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The Synthesis of Alum Lab

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Michaela Tonsager

on 2 June 2014

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Transcript of The Synthesis of Alum Lab

The Synthesis of Alum Lab
Michaela Tonsager and Kaili Johnson
To perform different tests to determine if the substance is actually alum
First, we synthesized a sample of alum. We mixed 1 gram of aluminum foil with 25 mL of KOH solution. We then filtered the mixture through the funnel and flask setup.
We then added sulfuric acid and gently boiled the mixture. We collected our crystals by pouring the mixture through the filter-flask setup again with vacuum filtration and took the mass of our crystals.
Part A Procedure Continued
We pulverized dry alum and put it in a tube. We put the tube in a water bath with a temperature probe and waited until the powder became clear. We then wrote down that temperature.
Part B Procedure
We put our alum crystals in the crucible and gently heated it. We then measured and recording the mass after it had been heated, and after it had dried overnight.
Part B Procedure Continued
We measured one gram of our alum sample into a beaker and added 50 mL of distilled water. We then added 2.062 g of Ba(SO4). We then put the tube in a centrifuge to separate out the liquid.
Part B Procedure Cont.
1. Theoretical Yield: 1 g Al x (1 mol. Al/26.98 g Al) x (1. mol KAl(SO4)2 x 12 H2O/ 1 mol. Al x 474.46 g= 17.59
2. Percent Yield: 15.835/17.59= 90.02%
3. The amount of aluminum foil, if all ions were filtered during filtration
7. The crystals were small and white. They stuck together to form a little bit bigger white chunks

Part B:
1. Yes, our melting temperature was 99.4 degrees C and the published melting temperature of alum is 92.5 degrees C. Our calculated percent sulfate was 42.44%, which was close to the theoretical prediction of 40.5%. We calculated 10.593 H2O molecules, when theoretically, alum has 12 H2O molecules. Our tests overall were fairly accurate, our closest being the percent sulfate.
2. Other tests that we could perform would be to use the percent sulfate in the alum and find its mole ratio to figure out how much water is in the alum.
3. We would not be very confident because, although our temperature was fairly close, it was not spot on. Also, other compounds could have similar melting temperatures.
5. When complex chemical compounds are formed from smaller ones.
6. By adding heat to the solution, crystals were formed, which decreased solubility.
Determining the percent sulfate

Determining the number of water molecules
We determined that our sample was in fact alum. Our melting point of 99.4 degrees C was similar to the published melting point of 92.5 degrees C. Our percent sulfate was 42.44%, which is close to the theoretical value of 40.5%. Also, we calculated, from our data, that there were 10.593 H2O molecules, which is fairly close to the 12 molecules that there are supposed to be.
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