Introduction
Introduce the background material necessary in order to understand the experiment. State the purpose of the
investigation in the form of a sentence – do not phrase it as a question.
When crystallization occurs due to evaporation of the water from an aqueous salt solution, water
molecules may become incorporated into the structure of the crystal. When this occurs, the resulting
salt is known as a hydrate. A hydrate may have any number of water molecules incorporated into its
structure, but the ratio of water molecules to salt units will always occur in simple whole number ratios.
By heating the hydrated salt, the water molecules can be driven off by evaporation, producing the
anhydrous form of the salt. The purpose of this investigation is to dehydrate a hydrated salt of copper
(II) sulphate, CuSO4·x H2O, in order to determine its chemical formula.
Apparatus and Materials
Apparatus refers to the equipment used, where materials refers to the chemicals/substances.
Only list items that you used in the experiment, as you may have been asked to deviate from the items listed in your
lab sheet.
Apparatus
apron
eye protection
crucicle and lid
crucible tongs
iron ring
ring stand
bunsen burner
wire gauze x 2
centigram balance
Materials
4 grams of CuSO4·x H2O
Procedure
List and enumerate the steps you performed. Again make sure you do not include steps that you did not actually
do.
Use the past passive tense. “Past” obviously refers to the fact it was performed in the past, “passive” refers to the
fact that you never say who was doing the action. In other words, if you are thinking in terms of regular passive
tense, use the object as the subject.
1. A clean, dry crucible and lid were placed on wire gauze in a ring stand, with the lid slightly ajar.
2. Using the Bunsen burner, the crucible and lid were heated strongly for three minutes.
3. The crucible and lid were removed from heat using the tongs, and placed on another piece of
wire gauze to cool.
4. The hydrate was placed in the crucible, and massed.
5. With the lid slightly ajar, the crucible and its contents were heated gently for approximately 15
minutes.
6. The crucible and contents were removed from heat and allowed to cool on wire gauze.
7. The mass of the crucible, lid and contents were recorded.
8. The procedure above was repeated once more.
9. The copper (II) sulphate was disposed of, and lab stations were cleaned.
Observations
Unless you are instructed to do otherwise, do not include indirect observations in your observation section. This
means calculations derived from your raw data. Only include the observations (qualitative and quantitative) that
you observed during the lab itself.
Trying to incorporate both qualitative and quantitative observations into one table may be cumbersome. If this is
the case, the qualitative observations need not be in a tabular form – point form either before or after the
quantitative observations is fine.
Object
crucible + lid (empty)
crucible, lid + hydrated salt
crucible, lid + anhydrous salt
Mass (g)
25.77
29.80
28.35 g (Trial 1)
28.35 g (Trial 2)
Qualitative observations
Salt is a dry, blue crystal
Salt is a dry, whitish-gray powder
Analysis
You must show all work (formulas used, subbing in), and clearly separate your steps so that it is easy to interpret. If
you are doing multiple similar calculations (e.g., finding number of moles from molar mass), you only need to show
one full calculation with the formula.
Mass of hydrated salt = (crucible, lid + hydrated salt) – (crucible + lid)
= 29.80 g – 25.77 g
= 4.03 g
Mass of water lost = (crucible, lid + hydrated salt) – (crucible, lid + anhydrous salt)
= 29.80 – 28.35 g
= 1.34 g
*note, the mass of the crucible and contents after heating that was used in the calculation is the
arithmetic mean of the two trials.
Mass of anhydrous salt = (mass of hydrated salt) – (mass of water lost)
= 4.03 g – 1.34 g
= 2.69 g
CuSO4
M = 159.61 g/mol
m = 2.69 g
H2O
M = 18.02 g/mol
m = 1.45 g
n = m/M
= 2.69 g/(18.02 g/mol)
= 0.0162 mol
n = 0.0162 mol
CuSO4 : H2O
0.0162 mol: 0.085 mol
0.0162 mol 0.0805 mol
:
0.0162mol 0.0162mol
1 : 4.97
The chemical formula of the hydrated salt is therefore CuSO4·5 H2O.
Discussion
Discuss how you analyzed your data, and the results of your analysis. Do not be overly verbose; the point is to
provide a concise overview of your analysis so it is not necessary to include a description of every single step. The
steps you undertook should be apparent in your analysis section.
Identify any possible sources of error. You may also want to suggest improvements to the lab procedure that would
help minimize error. Again, use past passive tense – never speak in the first person. When in doubt, state
everything as a fact (never use “I think...”).
After two trials of dehydrating the CuSO4·x H2O, the mass was found to be constant and so no more
trials were performed. The arithmetic mean of the two trials was used as the experimental value when
analyzing the data. The mole ratio of anhydrous CuSO4 to H2O was determined to be approximately 1:5,
allowing identification of the hydrated salt as CuSO4·5 H2O. The actual mole ratio of CuSO4 : H2O was 1 :
4.97. Possible sources of error include human error during the process of transferring and measuring
the salt. The mole ratio, however, was sufficiently close enough to simple whole numbers such that the
chemical formula derived from the dehydration analysis can be deemed accurate.
Conclusion
Simply restate the purpose of the lab, provide a concise summary of the lab procedure, and restate the conclusion
of your analysis. Never introduce any new information in the conclusion; this should all have been established in
your introduction or discussion, if necessary. There is no need to restate all the background information from your
introduction; avoid redundancy. If anything went horribly wrong to the point where no valid conclusion can be
reached from your data, you should mention it here as well as in your discussion.
The purpose of this lab was to determine the number of water molecules incorporated into the
structure of CuSO4. Through dehydration analysis, the chemical formula of the hydrated salt was
determined to be CuSO4·5 H2O.
Final points on organization:
 Put all sections in the correct order
 Use proper grammar and spelling
 Subscripts
 Data tables that are redundant or difficult to interpret will cost you marks
 Never split up data tables/steps of analysis on separate pages. Use a page break if you have to – a little
blank space is better than splitting elements up.
 Do not use the word “reveal/revealed”. Try “identify” or “determine”.
 Notice the word “concise” was used several times. BE CONCISE!!!!