Stoichiometry Lab: The Determination of the Mass of Product of a Chemical Reaction Name ______________________________________Period _____ Objective: Use grams of CaCO3 and a balanced chemical equation to predict and then verify the grams of CaCl2 produced. Brief Overview: We will react calcium carbonate with an excess of hydrochloric acid. Write the Molecular Equation with Phases for This Reaction: A careful measurement of the mass of CaCl2 and knowledge of the balanced equation you wrote above will allow you to calculate the mass of CaCl2 expected to be produced. You can do this by using stoichiometry calculations! You will perform the reaction above in the lab and produce CaCl2 and then compare the expected amount of CaCl2 you found in your calculations with the amount you will actually produce in lab. Safety: 1) Make sure to wear goggles during the entire course of the lab, which includes all clean‐up time. 2) This lab involves handling glassware, which is breakable. Handle all glass with proper care, making sure not to drop or knock over any pieces. Also, be well aware of the position of the Bunsen burner and flame in this lab! 3) This lab also involves handling hydrochloric acid which is caustic and will destroy body tissues, especially the eyes. Be careful to avoid spills, splatter, or inhalation of vapor. 4) If you spill any acid, inform the teacher immediately! Materials: 150 mL beaker, graduated cylinder, pipette, electronic balance, ring stand, iron ring, wire gauze, Bunsen burner, solid calcium carbonate, and 3.00 M hydrochloric acid Procedures Preliminary Steps 1. Look over the following steps and discuss the procedure with your partner. Highlight the most important parts of the procedure. 2. Turn on the balance and make sure the reading shows 0.00. (Tare if needed) 3. Place an empty 150 mL beaker on the balance and record the mass in your data table. Then, press the tare button. The balance should reset to 0.00. 4. Add 2.00 grams of calcium carbonate to the beaker. 5. Pour 20.0 mL of 3.00‐molar hydrochloric acid into a graduated cylinder (make sure you use the correct number of sig figs which is dependent upon the precision of the grad cylinder…make your partner check this value!). 6. Using a pipette, add 3 drops of acid to the calcium carbonate in the beaker, moving the dropper so that no drops land on each other. The goal is to spread out the acid and to confine all splatter within the walls of the beaker. 7. Continue to add acid slowly to the beaker drop by drop. As liquid begins to build up, gently swirl the beaker. This is done to make sure unreacted acid reaches unreacted calcium carbonate. Do not add acid while swirling. 8. Your goal is to stop adding acid just when all bubbling has ceased! You are adding the minimum amount of HCl that will react with all of the calcium carbonate. When you think all bubbling has ceased, swirl the beaker and check for more bubbling. Add one drop more of acid and swirl. If no bubbling occurs, you are done. DO NOT ADD MORE ACID. 9. Measure the exact amount of HCl remaining in the graduated cylinder (make sure you are using consistent sig figs) and record the volume in the data table. Heating Procedure 1. Set up the ring stand, iron ring, wire gauze, and your Bunsen burner. The ring should be about 25 cm (10 inches) above the base of the stand. 1 Stoichiometry Lab: The Determination of the Mass of Product of a Chemical Reaction 2. Using your Bunsen burner, gently heat the beaker and its contents until all the liquid is driven off leaving behind the solid. Allow the beaker to cool on the stand for about 2 minutes, then use the beaker tongs to transfer to your lab bench for a minute to continue to cool (you cannot place a hot beaker on the balance)! (This would be a good time to begin calculations.) 3. Weigh the beaker and its contents (“first weighing”) and record in the data table. 4. Gently reheat the contents of the beaker using the same procedure (#2) for approximately three minutes. Then allow the beaker to cool for the same duration as in #2. (Continue your calculations during the wait.) 5. Weigh the beaker and its contents (“second weighing”) and place this in the data table. 6. If your two weights are consistent (within 0.05 grams), you may move on to the next steps. If not, perform a third heating for a third weighing. Clean‐Up Steps 1. Pour any remaining HCl solution down the drain with the water running. 2. Thoroughly rinse the graduated cylinder and plastic pipette with tap water (TRIPLE RINSE). 3. Thoroughly rinse the beaker that contained the CaCl2 with tap water(TRIPLE RINSE). 4. Put all glassware on some paper towels to dry. 5. Make sure you have all the data. Do not depend on your partner to solve all the problems. Every person should be able to explain and perform all calculations 6. Make sure you wash your hands! Data Table Title: _________________________________________________________________________ Prior to Heating After Heating Mass Grams Mass Grams Empty Beaker CaCl2 + Beaker (first weighing) CaCO3 CaCl2 + Beaker after heating (second weighing) CaCl2 + Beaker after heating (third weighing if needed) Volume of HCl before reacting Volume of HCl after reacting Rewrite the Molecular Equation that represents the reaction that occurred in this lab: Data Analysis: (You must number each of the following calculations and clearly show all in your lab notebook! Numbers without correct units will not receive credit!) Write the grams of CaCO3 you had in your beaker at the beginning of this experiment: __________ 1. Calculate the number of moles of CaCO3 in the mass sample above. 2. Calculate the number of moles of CaCl2 you predict would be produced in your experiment. This involves using the stoichiometry calculations we’ve been doing in class! Be sure to show all work including units. 2 Stoichiometry Lab: The Determination of the Mass of Product of a Chemical Reaction 3. Calculate the mass of CaCl2 you predicted would be produced in this lab. 4. You did not weigh the HCl. However, based on your calculations above, determine the mass of HCl theoretically used to react with the mass of CaCl2. 5. You did not use all of the 20mL of acid. This means you had excess acid. In stoichiometry, we call this the excess reactant. We had too much of this reactant compared to the amount of the other reactant (CaCO3). Because we did not have enough CaCO3 to react with all the acid, we call CaCO3 the limiting reactant. What volume of acid did you have in excess? 6. What was the purpose of heating the CaCl2 solution in this experiment? Be specific. 7. Determine the actual mass of CaCl2 produced in your experiment. Make sure you show all of your work! a. First Weighing of CaCl2: _________________ b. Second Weighing of CaCl2: _______________ Mass of CaCl2_______ c. Third Weighing of CaCl2:(if needed) _________________ 8. Using the theoretical value of CaCl2 produced (which you found by using the stoichiometry calculation in #3); calculate the percent yield of CaCl2. [#9 and #10 will appear in the conclusion section…Error Analysis] 9. What are some plausible reasons why the percent yield could be less than 100%? In your answer, show exactly how the reasons you explained would affect specific calculation results. 3 Stoichiometry Lab: The Determination of the Mass of Product of a Chemical Reaction 10. What are some plausible reasons why your percent yield could be more than 100%? In your answer, show how the reasons you explained would affect specific calculation results. 11. Determine the theoretical amount of water produced from the reaction you did in lab. Be sure to show all work including units! 12. Could you determine the percent yield of water produced in this lab? Explain why or why not. 13. The concentration of HCl we used in this lab was 3.00M. The M stands for molarity which is found from using the equation: M= moles. L a. Using this information, determine the moles of HCl used in this lab to react with CaCO3. [Simply set up a dimensional analysis problem and use the value and units of CaCO3 to cancel until you get moles of HCl.] b. Determine the theoretical volume of HCl need to react with the mass of CaCO3 used in this lab. Remember that you find theoretical amounts by using stoichiometric calculations. c. Could you determine the amount of excess grams of HCl left over after the reaction was completed? Examine your answers to questions 4 and 5 above for this analysis. Show all work for this answer. 4