Lab 5 Worksheet

Download the .pdf file of the lab handout here.

Experimental Procedure and Data

1. Label a 250 mL beaker as “A.” Weigh beaker and record your measurement in the data section.

2. Using an analytical balance and disposable weigh boats, weigh approximately 0.50 g CuCl2 • 2 H2and 0.25 g Aluminum foil. Record the exact weight in the table below.

3. Place the Al and CuCl2 • 2 H20 into beaker “A”. Make sure that the aluminum foil is unfolded so that it will completely react.

4. Label a second 250 mL beaker “B”. Weigh and record.

5. Using a balance and a new disposable weigh boat, weigh out 0.70 g of CuCl2 •22 H20 and 0.05 g of aluminum.

6. Place the Al and CuCl2 • 2 H20 into beaker “B”. Again, make sure that the aluminum foil is unfolded so that it will completely react.

7. Look at the contents of each beaker. Record the color of substances and any other observations (odor (waft), bubbling, heat formation, etc.) that are visible at the beginning of the reaction in the data table.

Which reactant do you THINK is in excess in each beaker? WHY???? Record this in your data section.

8. Using a graduated cylinder, measure 50.0 ml of distilled water and add to each beaker. When water is added to the beakers, the CuCl2 •2 H2O will dissolve and the reaction will proceed.

9. Stir the substances in the beakers occasionally with the stirring rod. The reaction should take about 30 minutes to complete.

10. Record any color changes or any other observations as the reaction proceeds in the data table.

11. As the reaction proceeds, record your observations (color changes, bubbling, etc) in the data table.

When the reaction has finished, evaluate the beaker: which reactant do you THINK (based on your observations) is in excess in each beaker? WHY???

12. When the reaction is complete and you no longer notice bubbles forming, if there is excess aluminum foil still observed in the beakers, add 6 M HCl in 1 mL portions under the hood until the foil is completely reacted and no longer visible (but do not add more than 5 mL). Stir to dissolve.

13. Allow the solid Cu to settle in both beakers. Decant (pour off the liquid) the solution from the beakers into a waste container. Be careful not to lose any of the copper.

14. Wash the copper solid with 15 mL of deionized water. Let solid settle. Decant (be careful to pour as much water off as possible without losing any of the copper solid). Repeat once more.

15. Wash the copper solid with 10 mL of methanol. Let solid settle. Decant.

16. Under the hood, heat the beakers on a hot plate at a low setting until dry. Avoid heating at high temperatures for longer periods of time which may cause the unwanted oxidation of the copper product.

17. When the product appears dry, carefully place the beaker on wire gauze or paper towels (do NOT place directly on the counter as the glassware could shatter).

18. After cooling, weigh the beaker and its contents. Record this in your data section.

Pre-Lab Assignment Questions

1. Given the unbalanced equation __ Na + __Cl2→ __ NaCl

If 10.0 g of Na and 14.0 g of Cl2 are reacted together in a lab experiment.

a) Balance the equation.

b) What is the limiting reagent? Show your calculations for each reactant.

c) What is the maximum number of moles of NaCl that can be formed?

d) What is the maximum number of grams of NaCl that can be formed?

e) Calculate the number of moles of each reactant used.

f) How many moles of the excess reactant will be remaining?

2. What would be the benefit of having a limiting reagent when performing a lab experiment? Why not simply make both reactants go to completion?

3. Can we tell from just the masses which of the two reactants will potentially be the limiting reagent? Explain why or why not? Keep in mind what is happening at the molecular level in a chemical reaction.

Experimental Data and Results

  Beaker #A Beaker #B
Mass of Empty Beaker    
Grams CuCl2 • 2 H20  
MM CuCl2 • 2 H20    
Mol CuCl2 • 2 H20    
Theoretical Yield of Cu (if CuCl2 • 2 H20 is limiting)    
Grams of Al    
Moles of Al    
Theoretical Yield of Cu (if Al is limiting)    
Observations Before the Reaction Begins    
Observations After Reaction is Complete    
Mass of Beaker and Solid Cu    
Mass of solid Cu formed during reaction    
Moles of solid Cu formed during reaction    

*Calculations: For full credit, clearly show all calculations with all units labeled.*Show an example calculation for every box for Beaker A for full credit.

Beaker A Beaker B
Theoretical mass of Cu produced if CuCl2 • 2 H20 was the limiting reagent
Theoretical mass of Cu produced if Al was the limiting reagent
What is the Theoretical Yield?
What was the limiting reactant?
What was the % yield of the reaction?

Results, Discussions and Post-lab Questions

1. In these experiments, when and why did the reaction stop? Explain your answer at the particle level in regards to reactants available.

2. If we began the experiment with 0.70 g of CuCl2 • 2 H20, according to the stoichiometry of the reaction, how much Al should be used to complete the reaction without either reactant being in excess? Show your calculations.

3. Give two errors that could have occurred in your experiment. How would each have affected your percent yield?