Stoichiometry Lab:
Determining the Empirical Formula of a Compound
Materials:
•
Sample of unknown copper chloride
•
250 mL beaker/cup
•
Electronic balance
•
Aluminum coil
•
DisClled water
•
Funnel
•
Ring stand with ring
•
Filter paper
•
Pencil (a pen is NOT OK!)
•
Hot plate
•
SCrrer
Safety:
•
Copper chloride is toxic by ingesCon and inhalaCon. It may also cause skin burns and should be handled with cauCon. •
Exercise cauCon while using the hot plates – you will have these on low heat se1ngs so we do not burn the filter paper
Procedure:
1. Find and record the mass of the empty beaker/cup
2. Add approximately 1 gram of the copper chloride to the beaker/cup and record the exact mass
3. Add approximately 40-­‐50 mL of disClled water to the copper chloride and swirl to completely dissolve
4. Be sure all of the copper chloride has dissolved before moving on! (soluCon should be blue)
5. Drop an aluminum coil into the soluCon. The reacCon will take 30-­‐60 minutes to complete (You might want to check it every 10 minutes or so and shake off the layer of copper that forms around the aluminum coil, it will look like rust)
6. Once the soluCon has lost all of its blue color, remove the aluminum from the soluCon. Make sure to knock off as much of the copper precipitate as you can.
7. Using a PENCIL, write your name on the filter paper and the record the mass of the dry filter paper as well
8. Set up a filtering apparatus using a ring, ring stand, funnel, your filter paper, and an empty beaker
9. Filter the copper from the soluCon. You may use a wash boble with disClled water to rinse out all of the precipitate
10. When finished filtering remove the filter paper, open up the filter paper and take care that you do not lose any of the copper
11. Place the filter paper on a hot plate with the heat on low. Allow the paper to dry for 10-­‐15 minutes and record the mass. Keep repeaCng this unCl the copper is dry.
Mass of Empty cup
Mass of cup and chloride sample
Mass of dry filter paper
Data Table:
CalculaCons:
Post lab Analysis:
1.Use the data gathered to determine the empirical formula of the copper chloride (show calculaCons in box above)
Mass of filter paper + copper (1st drying)
Mass of filter paper + copper (2nd drying)
Mass of filter paper + copper (3rd drying)
2.If some copper remained on the aluminum coil instead of being filtered, what effect would this have on the calculaCon of the empirical formula?
Total Mass copper/
chlorine sample
Total mass of copper precipitate
3. If the filter paper is not dried to a constant mass, what effect would this have on the empirical formula?
Pre-­‐lab quesAons to check for understanding:
1. In this experiment, the copper that is dissolved in soluCon originally (blue in color) will precipitate out and form a solid product that looks similar to rust (even though it is pure copper!). Since the copper precipitate is what we are interested in, please explain how we will recover the copper from the soluCon.
2. Why is it important to know the mass of the dry filter paper before we start the filtraCon?
3. How will we know when our recovered copper sample is dry?
Below you will find some sample data collected from CalculaCons:
a similar experiment. In this experiment a copper strip is placed in a gold chloride soluCon and the pure gold precipitates out of soluCon. We would like to know the empirical formula of the gold/chloride compound. On a side note, I am really interested in this because I need to know if the amount of gold in my sample is enough to jusCfy buying the copper I need to perform the reacCons. To recover the gold we filtered the gold precipitate and then dried the gold sample. Use the data in the table below to calculate the empirical formula of the gold compound. Mass of Empty cup
5.6 g
Mass of cup and gold/
chlorine sample
21.15 g
Mass of dry filter paper
0.47 g
Mass of filter paper + gold (1st drying)
14.3 g
Mass of filter paper + gold (2nd drying)
10.67 g
Mass of filter paper + gold (3rd drying)
10.67 g
Total Mass gold/chlorine sample
15.55 g
Total mass of gold precipitate
10.2 g