Empirical molar mass of each hydrate. Note the

Empirical Formula of a Hydrate LAB



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The aim of this experiment is to discuss the empirical
formula for and unknown hydrate and understand what and the empirical formal
represents and the relationship between and the use of hydrate and anhydrous



1.     Find the mass of a clean, dry

2.     Your teacher will provide you
with your hydrated copper sulfate.

3.     Find the mass of the unknown
and crucible together.

4.     Heat crucible with hydrate
until all color has left the hydrate.

5.     Calculate the molar mass of
each hydrate.   Note the amount of water being evaporated from the
compound as it is being heated. Which of the above hydrates do you think is
closest to the hydrate in your crucible?

6.     Once heated sufficiently to
lose the color, remove the crucible to the tabletop and allow to cool until
comfortable to the touch.

7.     Remass and record the mass.

8.     Reheat for a shorter period
of time. Cool.  Remass.  The mass values should not exceed ±0.010 g
of each other.  If they do, repeat the process until you are within

9.     Finally, add some water to the anhydrate to hydrate the
compound again. Record your observations


(Procedure from the
document of instruction from Ms.Riffle)

Data collection

1.     Qualitative Data


For the experiment done, the trial have the reaction
of the copper sulfate to heat.

It can be seem that the copper sulfate form
a color of a bright blue crystal, which is the natural form before the salt, is
exposure toward the heat.

However, after the first heating, it is
obviously seen that the heated copper sulfate transformed color into
whitish-gray form.


2.     Quantitative Data



Table 1

Effect of Heat on Copper Sulfate


Mass of Crucible (g)

Mass of Crucible with Hydrate (g)

Before Heating

Before Heating

After 1st Heating

After 2nd Heating







Data Table 2


Before heating


After heating

Steadily becomes lighter and eventually
changes to white


Processed Data


Table 3

Mass of Evaporated water (H2O) from Hydrate
– Systematic


Mass of crucible with hydrate (g)

Mass of Evaporated water (H2O) (g)

Absolute Uncertainty of Evaporated
water (H2O) (g)

Percent Uncertainty of Evaporated water
(H2O) (%)


Before Heating





Mass of evaporated water is calculated

Mass of Crucible with Hydrate (before heating) –
Mass of Crucible and Hydrate (after heating)

Absolute uncertainty

It has the same unit of the value of the mass of
the crucible

Percentage Uncertainty

(Absolute Uncertainty  Mass of Evaporated water)

Calculating the mole of water (H2O)

Mole of water
= Mass of Evaporated H2O molar mass of H2O

= 0.7 g (25.18)

= 0.0389 (25.18)
mole of H2O


Data Table 4

Mass of Anhydrous
Copper Sulfate (CuSO4)


Mass of the
crucible with hydrate after heating

Mass of the

Mass of Anhydrous
Copper Sulfate (CuSO4)

Absolute Uncertainty
of Anhydrous Copper Sulfate (CuSO4)(g)

Percentage Uncertainty
of the mass of Anhydrous Cooper Sulfate (CuSO4)







Mass of Anhydrous Copper Sulfate (CuSO4) is calculated

Mass of Anhydrous Copper Sulfate = Mass of
crucible with hydrate after heating –
Mass of crucible

Calculating the mole of Anhydrous Copper Sulfate

Mole of CuSO4 = mass of anhydrous CuSO4  molar mass of CuSO4

 = 2.00 g (10.00)

 = 0.01253 (10.00)
mole of anhydrous CuSO4

Data Table 5

Ratio of Anhydrous Copper Sulfate (CuSO4)
with Water (H2O)

Amount of Anhydrous
Copper Sulfate  (10.00

Amount of Water (H2O) (25.18

Mole Ratio





Calculating the Mole Ratio of Anhydrous Copper
Sulfate (CuSO4) and Evaporated Water  (H2O)

= 0.0389 (25.18)
mole of H2O  0.01253 (10.00)
mole of CuSO4

= 3.104 (35.15)

Accordingly, it means that there is 1 mole of
Copper Sulfate (CuSO4) for every 3 mole of
Water (H2O)


Therefore, the
chemical formula of this unknown hydrate is
CuSO4 5H2O, and the name of the hydrate is called Copper Sulfate trihydrate.


Data Table 6

Uncertainties from the experiment
trial 1


Mass of the anhydrous Copper
Sulfate (CuSO4) (g)

Mass of Evaporated Water (H2O) (g)





Percentage Uncertainty



In the progress of lab, the experimenter collected
quantitative and qualitative data for accurate and successful lab. Starting
with the Data table 1, which is a quantitative demonstration of the process of
transforming hydrated crystal, copper sulfate into an anhydrous compound by the
relocation of the of water. The successful result of this lab is signify by the
certain compound of copper sulfate attaining to the mass after the heating of
the salt and the changing of its appearance as it is explained above on the
qualitative data. The mass of the constant mass is displayed after the first,
which is 24.5 gram.


Going through the next step, the removal of the water
molecules from Data Table 2 shows the mass of the evaporated water or in a
different term, the mass of the water molecule in copper sulfate. Respectively,
the mass of the water molecule comprising in the copper sulfate is 0.7.

Eventually, the copper sulfate hydrate will become an anhydrous cupric sulfate
with the collected data of mass, which is 2.00 gram. In addition, for more
precise result both Data Table 3 and 4 displays the uncertainties of the entire
process. Furthermore, with the mass of the water and anhydrous copper sulfate
calculated the further calculation would make the units convert from grams to
moles.  The above data table 3 and 4
shows the calculation of the mole that there is 0.0389 mole of water, upon the
removal of water resulting 0.01253 mole of anhydrous copper sulfate. Thus, the
calculation revels the mole ratio of anhydrous copper sulfate and water
molecule indicating 1:3 that means that for every one mole of copper sulfate
there are three existing water molecules.


As progressing the scientific lab, there always was existing
uncertainty. The experimenter recorded each data table with uncertainties and
summarized clean organized uncertainties above all in Data Table 6. The data
table tells the process of converting copper sulfate to an anhydrous cupric
sulfate hydrate containing with 20% and 20% uncertainty percentage of anhydrous
copper sulfate and Evaporated Water.



The uncertainty value of gram
from the scale used to measure the masses of crucible, and copper sulfate,
there could have made a systematic error in this investigation, nevertheless,
the absolute uncertainty and the percentage uncertainty values are still state
in data table 3 and 4. In order of using uncertainty value of grams,
the equipment that have been scale used in the investigation can be resulted
and make it more accurate.


Moreover, as the experiment was done only once which makes
the lab was hard to succeed with a proper result. By one trial the outcome have
resulted a total of at least three portions of copper sulfate hydrate being
investigated, which will definitely aid in the accuracy of the results that
have been collected. The additional trials will not only narrower data spread,
hence the precision of the data, it would lower the uncertainty of 20% and 20%
as shown in data table 6.


The percentage uncertainty of 25.18% from the mass of
Evaporated Water and 10% from anhydrous Copper Sulfate concluding a existence
of a quite large potential of error in the experiment with an associating
uncertainty value of 35%.  The combined
uncertainty value of 35% come up with the calculation of mole ratio of the
anhydrous cupric sulfate and water molecules. This means that, given accuracy
of the scale, the ratio of 1:3 calculated based on the mass obtained on this
non-electronic scale is only at the level close to theoretical value, 44% uncertainty.


According to the data collected, the experimenter deduced
that the compound that has been investigated is Copper Sulfate Trihydrate, with
a chemical formula of CuSO45H2O. The chemical formulas illustrates that for
every one mole of copper sulfate, three moles of water molecules should be
removed as evaporated and leave one mole of copper sulfate which makes an anhydrous
cupric sulfate.



Formula of Hydrate (thanks to Adam Hildebrandt C11-3-11)