EXPERIMENT 23 – THE FORMULA OF A HYDRATE
Name________________ Per _____
OBJECTIVE: To find the formula of a hydrate and review mass relationships in chemical reactions.
MATERIALS:
ring stand
crucible and cover
tongs
hydrate, MgSO4•_____H2O
balance Bunsen burner
clay triangle
spatula
PROCEDURE:
1. Obtain a clean crucible and cover.
2. Weigh the crucible and cover on a balance. Record
this and all successive weighings to 0.01 g.
3. Put about 3 g of the hydrate sample in the crucible,
replace the cover and weigh.
4. Place the crucible on the clay triangle on a ring stand.
With the cover on the crucible slightly ajar as in Fig.
1, heat the crucible and its contents, strongly, for
approximately 8-10 minutes.
5. Slide the lid to completely cover the crucible and
allow it to cool. When they are at approximately
room temperature, weigh the crucible, cover, and
contents and record the mass.
DATA:
Anhydrous salt formula
MgSO4
Mass of empty, dry crucible and cover
__________ g
Mass of crucible, cover and hydrate sample
__________ g
Mass of crucible, cover and anhydrate salt
__________ g
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EXPERIMENT 23 – THE FORMULA OF A HYDRATE
CALCULATIONS AND QUESTIONS:
1. Calculate the (show work):
Mass of water lost
Moles of water lost
Mass of anhydrous salt
Moles of anhydrous salt
2.
Find the following ratio and then express as a simple whole number ratio.
a. Using the answers above, obtain the ratio:
moles of water lost
moles of anhydrous salt
=
__________
=
_______ : _______
b. Write the formula for the original hydrate by rounding off the above ratio to the nearest whole number.
MgSO4 · _____ H2O
3.
Consider what effect the following errors would have on the coefficient for the moles of water in the above
formula if (Circle the correct change below).
a. the student did not drive off all of the water from the hydrate.
increase, decrease or remain the same
b. the student used a damp crucible and did not dry it before adding the hydrate.
increase, decrease or remain the same
c. after the last heating the student allowed the crucible and contents to cool overnight in the damp air
before weighing.
increase, decrease or remain the same
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EXPERIMENT 23 – THE FORMULA OF A HYDRATE
EXTENSION-SOAPY WATER
Materials: cap, towel, penny, pipette, water container, soapy water container
1. Set a dry penny on top of a dry cap.
2. Dispense enough drops of water on top of the penny to nearly overfill it (20-30 drops).
Describe the appearance of the water on the cap. (Hint: Look across at eye level)
__________________________________________________________________________
3. Poke the water surface with the pipette tip. What happens?___________________________
Immerse the pipette in soapy water. Then poke the surface with the soapy water.
What happens?________________________________________________________________
(If you chose to repeat steps 1 -3, use a NEW pipette.)
4. What property of water caused the bead of water to form on the penny? ______________________
5. Define that property. _______________________________________________________________
________________________________________________________________________________
6. What visible affect did the soap have?__________________________________________________
7. On a molecular level, what affect did the soap have?_______________________________________
_________________________________________________________________________________
8. In this demonstration soap acted as a ________________.
RETURN ALL MATERIALS (INCLUDING RUBBER BULB), AFTER DISCARDING
THE USED PIPETTE(S).
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EXPERIMENT 23 – THE FORMULA OF A HYDRATE
EXTENSION: PAPER CHROMATOGRAPHY
Purpose: To learn chromatography, characteristics of dyes, pigments, solvents and paper interactions.
Materials:
coffee filter
tap water
25mL graduate
dry 400mL beaker
towel
black Sharpie marker
fine tipped water-soluble markers
Black Sharpie
Procedure:
1.
Using a black Sharpie and five (include black) different
water-soluble markers, place a single dot at the ‘bend’
of the coffee filter. Note the placement of
brands/colors on the diagram.
2.
Carefully add 25mL of water to the DRY 400mL beaker. Do not splash or wet the walls of the beaker.
3.
Carefully bend the filter into a ‘V’ (cone shaped). Insert the filter into the beaker so the point of the
cone is in the water. The water will get pulled through the tiny tubes in the paper, dissolve the ink and
separate it into different pigmented molecules. Leave the filter in the water undisturbed until the
solvent reaches the top edge of the paper (about 20 min.).
4.
Remove the filter to end the run and place it on a dry towel. Discard when finished.
Analysis:
1.
Dyes that are most attracted (most similar) to water are carried with the water, and dyes that are least
attracted will ‘stick’ closer to the point of application. The dyes most attracted to water are small/large
(circle one) molecules and polar/nonpolar (circle one) in nature.
2.
Which color dye is most attracted to water? _______________ Least? ___________________
3.
What color dyes are present in black ink? __________________________________________
4.
The Sharpie ink did not flow but stuck to the point of application. Why? _________________
______________________________________________________________________________
5.
What might experimentally be altered so that the Sharpie’s flow would be similar to that of the other
black marker? ______________________________________________________________
Explain. _______________________________________________________________________
______________________________________________________________________________
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