Name: ______Date: ______Pd. ______
Determining the Empirical Formula of a Compound Containing Copper and Chlorine
Purpose of the Experiment:
Determine the empirical formula of a compound containing copper and chlorine. You will determine the empirical formula of copper chloride, by reacting a measured volume of aqueous copper chloride solution with Zinc, then massing the solid elemental Cu produced.
Background information:
A compound is a substance of two or more elements. The empirical formula of a compound is an expression of the simplest whole-number molar ratio of the elements making up the compound.
According to the law of constant composition, the molar ratio of elements in a specific compound is constant, regardless of the compound’s source or method of preparation. Once we determine the individual masses of each element composing a specific compound, we can determine the empirical formula of that compound.
Procedure:
Notes:
· Record all masses to either the nearest milligram (0.001g) or nearest centigram (0.01g) depending on the scale used.
· Record all data on your Data and Observations sheet
· Dispose of all solids and solutions as indicated by your teacher
1. Obtain 25.0mL of the copper chloride solution.
2. Obtain the mass of a clean 50mL beaker.
3. Transfer the Copper Chloride solution into the clean 50mL beaker.
4. Obtain a 2-3 g piece of Zinc. Record the exact mass of the Zinc.
5. Tilt the 50mL beaker slightly. Using forceps, transfer the weighed Zn into the copper chloride solution. Allow the Zn to gently slide down the inner beaker wall, in order to avoid any solution loss due to splashing.
6. Stir the reacting mixture with a clean, glass stirring rod, so that the solid Cu product will not adhere to the Zn. Continue stirring until the blue color has disappeared. This may take a few minutes.
7. Ask the teacher, to add 5-10 drops of 0.10 M HCl to the solution. Thoroughly stir.
8. Using the forceps, remove all unreacted Zn from the solution. Wash any Cu adhering to the Zn back into the beaker, using the wash bottle. Dry the Zn with paper towels. Determine and record the mass of the dried Zn. Discard the Zn in the beaker provided.
9. Carefully decant (pour off) the colorless solution from the 50mL beaker into a second beaker. Discard the solution in the waste beaker provided.
10. Rinse the solid Cu as follows, in order to remove and zinc chloride adhering to it. Pour 10mL of distilled water into the 50mL beaker containing the Cu. Stir the mixture thoroughly with a stirring rod. Allow the Cu to settle and decant the liquid into an empty beaker.
11. Place the 50mL beaker containing the Cu on the hotplate. Under medium heat, heat the beaker until the Cu has dried. When the Cu has dried, turn off the hot plate and allow the beaker to completely cool.
Pay attention to your beaker during this process. Due not over heat the beaker.
12. When cooled, mass the beaker containing the Cu. Discard the Cu into the waste beaker provided.
13. Using dish soap clean all glass ware and put all materials away.
Date Table
Mass (g)Mass of 50mL beaker (2)
Mass of Copper Chloride in solution
Mass of Zn (4)
Mass of Zn after drying (8)
Mass of Cu and beaker (12)
Calculations:
1. Mass of copper chloride in the solution.
2. Calculate the mass of Cu produced.
3. Calculate the mass of Cl in the original CuxCly sample.
4. You now have the mass of Cu and mass of Cl from your original CuxCly sample. Using your notes on how to calculate empirical formulas, calculate the empirical formula for the compound containing Cu and Cl.
You now have the mass data that is usually given to you in word problems. Follow the same steps as you have used to calculate the formulas from the practice ws.
5. Calculate the mass of Zinc used up in the reaction. (Hint: Not all the zinc was used in the reaction)
6. Calculate the number of moles of Zinc used in the reaction with the copper and chlorine solution.
Conclusion (review) Questions:
1. Write the complete chemical equation for the reaction produced in this experiment.
1a. What type of reaction is this? ______
2. Ethylene glycol (C2H6O2) is commonly used as antifreeze in automobile radiators. What is the empirical formula of ethylene glycol?
3. What is the difference between Empirical and Molecular formulas?
4. In this lab we dealt with the compound CuCl2. What is the percent composition of Cu and Cl in the compound?