Procedure for EXPERIMENT 1
Gather the digital scale, 2 oz. aluminum cup, glass stirring rod, and cotton ball.
The aluminum cup is composed primarily of elemental aluminum, Al. Use the periodic table in Figure 1 of the background to identify the molar mass of this element. Download a printable version of the Periodic Table.
Note: The aluminum cup is covered by a thin layer al aluminum oxide, Al2O3, but this compound accounts for less than 0.1% of the mass of the cup.
Record the molar mass in Data Table 1.
Turn on the digital scale and ensure that it displays 0.00 g.
Place the aluminum cup on the scale and determine its mass. Record the mass of the aluminum cup in Data Table 1.
Calculate each of the following and record your findings in Data Table 1.
Number of moles of Al present in the aluminum cup.
Number of atoms of Al present in the aluminum cup.
The glass stirring rod is composed primarily of silicon dioxide, SiO2. Use the periodic table to determine the molar mass of this compound and record in Data Table 1.
Note: Glass is composed of additional compounds such as sodium oxide, sodium carbonate, and calcium oxide. For the purpose of this exercise, it will be assumed your sample contains only silicon dioxide.
Place the glass stirring rod on the scale and determine its mass. Record the mass in Data Table 1.
Calculate each of the following and record your findings in Data Table 1.
Number of moles of SiO2 present in the glass stirring rod.
Number of moles of Si and O present in the glass stirring rod.
Number of atoms of Si and O present in the glass stirring rod.
The cotton ball is composed primarily of cellulose, a polymer of glucose, C6H10O5. Use the periodic table to determine the molar mass of this compound and record in Data Table 1.
Note: Cellulose is a complex carbohydrate consisting of 3,000 or more glucose (C6H10O5) units. For the purpose of this exercise, it will be assumed your cotton ball consists of simple glucose molecules.
Repeat steps 8-9 for the cotton ball.
Procedure for EXPERIMENT 2
Exercise 2 Water of Hydration
In this exercise, you will determine the chemical formula of a hydrated potassium aluminum sulfate sample (alum).
Procedure
Put on the safety goggles and gloves.
Turn on and tare the digital scale so that it reads 0.00 g.
Place the aluminum cup on the scale to obtain the mass and record the mass in Data Table 2.
Using the second aluminum cup as a weigh boat, place the aluminum cup on the scale, tare the scale and measure 2.00 grams of KAl(SO4)2.
Transfer the alum to the first aluminum cup and place the aluminum cup containing the KAl(SO4)2 on the scale to obtain the mass. Record the mass in Data Table 2.
Assemble the burner setup and light the fuel, as shown in Figure 2.
Gather the burner fuel, aluminum pie plate, burner stand, 2 oz. aluminum cup, and lighter or matches.
Place an aluminum pie plate on a solid work surface away from flammable objects.
Set the burner stand towards the back of the pie plate.
Use matches or a lighter to ignite the fuel. BE CAREFUL- the flame may be nearly invisible.
Gently slide the fuel under the stand.
The small, 2 oz. aluminum cup will be placed over the fuel to extinguish the flame. Set the aluminum cup next to the burner setup so you are ready to extinguish the flame at any point.
Figure 2.
Burner fuel setup.
Pick up the aluminum cup containing the KAl(SO4)2 with the test tube clamp, as shown in Figure 3, and place it onto the burner stand, as shown in Figure 4.
Figure 3.
Holding aluminum cup with test tube clamp.
Figure 4.
Aluminum cup on burner stand with heat source.
Note: You will see the water being released from the alum as it bubbles and evaporates off of the sample.
Allow the aluminum cup to heat on the burner for approximately 5 minutes or until all bubbling has ceased and the sample appears dry. See Figure 5.
Figure 5.
Dry sample (KAl(SO4)2) following heating.
After the aluminum cup cools for a few minutes, use the test tube clamp to transfer it to the tared digital scale. Record this mass of the aluminum cup and KAl(SO4)2 in Data Table 2.
Repeat steps 7 through 9 another time, to complete the 2nd heating in Data Table 2.
Note: Step 10 is reheating the same sample, NOT starting with a fresh sample.
Use the other empty 2 oz. aluminum cup to extinguish the burner fuel flame. See Figure 6.
Do not touch the metal stand; it may be hot.
Carefully slide the burner fuel canister out form underneath the burner stand. The sides of the burner fuel canister will be warm, but not hot.
Place the aluminum cup directly over the flame to smother it. The cup should rest on top of the fuel canister, with little or no smoke escaping. Do not disturb the burner stand, allow everything to cool completely.
Once all equipment is completely cool, remove the aluminum cup and place the plastic cap back on the fuel. Ensure that the plastic cap “snaps” into place to prevent fuel leakage and evaporation. The aluminum cup, fuel, and all other equipment may be used in future experiments.
Figure 6.
Extinguishing burner with flame.
Calculate the mass of water released by heating the sample by subtracting the mass of the 2nd heating from the mass of the Aluminum Cup + 2.00 grams of KAl(SO4)2 and record in Data Table 2.
Subtract the water mass from the original hydrate mass of 2.00 g to obtain the mass of anhydrous KAl(SO4)2.
Calculate the molecular mass of H2O and record in Data Table 2.
Calculate the moles of water released by heating the sample and record in Data Table 2.