CHEM 212 Laboratory
Determination of Water of Hydration
Reference: General Chemistry Laboratory Experiments, Suzanne W Slayden, 1999, 3rd edition,
Pages 127-130
Data: After you have noted down all the masses, enter your own data into the appropriate Webbased data entry form, using a computer in the lab. In your measurements and calculations,
remember to pay attention to uncertainties and significant figures.
Results: Outside of class, retrieve your data in spreadsheet form (along with that of the entire
class) from: http://chem.gmu.edu/results/. Then use Excel to calculate the Weight of hydrated
salt, Moles of hydrated salt, Weight of anhydrous salt, Moles of anhydrous salt, Weight of H2O
lost, Moles of H2O lost, Moles of water released per mole anhydrous salt, Theoretical weight
percent of water in hydrated salt, Actual weight percent water in hydrated salt, and % Error.
Your lab report should include the following in addition to the pages from your lab notebook:
 An Excel sheet “Raw Data” showing the raw data for the entire class (as downloaded).
A typical example of the raw data sheet is shown below:
DATA ANALYSIS SUPPLEMENT
RAW DATA
1
2
3
A
g_K3FeOx3_3H2O
12.123
11.867
B
g_K3FeOx3
10.345
9.453
Explanation:
g_K3FeOx3_3H2O = Weight of hydrated salt
g_K3FeOx3= Weight of anhydrous salt

A 2nd Excel worksheet “Results” showing the calculated results for each student in the
class – each in a separate row. Make sure to show an example calculation for each
column. This can be done by copying the equation to a blank cell below the elements in
the table. An apostrophe in front of it makes it text instead of an equation. Each table
should be formatted as in previous classes with lines separating the table headings from
the contents. A line below the contents should also be drawn.
A typical example of the results sheet is shown below:
1
2
3
4
A
Results
B
C
D
E
F
molH2O/
molH2O
molHydratedS molHydrated
massH2O lost mass%H2O lost
alt
Salt
%Error
1.778
14.666
0.099
0.0246
4.024
34.1
2.414
20.342
0.134
0.0241
5.560
85.3
Explanation

Cell
A2
Column Name
massH2Olost
B2
mass%H2O
C2
molH2Olost
D2
molHydratedSalt
E2
molH2O/
molHydrated Salt
F2
%Error
Explanation
mass of H2O lost from the compound after heating. Obtained by
subtracting the mass after heating in the oven from the mass after
heating. E.g. A3 in the results table is calculated by subtracting the
contents of B2 from the contents of A2!
Sample calculation: =RawData!B2-RawData!A2
mass % of water in the hydrated compound.
E.g. =100*A3/RawData!A2
moles of water lost from the hydrated sample
E.g. =A2/18.01
moles of the hydrated salt used
E.g. =RawData!A2/491.25
Mole of water divided by the mole of hydrated compound
E.g. =C3/D3
E.g. = =100*abs(E2-3)/3
An Excel chart showing a histogram of the distribution of Actual weight percent results.
Use equally spaced “bins” chosen to display the “spread” in the class results. Refer to the
histogram tutorial on the website.
Printing Tables:
 Large tables should be printed in the landscape mode and sometimes it might be
necessary to go to “page setup” and select “Fit to 1 page” to make the page fit on one
page.
 Include column and row headings on the printout so that the instructor can more easily
understand equations used. This can be done by going to File → Page Setup → Sheet tab
→ Select “Row and Column Headings”.
Discussion: In your discussion section address the following questions:
o What is a Hydration number?
o How are water molecules bonded to the metal ion or anion? What happens to them on
heating?
o What may happen to the crystal structure and color of a compound when it is dehydrated?
o What are the possible sources of error in this experiment? Refer in your answer to the
class histogram as well as to your own results.
o Discuss your % Error in terms of errors in measurements. What is the major source of
error?
o Using the histogram, discuss how your mole ratio compares with the mole ratio of the
rest of the class.
o Discuss the shape of the histogram. What does it tell you about the nature of the error in
the class’ measurements?