Stoichiometry Lab INTRODUCTION A balanced equation, like a recipe, should allow us to predict how much product we are able to collect. The relationship between substances in a balanced chemical equation is called stoichiometry. In this lab we are going to look at a very simple reaction, with a very predictable amount of product, or “theoretical yield.” In a reaction involving more than one substance reacting, we may find that one substance controls the amount of product, and this is because it is largely consumed before the other. This substance is termed the limiting reactant. When it is gone from the reaction mixture, no more product may be made and the reaction stops. Even if we continue to add more of the other reactants, there can still be no reaction. The reacting substances that are not consumed are said to be “in excess”. In our reaction, we are able to compare the amount of product that we are creating because it is a gas. We will collect the gas produced and attempt to compare the yields, based on the conditions. In lab, as in life, however, the data is not usually as good as what we expect. As you perform the experiment, look for reasons that the amount of gas may not be an accurate reflection of the reaction, As always, when mixing materials, especially when gases are involved, you will want to wear adequate PPE. Prepare your notebook. When the lab is complete your lab notebook should include the following:

1. Include Stoichiometry Lab in the Table of Contents 2. Write the title of the lab on the top of the page. 3. Date/number the page (if you work on it over a few days, date each time you are

working). Sign in your lab notebook each time you stop working. 4. Record the Purpose of Experiment in your own words. Remember the purpose is the

overall question that will be answered by collecting the data and doing any requested calculations.

5. Indicate PPE (personal protection equipment) required while performing the lab: goggles, gloves, lab apron, and closed-toed shoes.

6. Prepare your notebook to record observations. 7. Complete the post-lab question.

Stoichiometry Activity: In this lab we will study limiting reactants, excess reactants and calculations from a balanced chemical equation. We will also be looking for errors that occur while performing the reaction. Materials/Equipment needed: Lab kit bag L05 20 oz (around 600mL) water bottle or soda bottle, rinsed out 100 mL graduated cylinder

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Purpose: To make carbon dioxide from NaHCO3 and HC2H3O2 and to calculate the theoretical yield and limiting reagent for each. Procedure: In this experiment you will 1) Label the packets of NaHCO3 in your lab kit bag: Experiment 1, Experiment 2,

Experiment 3. Record the masses on each labeled packet of NaHCO3 in your Data Table 1 in the respective boxes. Each packet is for a different trial for the same reaction.

2) Record the volumes used for each trial in the Data Table 1. a. Experiment 1: 25.0 mL water, 25.0 mL vinegar (0.55M acetic acid) b. Experiment 2: 20.0 mL water, 30.0 mL vinegar (0.55M acetic acid) c. Experiment 3: 30.0 mL water, 20.0 mL vinegar (0.55M acetic acid)

3) Experiment 1: Empty Packet 1 into your empty water bottle. Use your graduated cylinder to measure the volumes of your liquids. Add 25 mL water and swirl to dissolve the solid. Add 25 mL of the vinegar. Cover the water bottle with a balloon and swirl the bottle while holding the balloon in place. When it stops expanding, remove the balloon and seal it. Rinse out the bottle down the sink. Mark the balloon with the experiment number 1.

4) Experiment 2: Repeat the process using the packet for trial 2. This time using 20 mL of water 30 mL of the vinegar. Mark the balloon with the experiment number 2

5) Experiment 3: Repeat the process using the packet for trial 3. This time using 30 mL water and 20 mL of the vinegar. Mark the balloon with the experiment number 3

6) Compare the balloons. Order the trials be the size of the balloon from smallest (1) to largest (3). Record the order in Data Table 1. Take a picture of the balloons and upload with your lab.

Data Table 1

Experiment 1 Experiment 2 Experiment 3

Mass NaHCO3 (g)

Volume H2O (mL)

Volume 3% (0.55M) acetic acid (mL)

Ranking of Collected Gas Volume (1-3, 1 being smallest)

Processing your data Sample Calculations: For your sample calculations, show your work below for the first set of data collected. Record all results in your summary of intermediate calculations

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1) Calculate the moles of NaHCO3 in your first packet. 2) The density of white vinegar(0.55M acetic acid) is 1.106 g/mL. Using the density and

the volume, of vinegar that you used, determine the mass of vinegar that you used for each trial.

3) Now, using the mass of vinegar, and knowing that the concentration of white vinegar is on the order of 3% by mass, find the mass of acetic acid in the vinegar for each trial.

4) Using the mass of acetic acid calculate the moles of acetic acid. The expected reaction was NaHCO3+HC2H3O2 à H2O(g)+NaC2H3O2+CO2(g) 5) What is the expected number of moles of carbon dioxide based on the amount of

NaHCO3 used? 6) Based on the moles of acetic acid, what is the expected yield, in moles of carbon dioxide. 7) Which reagent is the limiting reagent? Explain how you know. The limiting reagent tells

us the expected yield of carbon dioxide. 8) Finally, if we expect that there are 24.4 L = 1 mol of gas at room temp, what volume of

CO2 should we have observed in each trial? Summary of intermediate calculation results:

Experiment 1 Experiment 2 Experiment 3

Mole NaHCO3

Mass of vinegar used (g)

Mass of acetic acid in vinegar sample (g)

Moles of acetic acid used (mol)

Yield CO2 expected from amount of sodium bicarbonate (mol)

Yield CO2 expected from amount of acetic acid (mol)

Theoretical Yield of CO2 (mol)

Theoretical Yield of CO2 (mL)

Expected Rank in Volume of gas collected (1-3, where 1 is the lowest amount)

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Conclusion: Did your observations match your expectations? Explain why or why not. Think about the mL of CO2 predicted compared to the ranking of your balloon volumes. Be specific and include sources of error and the effect of the error on your yield of CO2(g). Post-lab Problems The problems are based on the following equation: Na2CO3(s) + 2 HCl(aq) ® 2 NaCl(s) + H2O(g) + CO2(g) 1) Calculate the mass (in grams) of NaCl produced by the reaction of 7.53 g Na2CO3 with an

excess of concentrated (12.1M) HCl. 2) Determine the grams of water produced if 23.4 g of HCl is allowed to react with excess

Na2CO3? Works cited: Mullins, N.J., & Milczanowski, S.E. (2020). Lab Manual for Introductory Chemistry CHM1025C/CHM 1032C. Jacksonville: FSCJ Copy Center