Theoretical vs. Actual Yield

The reaction of calcium carbonate with hydrochloric acid to produce water, calcium chloride and carbon dioxide will be studied. The loss of mass due to the escape of carbon dioxide gas will be predicted based on the starting mass of calcium carbonate and the chemical equation:
CaCO3 + 2HCl --> H2O + CaCl2 +CO2
This prediction will be tested by comparing a measurement of the mass of the combined reactants before and after the reaction. The percent yield will be calculated and reasons for its failure to be 100% will be investigated.

1. 300 mL or 500 mL Erlenmeyer flask5. lab balance
2. approx. 35 g CaCO36. stirring rod
3. 150 mL 6 molar HCl7. lab notebook
4. a watch glass8. safety gear

Pre-Lab Questions
Write your answers to these questions neatly on a separate piece of paper, showing all steps of all calculations. Be sure to do the calculations before the experiment and to re-write them if they aren’t neat and easy to read.
  1. What is the molar mass of each reactant and product?
  2. What is the most important molar ratio this experiment will be concerned with?
  3. How many moles of calcium carbonate are represented by 35 g?
  4. One hundred fifty milliliters of six molar hydrochloric acid solution represents 0.9 mol (take my word for it). Which reactant is in excess? Which is the limiting reactant? By how much (in moles) does the excess reactant exceed the limiting reactant?
  5. Based on your answers to the previous question, how many moles of carbon dioxide do you expect the reaction to produce?
  6. How many grams is that?
  7. Say you measure a loss of only 7.5 g (meaning that 7.5 g of carbon dioxide escaped). What would the percent yield be? (Remember to convert to moles first!)
Safety Note: Six molar hydrochloric acid has six moles of acid per liter of solution. This is strong enough to cause serious burns and irritation of the skin. If contact with the skin is made immediately rinse with plenty of water and neutralize with baking soda, if possible.
Write a lab report on a separate piece of paper and be sure to create and include a neat, readable data table. Keep this lab for future reference. The lab report should include the following sections:
Abstract: Briefly (50 words or fewer) state the purpose and findings of the lab. Free advice (isn’t it always?): do not write the abstract until you have written the rest of the report and done all of your calculations since you need to report your results in the abstract, anyway.
Materials: Write a list of the materials used in the lab.
Procedure: Write the procedure given in your own words.
Data: You will collect two kinds of data: qualitative and quantitative. The qualitative data include your own impressions and observations about the experiment and may include pictures. The quantitative data are the data you were told to collect in the procedure. Also include any other numerical data that is relevant.
Data Analysis: Calculate the actual yield of carbon dioxide. Find the percent yield using the theoretical yield you calculated in the pre-lab questions. Show all work clearly.
Error Analysis: be sure to mention how possible errors may affect results. Do not simply say that ‘human error’ probably caused problems in the data. That is a given. Try to think of what could be changed in the experimental design to ensure better data. For instance, would a sample of calcium carbonate that was quite a bit finer have given better results? Why?
Conclusion: Briefly state your results. No new information should be introduced here.
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