Title: Hydrate Lab
Date: Aug 20, 2024
Experimenters: Shannon Shin, Jason Wang, Yoonseok Choi, Sihyun Kim, Amy Lee
Purpose: The purpose of this lab was to find the proper empirical formula by measuring the mass of
copper that forms.
Safety: We wore safety googles. Copper chloride can irritate that stomach, cause salivation, nausea,
vomiting, stomach pain, and diarrhea.
Materials: Crucible with cover, crucible tongs, spatula, ring stand, ring and clay triangle, lab burner,
50mL beaker, funnel and filter flask, filter paper, watch glass, unknown solid copper chloride hydrate,
aluminum wire, distilled water, wash bottle, balance, glass stirring rod, and heat lamp (oven)
Procedure:
1) Obtain and wear goggles.
2) Measure and record the mass of a clean, preheated crucible and cover. Obtain about 1 g of
the unknown copper chloride hydrate and place it in the crucible. Use a spatula to break up
any large pieces of the substance by pressing the pieces against the wall of the crucible.
Measure and record the exact mass of the crucible with compound and its cover.
3) Set up a ring stand, ring, and clay triangle for heating the sample. Rest the crucible on the clay
triangle with the cover slightly tilted so that vapor may escape. Set up a lab burner and ignite
the burner away from the crucible. Adjust the burner to get a small flame.
4) Hold the burner in your hand and move the flame slowly back and forth underneath the
crucible to gently heat the sample. Do not overheat the compound. (If you overheat the
compound, the copper will burn emitting a green flame.) Note the color change, from blue-
green to brownish, as the water of hydration is driven out of the crystals. When the sample has
turned brown, gently heat the crucible for two more minutes.
5) Remove and turn off the burner. Cover the crucible and allow the sample to cool for about ten
minute
6) Reheat the crucible, crucible lid and sample until constant mass is achieved. Record the final
mass.
7) Once the sample has achieved constant mass, transfer the brown solid to a clean and empty
50 ml beaker.Rinse out the crucible with two 8mL aliquots of distilled water and pour the water
into the 50 mL beaker.Gently swirl the beaker to completely dissolve the solid. Note that the
color of the solution is green as the copper ions are rehydrated.
8) Measure out about 20 cm of aluminum wire, coil the wire, and place the wire in the beaker of
solution so that it is completely immersed in the copper chloride solution. Note that the reaction
produces a gas, elemental copper is forming on the surface of the aluminum wire, and the
color of the solution is fading.The reaction will take about 30 minutes to complete. Go to Step
11 and set up parts a and b while you wait
9) When the reaction is done, the solution will be colorless. Most of the elemental copper will be
on the aluminum wire. Add 5 drops of 6 M HCI solution to dissolve any insoluble aluminum
salts in the mixture, which should make the solution clear. CAUTION: Handle the hydrochloric
acid with care. It can cause painful burns if it comes in contact with the skin.
10)Use a glass stirring rod to scrape off as much copper as possible from the Al wire. Slide the
wire up the wall of the beaker and out of the solution with the glass stirrer and rinse off any
remaining copper with distilled water. If any of the copper refuses to wash off the aluminum
wire, wash it with one or two drops of 6 M HC| solution. Put the Al wire aside leaving the solid
copper in the beaker.
11)Collect and wash the copper produced in the reaction.
a. Set up a funnel for vacuum filtration.
b. Obtain a piece of filter paper. Measure and record its mass, and then place the filter
paper on the funnel. Start the vacuum filtration.
c. Use small amounts of distilled water to wash all of the copper onto the filter paper on
the funnel. Use the glass stirring rod to break up the larger pieces of copper.
d. Wash the copper twice more with small amounts of distilled water.
12) Turn off the suction on the vacuum filtration apparatus, Mass 10mL of 95% ethanol to the
copper on the filter paper and let it sit for about 1 minute. Turn the suction back on and let the
vacuum filtration run for about five minutes. about five minutes.
13)Measure and record the mass of a clean, dry watch glass. Transfer the copper to the watch
glass. Make sure that you have scraped all of the copper onto the watch glass.
14)Dry the watch glass of copper under a heat lamp or in a drying oven for five minutes. Remove
the watch glass and allow it to cool. Measure the mass of the watch glass and copper when
the watch glass is cool enough to touch. Repeat the drying and weighing of the copper until
you achieve a constant mass. Record the final mass.
15)Dispose of the copper, aluminum wire, and filtered liquid as
Pre - Lab Questions:
PRE-LAB QUESTIONS
1. What is the purpose of preheating the crucible and its cover prior to measuring its mass?
- We are trying to evaporate the water molecules to know how much water there is.
2. Washing soda is a hydrated compound whose formula can be written Na_2CO_3 • ZH20, where z is the number of moles of
H20 per mole of Na_2CO_3. When a 2.123 g sample of washing soda was heated at 130°C, all of the water of hydration was
lost, leaving 0.787 g of anhydrous sodium carbonate. Calculate the value of z.
- 1.336g of H_20 - 1 mol of H_20 - 1 mol of Na_2CO_3 - 105.99g of
Na_2Co_3
- - 18.02 g of H_2O - Z mol of H_20 - 1 mol of
Na_2CO_3
= 0.787 g
(1.336*103.99)/(Z*18.02) = 0.787
Z= 9.98 = 10
3. A piece of iron weighing 85.65 g was burned in air. The mass of the iron oxide produced was 118.37 g.
(a) Use the molar mass of iron to convert the mass of iron used to moles.
85.65 g of Fe 1 mol of Fe
55.845g of Fe
=1.543 mol of Fe
1. According to the law of conservation of mass, what is the mass of oxygen that reacted with the iron?
118.37 g – 85.65 g = 32.72g of oxygen
2. Calculate the number of moles of oxygen in the product.
32.72 g of Oxygen 1 mol of Oxygen
16 g of Oxygen
=2.045 mol of Oxygen
3. Use the ratio between the number of moles of iron and number of moles of oxygen to calculate the empirical formula of iron
oxide. Note: Fractions of atoms do not exist in compounds. In the case where the ratio of atoms is a fractional number, such
as ½, the ratio should be simplified by multiplying all the atoms by a constant to give whole number ratios for all the atoms
(e.g., HOx should be H20).
Fe = 1 mol
O = 1.33 mol
Fe= 3 mol
O = 4 mol
Fe_3 O_4
Data Tables:
Qualitative:
Before The Copper Chloride was a blue/teal solid.
During The Dehydrated Copper Chloride turned into brown
chunks of solid/ powder.
After When putting the distilled water on the beaker with
dehydrated Copper Chloride, the color changes
returned back to blue.
Quantitative:
Measurement (w/Units) Value
Mass of Crucible with Cover 21.59g
Mass of Crucible and hydrated sample 22.59 g
Mass of hydrated sample 1.00 g
Mass of crucible and dehydrated sample 22.45 g
Mass of dehydrated sample 0.86 g
Mass of water evolved 0.14 g
Mass of filter paper 1.51 g
Mass of filter paper and copper 1.95 g
Mass of copper 0.44 g
Data Analysis Questions (Calculations):
1. Why must objects be cooled before their mass is determined on a sensitive balance?
Water should be evaporated completely in order to determine the mass.
2. How many moles of water were in your sample of copper chloride hydrate?
0.86g CuCl_2 1 mol CuCl_2
134.45g CuCl_2
= 0.0064 mol CuCl_2
1-0.86=0.14g H_20
0.14g of H_20 1 mol of H_20
18.02 g of H_20
=0.0078 mol of H_20
0.0078/0.0064 = 1.2*5 = 6 mol of H_20
3. How many moles of copper were in your sample of copper chloride?
0.44g of Cu 1 mol of Cu
63.55g of Cu
= 0.0069 mol of Cu
4. How many moles of chlorine were in your sample of copper chloride?
0.0069 mol of Cu 2 mol of Cl
1 mol of Cu
0.0138 mol of Cl
5. Write the proper chemical formula and name for the compound that you tested.
CuCl_2 * 6H_2O
6. Use stoichiometry to calculate the theoretical yield of copper in this experiment based on the
initial mass of your sample.
3CuCl_2 + 2Al -> 2AlCl_3 +3Cu
1 g of CuCl_2 1 mol of CuCl_2 3 mol of Cu 63.55 g of Cu
134.55g of CuCl_2 3 mol of CuCl_2 1 mol of Cu
=0.472 g of Cu
7. Calculate the percent yield of copper actually produced in this experiment.
0.44g / 0.472 g = 0.932 *100 = 93.2%
8. A student fails to place the lid on the crucible during the initial heating of the hydrated sample
and some of the solid spatters out. What effect does this error have on the calculated mass of
the water lost by the hydrate? Justify your answer.
Conclusion:
R We applied the law of definite proportions to determine the empirical formula of
hydrated copper chloride by measuring the mass of the resulting copper.
E We heated Copper Chloride hydrate in a crucible with a Bunsen burner to evaporate
the water molecules. After dehydration, we measured the mass of the Copper
Chloride to determine the amount of water lost. Next, we dissolved the dehydrated
Copper Chloride in water and inserted an aluminum wire, allowing copper to form on
the wire through a reaction. Finally, we collected and measured the mass of the
copper.
R Many types of paint, especially watercolor paint appears to be darker when first
applied but lightens as it dries. Like this experiment, the paint changes color when it is
dehydrated or dried.
U During the lab, some copper was accidentally dropped onto the lab table, but we
managed to recover most of it. Another potential source of error was the possibility
that the analytical balance was not properly calibrated.
N We learned how to use a lab burner for the first time, which will be beneficial in future
experiments. I also discovered that some compounds change color when dehydrated,
which can be a useful indicator in identifying chemical changes involving water
evaporation.
