Experiment 5: Percentage of Oxygen in Kclo: (S) 2 KCL (S) + 3O (G)
Experiment 5: Percentage of Oxygen in Kclo: (S) 2 KCL (S) + 3O (G)
Experiment 5: Percentage of Oxygen in Kclo: (S) 2 KCL (S) + 3O (G)
Introduction: In this experiment you will determine the percentage of oxygen in potassium
chlorate. You will calculate the theoretical value from the chemical formula and compare your
experimental value to the theoretical value.
Materials Needed
Equipment Chemicals
Iron ring, clay triangle, Crucible tongs Potassium Chlorate, KClO3
crucible & cover or Pyrex test tube Manganese dioxide (optional catalyst)
Cooling pad
Crucible Method:
Weigh a clean dry crucible and cover. Optional, add 0.50 g MnO2 catalyst. Next, obtain a
sample of potassium chlorate, KClO3, as directed by your instructor. Place about 1.5 g of
KClO3 in the weighed crucible, and reweigh. Remember to use the same balance for all
weighings of the same sample. Mix the catalyst well if using the MnO2.
Place the crucible with KClO3 on a clay triangle and set the cover slightly ajar, see figure 1.
Very gently heat the crucible containing the powders for about 8 minutes, then heat strongly
for 10 minutes. Be sure the inner-blue cone of the flame is just below the crucible bottom
while you are heating strongly, and that the crucible bottom and/or clay triangle are heated to
redness. Allow the crucible to cool to room temperature, which takes at least 10 minutes, and
then weigh the crucible and residue. Record your data in your lab notebook.
Heat strongly for a second time for about 5 minutes, then cool and weigh. If the weighings
after the first and the second heatings are not the same, i.e. they differ by more than 0.02 g;
repeat the process of heating and cooling and weighing as needed, until 2 successive weights
agree (within +/- 0.02 g). Calculate the experimental percentage of oxygen in KClO3 based
on the final weight of container’s contents.
Add about 1.0 to 1.5 g of potassium chlorate, KClO3, to the test tube. Record the mass of the
container and its contents. Mix the contents of the test tube until they have a somewhat
uniform gray appearance. (Be careful not to lose any of the contents.) Carefully heat the test tube
and its contents, see fig 2 below. Heat gently at first, increasing the intensity after the mixture
seems to "boil," as it sometimes appears to do when bubbles of oxygen are being released.
Continue heating for about five minutes, and then cool and weigh. Repeat the process in 5-
minute heating cycles until constant mass is reached. Set the container and its contents aside
while you complete your calculations. Do not discard the residue until your calculations are
finished and satisfactory; if they are not satisfactory, it is possible that you may be able to
salvage your work if the material is still on hand.
Safety: Potassium chlorate is a strong oxidizing agent. It may cause fires or explosions if
mixed or heated with combustible materials such as paper. This experiment is
Potentially hazardous, and if performed carelessly could lead to a serious accident!
The formation of a gas at the bottom of a test tube may result in a sudden expansion,
blowing hot chemicals out of the test tube. This will not occur if the test tube is handled
properly during heating. When heating a solid in a test tube, tip the tube until it is almost
horizontal and tap it carefully until the contents are distributed over the lower half of the
length of the tube, as shown in Figure 2. Holding it at about this angle, move the test
tube back and forth in the flame of the burner, distributing the heat over the entire length
of the mixture. Do not concentrate the heat in any one area, particularly near the
bottom of the test tube.
Be very sure your test tube is not pointing toward anyone, including yourself, while
it is being heated. Be aware of your surrounding while doing this experiment. Do not
place yourself in front of somebody else's test tube. Wearing goggles is
absolutely.
Waste Disposal: Excess or spilled potassium chlorate and the residue (KCl) should be
placed in labeled waste containers in the hood.
a. LiClO3
b. Al(ClO3)3
3. A sample of an unknown metal chlorate, weighing 1.725 g, is heated until all of the oxygen is
driven off. The residue remaining in the container weighs 0.859 g. Calculate the percentage
of oxygen in this metal chlorate.
4. A student records the following data in a laboratory experiment to determine the percentage
of oxygen in Ca(ClO3)2.