5.06 chem lab

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CHM2046

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Chemistry

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Feb 20, 2024

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Percent Yield Lab Report Instructions: For this investigative phenomenon, you will need to determine the percent yield of magnesium oxide from the given reaction to determine if it is a useful commercial process. Record your data and calculations in the lab report below. You will submit your completed report. Title: Determining Percent Yield Objective(s): -Learn how to determine percent yield of a chemical reaction. -Learn how to use percent yield to find the actual yield of a chemical reaction Hypothesis: No hypothesis needed for this lab. Your theoretical yield calculation serves as your prediction for what you expect the lab to produce, and that will be determined later in the lab. Procedure: Access the virtual lab. Because this lab is virtual, summarize the steps used to collect your data. In addition, list and explain your controlled variables, independent variable, and dependent variable for this lab. Materials: Percent Yield Virtual Lab Variables: Remember, controlled variables are factors that remain the same throughout the experiment. An independent (test) variable changes so that the experimenter can see the effect on other variables. The dependent (outcome) variable will change in response to the test variable. Controlled variables: Ring stand, steel wool, magnesium metal ribbon, Bunsen burner, and a crucible. Independent Variable: size of the magnesium strip

Dependent Variable: weight Summary of Steps: 1. Weigh a clean crucible in order to find its mass. 2. Record the mass in a table. 3. Cut a small piece of metal from the magnesium ribbon. 4. Utilize the steel wool in order to remove oxidized magnesium. 5. Put the magnesium strip in the crucible after rolling it into a coil. 6. Weigh the magnesium, crucible, and lid of the crucible. 7. Record the mass found in step 6. 8. Put the crucible and magnesium onto the Bunsen burner for 10 minutes in order to heat them. 9. After the 10 minutes pass, allow the crucible and magnesium to cool for a few minutes, 10. Weigh it once more. 11. Record the mass found in step 10. Data: Type the data in the data table below. Don’t forget to record measurements with the correct number of significant figures. Hint: Using the same instrument, you should have the same number of digits to the right of the decimal. Data Trial 1 Trial 2 Mass of empty crucible with lid 26.693 g 26.674 Mass of Mg metal, crucible, and lid 27.146 g 27.098 Mass of MgO, crucible, and lid 27.281 27.198 Calculations: Show your calculations for each of the following . Remember, calculations should follow rules for significant figures. 1. Write the balanced chemical equation for the reaction you are performing. Mg + O2  MgO 2Mg + O2  2MgO

2. Subtract the mass of the crucible and lid (row 1 in the chart) from the total mass of Mg, crucible, and lid (row 2 in the chart) to find the mass of magnesium for each trial.  Trial 1: 27.281 - 27.146 = 0.135  Trial 2: 27.198 – 27.098 = 0.1 3. Subtract the mass of the crucible and lid (row 1 in the chart) from the total mass of MgO, crucible, and lid (row 3 in the chart) to find the mass of magnesium oxide for each trial. This is the actual yield of magnesium oxide for each trial.  Trial 1: 27.281 – 26.693 = 0.588  Trial 2: 27.198 – 26.674 = 0.524 4. Magnesium is the limiting reactant in this experiment. Calculate the theoretical yield of MgO for each trial.  Trial 1: 27.146 - 26.693 = 0.453 24 g of Mg = 80 g of MgO 0.453 of Mg = x g of MgO X g of MgO = 0.453 x 80/24 X g of MgO = 1.51 g  Trial 2: 27.098 - 26.674 = 0.424 24 g of Mg = 80 g of MgO 0.424 g of Mg = x g of MgO X g of MgO = 0.424 g x 80/24 X g of MgO = 1.413 g 5. Determine the percent yield of MgO for your experiment for each trial.  Trial 1: 27.281- 26.693 = 0.588 Percent yield = actual yield/theoretical yield x 100 0.588 g/1.51 g x 100 38.94%  Trial 2: 27.198 – 26.674 = 0.524 0.524 g/1.413 g x 100 37.08% 6. Determine the average percent yield of MgO for the two trials. 38.94 + 37.08 = 76.02/2 = 38.01% Conclusion: Write a conclusion statement that addresses the following questions:

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 Explain why the product had a higher mass than the reactant, and how this relates to conservation of matter. -The product had a greater mass than the reactant because Mg bonded to O, which formed MgO. The gain of an O atom increased the mass of the product. This related to the law of conservation of matter, which states that matter cannot be destroyed or created, however it can be converted from one form to another. In this case, Mg and O combine, causing their two respective masses to convert into one.  What sources of error may have contributed to the percent yield not being 100 percent? (Think about things that may have led to inaccurate measurements or where mass of the product could have been lost if this experiment was conducted in a physical laboratory.) Inaccurate measurements could have happened when the Mg strip is brushed with wool, depending on how much it is brushed.  How do you think the investigation can be explored further? The investigation could be further explored by performing additional trials or repeating the experiment utilizing different elements. Post-Lab Reflection Questions Answer the reflection questions using what you have learned from the lesson and your experimental data. It will be helpful to refer to your chemistry journal notes. Answer questions in complete sentences. 1. When conducting this experiment, some procedures call for heating the substance several times and recording the mass after each heating, continuing until the mass values are constant. Explain the purpose of this process and how it might reduce errors. The purpose of this process is to demonstrate consistency between both the mass of the magnesium and magnesium oxide. This reduces errors by assuring reliability. 2. Your company currently uses a process with a similar cost of materials that has an average percent yield of 91 percent. If the average percent yield of this process is higher than that, this could save the company money. What is your recommendation to the company? Please support your recommendation using your data, calculations, and understanding of stoichiometry gathered from this lab. I would recommend that the company should attempt a different method. Their process results in a lower percent yield compared to the technique used in the experiment described above. It is also a simple method that does not require skill.