Composition of a Compound

Potassium chlorate is one of several compounds of oxygen that are easily decomposed by heating. Potassium chlorate will decompose into oxygen and potassium chloride. In this laboratory exercise you will decompose this compound by heating, and from the data obtained determine the percentage of oxygen by weight in the compound. YOU MUST BE VERY CAREFUL WHEN HEATING POTASSIUM CHLORATE AS IT BECOMES EXPLOSIVE WHEN CONTAMINATED WITH ORGANIC MATERIAL. KEEP EVERYTHING CLEAN AND WEAR PROTECTIVE EYEWARE.

1. Mass a clean, dry, empty test tube to the nearest milligram on the electronic balances and record in your data table.
2. Mass out approximately 2 grams of potassium chlorate on one of the triple beam balances.
3. Place the potassium chlorate into the massed test tube, determine the combined mass of the test tube and potassium chlorate to the nearest milligram on the electronic balances and record in your data table. (The amount of potassium chlorate present is the difference between the empty test tube and the mass of the test tube plus mixture.)
4. Support the test tube with a pole and clamp and begin heating. Heat gently at first and keep increasing the temperature as the bubbling (evolution of oxygen) begins to subside. When you have increased the temperature of the flame to maximum, continue heating until all bubbling has stopped. When decomposition is complete, stop heating, cool and determine the mass of the test tube and its contents to the nearest milligram and record in your data table.
5. Heat the test tube and its contents strongly again for 3 minutes. Cool the test tube and mass again. If this mass does not agree with the mass in step 4 to within 0.01 grams repeat this step until the final two massings agree. This is called heating to a constant mass and is necessary to insure that the potassium chlorate has completely decomposed. The last mass recorded is the most important. However, you should always record all massings in your data table.

1. Write a balanced formula equation for the decomposition reaction that took place.
2. Determine the mass of oxygen liberated.
3. Calculate the percentage of oxygen in potassium chlorate from the data collected.
4. Calculate the theoretical value for the percentage of oxygen in potassium chlorate.
5. Determine the relative error of your procedure.
6. Assume that a geologist had located three iron mines: one containing FeO, one containing Fe2O3, and one containing Fe3O4. Assuming the cost of mining was the same in each case which of these mines would yield the greatest amount of iron per ton of ore mined?

Teacher Comments
This document has been enhanced for Netscape 2.0.

Students need to be instructed in the proper use of chlorate compounds!!

Percentage Composition of Mixture is a nice laboratory exercise to use as a follow-up to this one. Student's will get a chance to apply the information gathered in this lab.

Questions? Comments??