Exp. 4:
Hydrates
Required Locker Materials:
-
Crucible
Crucible tongs
Clay triangle
Safety:
-
Eyewear MUST be worn at all times
Waste:
-
All solid waste needs to be disposed
into waste containers
Experimental Objective:
The objective of the lab is to determine the mol ratio between the anhydrous salt and the
amount of water in the crystal structure of the hydrate. The Lab is structured into two
parts: In the first part students learn the technique how to determine the formula of copper
sulfate hydrate. This will also expose the students to mol calculations. In the second part
students are given an unknown hydrate, in which the unknown mol ratio between
anhydrous salt and water must be determined.
Procedure
(Part 1) Determine the formula of copper sulfate hydrate
For this experiment record all observations and measurements in your notebook:
1. Set up a bunsen burner and crucible on a clay triangle. Make sure that the Bunsen
burner is located toward the middle of the bench.
2. Vigorously heat the crucible for about three to five minutes in order to burn of any
impurities and water.
3. Remove the burner. Let the crucible cool to skin temperature, at least. Do not handle it
directly with fingers anymore because the skin may transfer minute unwanted, oil
particles. Carry the dish with either Kimwipes or crucible tongs.
4. When the crucible is cool enough weigh the mass of the empty crucible.
5. In a small beaker weigh out approximately 0.5 to 1.0 g of hydrated CuSO4 (you do not
need to write down this mass). Go to your Lab place and put the CuSO4 into your
crucible. Go back to the balance and weigh now the mass of the crucible and salt.
6. Return the dish and salt to the triangle, and gently heat for 15 minutes or so with a low
blue flame. Check the color of the crystals now and then. Do not over heat them,
because CuS04 can decompose to black CuO if the temperature gets extremely hot.
7. Near the end of the heating, move the flame around the sides and top to make certain
all of the water has been removed. Mash up the powder with a dry spatula.
8. Let the contents cool to room temperature, and then weigh the mass of the crucible with
the anhydrous salt.
9. Repeat heating, but heat for only 5 minutes. If the weight does not differ by more than
5 mg, then you can assume the dehydration is complete. If the difference is larger than
5 mg you need to repeat this step until the mass difference between two heatings is less
than 5 mg. Make sure you write down the mass after each heating!
10. Rinse out the dish with a little water and write down your observation.
11. Dispose the solid waste in the container and clean your crucible with water.
12. Repeat this procedure at least one more time in order to have two “good” trials.
(Part 2) Determine the mole ratio of an unknown hydrate
It is recommended that students start a new table for the measured data in part 2.
13. Receive an unknown hydrate from the instructor and write down the sample number.
Exp. 4
Page 1 of 2
Leo Truttmann – Fall 13
14. Repeat steps 2 to 11 with the unknown hydrate at least one more time until you
obtained two “good” trials.
Template for Measurements
Part__: Measurements
Trial 1
mass(dish)
[g]
mass(dish + hydrate)
[g]
mass(dish + anhydrous) / 1st heating
[g]
mass(dish + anhydrous) / 2nd heating
[g]
mass(dish + anhydrous) / 3rd heating (if necessary)
[g]
Trial 2
Trial 3
Calculations
For the calculation start a new section in your notebook. Remember you need to show
every calculation you do by writing down the equation and an example calculation. The
example calculation only needs to be done for one trial. The results of the remaining trials
can be written down in a table in your notebook.
(Part 1) ) Determine the formula of copper sulfate hydrate
Mass of hydrate
To find the mass of the hydrate in your crucible you have to take the difference between the
mass of the crucible plus hydrate minus the mass of the crucible.
Mass of anhydrous salt
Same as above except this time you need to use the mass of the crucible with the
anhydrous salt.
Mass of water lost
Obviously this is the difference between hydrate and anhydrous salt.
Moles of water and anhydrous salt
Using the molar masses of each the number of moles for water and anhydrous salt can be
calculated.
Mole ratio
The mole ratio is the ratio between moles of water and moles of anhydrous salt.
Average mole ratio and Average Deviation of mole ratios
Calculate the Average and Average Deviation of your best two trials.
Formula of copper sulfate hydrate
Write down the correct formula for the copper sulfate hydrate.
(Part 2) Determination of the density of the unknown element
The calculations for part 2 are almost identical to the calculations in part 1. The difference
is that you have to use the given formula mass for the unknown anhydrous salt in order to
calculate the moles of anhydrous salt.
Exp. 4
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Leo Truttmann – Fall 13