Name: ______Period: ______

Stoichiometry through a Precipitation Reaction

Materials

Taken from Grapevine Colleyville ISD, SMG, Experiment 6

  • 0.0175 moles of Na2CO3
  • ______g Na2CO3
  • 0.0125 moles of CaCl2
  • ______g CaCl2
  • 2 plastic weigh boats
  • Electronic Balance
  • 1 graduated cylinder
  • 2 beakers – 250 mL
  • H2O wash bottle (filled with DI water)
  • 1 Stirring rod
  • Ring Stand with ring
  • Funnel
  • Filter paper (1 piece)
  • Goggles

Taken from Grapevine Colleyville ISD, SMG, Experiment 6

Procedure --Day 1

1. Put on and safety goggles, tie hair back. Gather your materials.

2. Using the precise electronic balance from the front of the room, measure our the exact amounts of Na2CO3 and CaCl2 in grams. (You should have the amount in grams from your pre lab. Make sure to zero the balance with the empty weigh boat on it.

Record the exact amount of sodium carbonate and calcium chloride (in grams) in the data section on the next page.

3. Measure out approximately 50 mL of deionized water using your graduated cylinder. Pour about 25 mL into each of the beakers. Add sodium carbonate to one beaker and calcium chloride to the other. Stir until the solids are all dissolved. (Make sure to rinse the stirring rod before switching which solution you stir!)

4. Pour the contents of one of the beakers into the other (combine the liquids), then gently swirl the mixture for 20-30 seconds. Observe the results andrecord these qualitative observations in the data section below. Allow the contents of the beaker to sit undisturbed for 5 min. to see what happens to the suspended solid particles. Meanwhile, proceed to step 5.

5. Obtain a piece of filter paper and put your group’s names on it using a pencil. Weigh and record the mass of the filter paper (make sure to write your names FIRST!), then fold it into quarters. Use the filter paper, ring stand, funnel, and beaker to set up the filtering apparatus shown to the right in figure 6D-1.

6. Use the wash bottle to lightly wet the filter paper in the funnel to keep the filter paper in place. Swirl the flask and its contents to suspend the precipitate in the solution, then pour it carefully and slowly into the filter funnel. It takes time to complete the filtering process so plan to do it in stages. If you pour in too much at once, it will spill over! Use the wash bottle to rinse the remaining precipitate from the flask into the funnel. This process is very slow—give it time! Do not poke at the paper or it may poke a hole, forcing you to start over.

While you are filtering out the product, please work on post-lab question 1-6.

7. Use the wash bottle one last time to rinse the precipitate in the filter paper. This will remove any residual NaCl(aq) that remains with the precipitate.

8. Gently remove the filter paper from the funnel. Unfold it carefully and put it on the back counter to dry. Leave the filter paper until next class.

9. Clean up all your equipment. Rinse all solutions down the sink with copious amounts of water. Thoroughly rinse the beaker, flask, funnel, and graduated cylinder.

10. Wash your hands thoroughly with soap and water before leaving the laboratory.

Day 2

11. Find your filter paper and make sure it is dry by feeling the bottom of the paper. If it is not dry, you may need to leave it for an additional class period.

12. When it is dry, weigh and record the mass of the dry filter paper containing the CaCO3 precipitate.

13. Once you have written down the mass, you may throw away the paper and the product, then wash your hands.

Data

Mass of Na2CO3: ______Mass of filter paper (before): ______

Mass of CaCl2: ______Mass of filter paper with product: ______

Observations from experiment:

Post-Lab Questions and Calculations

Use the data from your data table to calculate the following values and answer the following questions. For the calculations, make sure to show all work and write your answers with units.

Day 1

Na2CO3(aq) + CaCl2(aq)  2 NaCl(aq) + CaCO3(s)

  1. What is the white product that appeared in the solution when the two reactants were mixed?
  1. Where is the NaCl in this reaction? Can it be seen? Why or why not?
  1. Using the exact mass from the data above, calculate the amount of moles of Na2CO3 • H2O used.
  1. Based on your answer to #3, how many grams of CaCO3 can you make?
  1. Using the exact mass from the data above, calculate the amount of moles of CaCl2 used.
  1. Based on your answer to #5, how many grams of CaCO3 can you make?

Day 2

  1. Compare your answers from questions 4 & 5. Which amount of CaCO3 should this reaction produce? Explain why in complete sentences.
  1. How many grams of product did you actually get in the experiment?

(grams of product = mass of filter paper with product—mass of filter paper)

  1. Compare the amount of grams of product you predicted you would get (the amount you calculated above) to the amount you actually got (the amount from your data table). Did you get more, less, or the same amount of product as you predicted? (Write in a complete sentence.)
  1. Scientists often like to calculate the percent yield of a chemical reaction, which is a comparison of the amount of product a reaction actually produced (actual yield) compared the amount of product that was expected (theoretical yield). The formula for percent yield is given below.

Use your numbers from the experiment to calculate the percent yield of your reaction. Show your work.

Actual yield (amount of product you collected, from question 8): ______

Theoretical yield (amount of product you calculated, from question 7): ______

Percent Yield: ______

  1. Chemical reactions never get to 100% yield. What are some of the reasons that we don’t get 100% yield in chemical reactions? Explain in a paragraph.
  1. What are some errors that could have affect your results? Write a short paragraph explaining 2-3 errors and how they affect your experiment. (Note: EVERY experiment has errors! You will receive no credit for saying “our experiment had no errors.” Also, “we messed up the calculations” is NOT an acceptable error!)

Taken from Grapevine Colleyville ISD, SMG, Experiment 6