Name: Zachary Mattson Score___________/50
Lab Day: Monday TA: Tim Lamb
Introduction
The reason for this experiment was to determine what the degree of hydration was for several
different hydrates. A hydrate is a salt that can incorporate water molecules into their crystal
structures. Whereas anhydrous is a salt without water in their crystal structure. The goals of the
experiment could be met by taking a known amount of a hydrate, applying heat to it, then
remeasuring the mass of the now anhydrous compound. By taking a post heat mass we can
determine how much was H2O and how much was the salt compound. After finding how many
grams of each substance we had we can determine how many moles of each were contained
within the hydrate. Then by division we can determine the degree of hydration for that
particular hydrate. For example CaSO4 •5.3H2O(s) + ∆ → CaSO4 (s) + 5.3H2O(g)
Materials and Methods (A.K.A. Experimental)
For the lab first I took out four separate crucibles and their lids and I marked them
individually to be able to keep track of which one was which (for accuracy purposes as well).
Next I prepped the Bunsen burner, and placed the mesh wire above it to hold the crucibles.
After that I took my four marked crucibles and weighed them individually. After acquiring their
weights I put approximately 1 gram of the 4 different Hydrates (making sure to note the actual
amount). Then I took my four crucibles back to my station and set them all on a source of heat
(one on the burner and three on the hot plate). After several minutes I took all of them off and
put them on another wire mesh to cool down. Once they were cool I took them to the balance
and acquired their first post heat mass and repeated the heating and cooling process. After
acquiring a second post heat mass for each I determined which compounds were not
completely anhydrous and I repeated the heating and cooling processes for those. After
acquiring all of the anhydrous masses I was able to determine how many grams of H2O were in
each compound and then what the degree of hydration was for each compound.
Post-lab: Determining the Degree of Hydration
for Some Metal Salts
***Replace the red text above with your own words. These
sections must be typed**
**For the data table and calculations sections, you may print out this page and show data and
calculation setups by hand, or type the calculations using the equation editor in Microsoft Word
(click insert→equation**
Data
Fill in your raw data for one of the metal salts. Remember to record the full precision of the
balance and include units with your measurements!
Metal salt used: MgSO4
Mass of empty crucible
46.271
Mass of crucible + hydrate
47.311
Mass of crucible with anhydrous salt:
after 1st heating
46.785
after 2nd heating
46.783
Calculations
Show calculation steps for each of the values indicated below. Include units throughout all
calculations and answers and round your answers to the correct number of significant figures.
Mass of hydrated salt
Mass of Crucible with hydrated salt minus mass of crucible without
47.311-46.271=
1.04
Mass of anhydrous salt
Mass of crucible with solid before heating minus mass after heating
47.311-46.783=
.528
Moles of anhydrous salt
Grams of anhydrous salt divided by molarity
.528g(1mol/120.366g)=
.004387
Mass of water
Mass of hydrated salt minus mass of anhydrous salt
1.04-.528=
.512
Moles of water
Grams of water divided by molarity
.512g(1mol/18.02g)=
.02841
Mass % of water
Mass of water divided by mass of hydrated salt
.512/1.04
49.23%
Degree of hydration
Moles of water divided by moles of anhydrous salt
.02841/.004387
6.47
Formula of this hydrate:
MgSO4 •7H2O(s) + ∆ → MgSO4 (s) + 7H2O(g)
Formulas of other hydrates
CuSO4 •5H2O(s) + ∆ → CuSO4 (s) + 5H2O(g)
MgSO4 •7H2O(s) + ∆ → MgSO4 (s) + 7H2O(g)
Fe2(SO4)3•9H2O(s) + ∆ → FeSO4 (s) + 9H2O(g)
CaSO4 •2H2O(s) + ∆ → CaSO4 (s) + 2H2O(g)
Questions
1. Were the formulas you determined exactly correct (no rounding)? If not, suggest 2-3
reasons for any discrepancies and explain how these errors might be mitigated. Simply
saying “human error” or answering “yes” to the question above will get you no credit!!
They were not all exactly correct. Some reasons for discrepancies could be using a different
balance while massing the same compound, not using gloves while transporting the crucible,
and not heating the hydrate for long enough. All of these can yield skewed results. Using a
different balance could yield inaccurate data if the balances are not completely accurate then
using two inaccurate balances could result in incorrect data. Not using gloves could also hinder
the results since fingerprints add mass to the crucible. Finally not heating the hydrate for long
enough would give us inaccurate data since we would be using the acquired mass of a salt that
is not completely anhydrous.
2. Suppose a student, eager to get out of such a fun experiment early, did not allow their
sample to completely dehydrate. In what way (too high or low) would this affect their
experimentally determined degree of hydration? Explain your answer for full credit.
If they did not allow their sample to completely dehydrate then their degree of hydration would
be lower than it actually is. This would be so because some of the mass that they thought was
the anhydrous compound would actually be H2O. Therefore while finding the molar mass of the
water and the anhydrous compound they would be getting incorrect data that would lead to a
smaller degree of hydration.
3. A 2.352 g sample of iron (III) nitrate hydrate was heated to drive off the water in the
sample. If 1.425 g of anhydrous iron (III) nitrate were recovered, what is the degree of
hydration for this compound? Show the complete calculation below.
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