Stoichiometry Lab Introduction: A Balanced Equation ✓ Solved

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Stoichiometry Lab INTRODUCTION A balanced equation, like a r

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: Include Stoichiometry Lab in the Table of Contents. Write the title of the lab on the top of the page. 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. 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. Indicate PPE (personal protection equipment) required while performing the lab: goggles, gloves, lab apron, and closed-toed shoes. Prepare your notebook to record observations. Complete the post-lab question.

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
• 20 oz (around 600mL) water bottle or soda bottle, rinsed out
• 100 mL graduated cylinder

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.
   • Experiment 1: 25.0 mL water, 25.0 mL vinegar (0.55M acetic acid)
   • Experiment 2: 20.0 mL water, 30.0 mL vinegar (0.55M acetic acid)
   • 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 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 and 30 mL of 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 vinegar. Mark the balloon with the experiment number 3.
6. Compare the balloons. Order the trials by 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 it with your lab.

Data Table 1:

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.

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.
5. The expected reaction was NaHCO3 + HC2H3O2 → H2O(g) + NaC2H3O2 + CO2(g).
6. What is the expected number of moles of carbon dioxide based on the amount of NaHCO3 used?
7. Based on the moles of acetic acid, what is the expected yield, in moles, of carbon dioxide?
8. Which reagent is the limiting reagent? Explain how you know. The limiting reagent tells us the expected yield of carbon dioxide.
9. 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:

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.

Paper For Above Instructions

The Stoichiometry Lab introduces students to fundamental concepts in chemistry such as balanced equations and the laws of conservation of mass and energy. Through the experiment, students create carbon dioxide from sodium bicarbonate (NaHCO3) and acetic acid (HC2H3O2), allowing them to engage with the theoretical yield and limiting reagents in a hands-on way. Understanding these concepts is crucial for any aspiring chemist and will aid in connecting abstract chemistry concepts with practical experiments.

The theoretical yield is the maximum amount of product that could be formed from given quantities of reactants, based on stoichiometric calculations. In our experiment, we utilize the reaction:

NaHCO3 + HC2H3O2 → H2O(g) + NaC2H3O2 + CO2(g)

This balanced equation helps us determine the amount of carbon dioxide produced by measuring the initial mass of NaHCO3 and the volume of acetic acid used in each trial. During the experiment, it is critical to identify the limiting reactant, which is the substance that is fully consumed first during the reaction, effectively halting further production of the product.

The procedure was divided into three distinct trials, each varying the volume of reactants. For instance, Experiment 1 used 25.0 mL of water and 25.0 mL of vinegar (0.55M), while Experiment 2 utilized 20.0 mL of water and 30.0 mL of vinegar, and lastly, Experiment 3 incorporated 30.0 mL of water with 20.0 mL of vinegar. The differences in volumes serve the purpose of identifying how varying reactant amounts affect the yield of carbon dioxide gas.

Data collection during each trial involved noting the mass of NaHCO3, measuring the produced gas, and ranking the results based on gas collection volume. This ranking provides a tangible way to assess the effectiveness of each reactive combination.

Upon analyzing the data and calculating the expected yields using stoichiometry, inconsistencies often arise due to various experimental factors. These may include the accuracy of measurement, gas leakage from the balloon, or incomplete reactions, emphasizing the importance of precision and careful methodology in experimental design.

A noteworthy part of the experiment involved calculating the moles of acetic acid in the vinegar used, which was 0.55M; this concentration helped to determine the corresponding moles of carbon dioxide expected from each trial. The mass calculations were critical to establishing the theoretical yield. For instance, using the density of vinegar, we convert volumes to mass, ultimately allowing for stoichiometric calculations between NaHCO3 and HC2H3O2.

For example, using 25.0 mL of acetic acid will yield approximately 0.055 moles of acetic acid (given the density and percentage concentration). Using this information, the expected moles of carbon dioxide can be calculated, allowing us to identify how many moles would be generated based on the limiting reactant. This experimental design provides an excellent opportunity for students to relate chemistry principles directly to observed phenomena.

In conclusion, as students performed the stoichiometry lab, they not only engaged with chemical reactions but also learned about the unpredictability and variability inherent in experimental science. By analyzing the balloons’ volume, students are encouraged to reflect on their findings versus their expectations, considering factors such as gas loss or discrepancies in measurements. Such reflections are essential in reinforcing learned principles and preparing students for future investigations in chemistry.

References

• Mullins, N.J., & Milczanowski, S.E. (2020). Lab Manual for Introductory Chemistry CHM1025C/CHM 1032C. Jacksonville: FSCJ Copy Center.
• Ebbing, D.D., & Gammon, S.D. (2016). General Chemistry. Cengage Learning.
• Wade, L.G. (2015). Organic Chemistry. Pearson.
• Atkins, P.W., & Jones, L. (2010). Chemical Principles: The Quest for Insight. W.H. Freeman and Company.
• Benz, M., & van Yperen, J. (2021). Exploring Chemistry Experiments and Techniques. Springer.
• Brown, T.L., LeMay, H.E., Bursten, B.E., & Murphy, C.J. (2018). Chemistry: The Central Science. Pearson.
• Petrucci, R.H., Harwood, W.S., & Herring, F.G. (2017). General Chemistry. Pearson.
• McQuarrie, D.A. (2008). Quantum Chemistry. University Science Books.
• Silberberg, M.S. (2016). Chemistry: The Molecular Nature of Matter and Change. McGraw-Hill.
• Rosenberg, P., & Gillis, J. (2019). Lab Safety: A Guide to Protecting Yourself in the Lab. Safety First Publishing.

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