Umair and Zubair Khan
9-16-11
Block 1
Title: Alum Synthesis Lab Report
Introduction/Purpose: Among the several purposes of this lab were:
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Synthesize Alum from Aluminum so that the Alum crystals can be tested to verify how pure the
compositions and properties of the experimental alum are compared to theoretical values.
To get familiar with accurate methods of weighing, gravity and vacuum filtration, and
crystallization.
To become familiar with the use of laboratory equipment such as beakers, Test tubes,
Erlenmeyer flasks, Hot Plates, Burets, Buchner Apparatuses, Capillary Tubes, Thermometer,etc.
To practice Stochiometry to determine the percent yield of alum synthesized from aluminum
Procedure Part 1:
Synthesizing Alum- Weigh .45-.50 g Al foil on a balance and record the mass +/- .01g. Under the fume
hood pour 13.0 ml of 3.0 M KOH into the reaction beaker. Use a glass rod to gradually mix in the
Aluminum foil with the KOH and observe the reaction. Note down your observations
Gravity Filtration-Place a funnel over a beaker and place a 7-cm piece of filter paper in a cone shape in
the funnel. Moisten the funnel paper with 2-3 mL of distilled water so that it adheres to the funnel. Spill
the reaction beaker contents onto the filter paper in the funnel. Collect and save the liquid filtrate that
filters into the new beaker. Rinse any remaining residue into the filtrate beaker and proceed to discard
the filter paper and its contents in the trash.
Forming Alum: Gradually stir 22.5 mL of 4 M H2SO4 into the filtrate beaker in 5 ml portions; remember to
record any observed changes to the filtrate. Heat this new solution on a hot plate until all the solid
dissolves into a homogenous solution.
Crystallization- Using your tongs, place the filtrate beaker on a wire gauze on your ring stand and allow it
to cool. Prepare an ice bath using 400 mL beaker. After 2 minutes place the Filtrate beaker into the ice
bath. After this, place 3 mL of 95% ethanol into a test tube, and put the test tube in a second ice bath.
Let the filtrate beaker cool in the ice bath for about 20-25 minutes. Crystals should form within 30
minutes of being place in the ice bath.
Vacuum Filtration- Connect a Buchner apparatus to the sink nozzle with a hose. Turn the water on to
begin the vacuum (Water Aspirator). Determine the mass of a filter paper and then place the paper flat
in the Buchner funnel moistening it with 2-3 mL of distilled water. After all crystals have stopped
forming ( may have to wait overnight) then transfer all the crystals into the Buchner funnel onto the
filter paper. Use a rubber policeman on the end of your stirring rod to facilitate the transfer of your
crystals as well as 1-2 mL of your cooled ethanol to help transfer your crystals to the Buchner. Once you
have finished draining all the excess liquid from your crystallized solution into the Buchner then you may
turn off the aspirator( turn off water and disconnect hose). Remove the filter paper with the crystals and
store them in a beaker or petri dish to dry overnight. The next day you will measure the mass of the air
dried crystals subtracted from the mass of the filter paper.
Umair and Zubair Khan
9-16-11
Block 1
Observations during the procedure:
We started the lab with .50 grams of Aluminum foil
As we combined the 13.0 mL of 3.0 M KOH with the Aluminum foil, we noted the reaction to look dark
gray, mildly vaporous, and bubbling.
Grams of Aluminum Foil used in Synthesis
Reaction Observations of Foil with 12.85mL 3.0 M
KOH under the fume hood
Observations upon adding the 22.5 mL of 4 M
H2SO4 to the filtrate in 5-mL portions
Upon Heating & Stirring the Solution on a Hot
Plate
.50 g
Gray, Mildly Vapourous Liquid, Bubbling,
-the filtrate becomes cloudy white upon contact
and the white substance stays afloat in the
solution much like the way a lava lamp acts
-Upon stirring the solution feels more viscous and
turns a solid white color
- As the heating progresses it obviously gets
warmer and there are very light fumes being given
off
Results of Synthesis:
Our theoretical yield of alum should have been .50 g Alum Mol Alum
26.98 g Al
1mol alum
1 mol Al
474.32 g Alum
1 mol Alum
Theoretical Yield of Alum= 8.79 g Alum.
Our Experimental Yield of Alum= 7.35 g Alum
Percent Yield of Alum= [ 7.35 g/8.79 g] x 100 = 83.6%
Procedure Part 2: The purpose of this part of the lab is to analyze the qualities of the synthesized Alum.
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Melting Point Test: Use a Mortar and Pestle to Pulverize about .5g of dry alum (Our group used
about .48 g of our Alum) and pack the pulverized alum into a capillary tube until the alum in the
tube Is about 1 cm deep. Fasten the Capillary Tube to a thermometer next to the bulb of the
thermometer with a rubber band and put the thermometer into a beacker of hot water that is
not boiling. Observe the temperature at which the Alum in the Capillary Tube becomes clear
(melting point) and record it:
Experimental Melting Point of Alum was 88.5*C compared to the Theoretical Melting Point of 92.5*C.
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Amount of Hydrate present in the Alum Crystals: Heat a Crucible and Cover over a Bunsen
burner until it is red hot in order to measure the most accurate mass after they have cooled for
about 10 minutes. Add about 2 grams of Crystals to the Crucible (Our group added about 1.99 g
Umair and Zubair Khan
9-16-11
Block 1
of crystals to our crucible and cover. The mass of our crucible and cover by itself was 19.92 g.
Total= 21.91 g)
Set the Alum in the Crucible on a triangle held in a ring stand while covering the crucible with
the cover loosely. Begin to heat over the Bunsen burner gently until the water vapor ( Hydrate)
is driven off and only the melted anhydrous alum remains( be careful not to burn excessively so
as to drive off some of the alum). After the water vapor has been driven off, let the crucible and
cover cool for 4-5 minutes. Then take the mass again and subtract the new mass from the first.
This will give you the mass of the Hydrate driven off.
21.91 g – 21.00 g = .91 grams of Hydrate
21.00 g – 19.92 g = 1.08 grams of Alum
.91 g/18 g= mol H2O =.05g
1.08 g/ 258 g= mol alum= .004g
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KAl(SO4)2 * 12H2O
Percent of Sulfate present in the compound
Use a balance to weigh 1 g of alum into a 250-mL beaker. Dissolve in approximately 50 mL of
distilled water. Using Stoichiometry Calculate the volume of .2 M barium nitrate which would be
needed to precipitate all of the sulfate ions in solution , and then add twice this amount.
.2 mol/liter* X liters= .00775 L or 77.5 mL.
Filter Paper= .71 g
Cover the beacker after adding 77.5 mL of Barium Nitrate with a watch glass and heat the
solution nearly to boiling . Keep the solution under boiling point for nearly 15 minutes . The
particles will grow in size and will be easier to filter. Filter the Solution onto filter paper and let
dry over night and then mass it.
Mass of Filter Paper after= 2.64 g
2.64g- .71g (fp)=1.93 g Sulfate