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:

Percent Yield Lab

Objective(s):

The objective of this lab is to examine the reaction between magnesium metal and oxygen gas.

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:

1.Select and weigh a clean, dry crucible to find the mass of the crucible and lid.

2.Record the mass of the empty crucible and lid in your data table.

3.Cut a small piece of metal from the magnesium ribbon.

4.With wool, remove the oxidized magnesium.

5.Roll the magnesium strip into a loose coil and place it inside the crucible.

6.Weigh the mass of the crucible, lid and magnesium inside.

7. Record the mass of the crucible, lid and magnesium inside.

8. Place the cubical with the magnesium inside on the burner for 10 minutes.

9. Turn off the burner and wait 5 minutes.

10. Weigh the cubical again and record the data.

Controlled variables: scale, heating time

            These are the controlled variables because they do not change throughout the experiment.

Independent variable: size of magnesium strip

This is the independent variable because it is the factor being changed in the experiment.

Dependent variable: weight

             This is the dependent variable because it is the factor that is the result of the change in the experiment.

Data:

Type the data in the data table below. Don’t forget to record measurements with the correct number of significant figures.

Data Trial 1 Trial 2
Mass of empty crucible with lid 26.698 g 26.687 g
Mass of Mg metal, crucible, and lid 27.060 g 27.046 g
Mass of MgO, crucible, and lid 27.291 g 27.273 g

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.

2 MG(s) + O2(g) = 2 MGO(s)

2.         Calculate the mass of magnesium metal used in each trial.

  1. Trial 1: .362 g
  2. Trial 2: .359 g

3.         Calculate the actual yield of magnesium oxide for each trial.

  1. Trial 1: .593 g
  2. Trial 2: .586 g

4.         Magnesium is the limiting reactant in this experiment. Calculate the theoretical yield of MgO for each trial.

  1. Trial 1: .6 g
  2. Trial 2: .596 g

5.         Determine the percent yield of MgO for your experiment for each trial. 

  1. Trial 1: 98.8%
  2. Trial 2: 98.3%

6.         Determine the average percent yield of MgO for the two trials.

  • 98.55%

Questions and Conclusions:

  1. Describe the process that was used in this lab to create magnesium oxide, specifically identifying the type of chemical reaction. Explain why the product had a higher mass than the reactant, and how this relates to conservation of matter.

Mg is weighed in a crucible and then heated to create a reaction with O₂ to produce MgO. This is an oxidation reaction because the magnesium gained O and oxidized to create MgO. The reason that the product had a higher mass than the reactant is because Mg bonded to O to form MgO, so the product had a higher mass because of the gain of an O atom. This relates to the conversation of matter because the law of conversation of matter states that the matter goes not destroyed or created from nothing, but it can convert from one form to other.

  1. 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.

During the step where the Mg strip is brushed with the wool, depending on the thickness of the strip and how much it is brushed, could have led to errors in measurement and weighing.

  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.

This process could reduce errors because it would provide a more reliable measurement of weight.

  1. 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.

My recommendation to the company would be to use lower costing materials and purchase more in order to increase production and yield. This is supported by the information in my lab because the average percent yield increased when more Mg was added.

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