Percentage Composition of a Mixture

Discussion
In this lab you will be given a mixture of either sodium or potassium chlorate and an inert material like sodium chloride. Your task will be to determine the percentage of the chlorate compound in the mixture. This can be accomplished by heating a sample of the mixture to decompose it and comparing the amount of oxygen produced to the theoretical percentage of oxygen present in the compound. YOU MUST BE VERY CAREFUL WHEN HEATING CHLORATES AS THEY BECOME EXPLOSIVE WHEN CONTAMINATED WITH ORGANIC MATERIAL. KEEP EVERYTHING CLEAN AND WEAR PROTECTIVE EYEWARE. FOLLOW THE DIRECTIONS OF YOUR INSTRUCTOR.

Procedure
1. Mass a clean, dry, empty test tube to the nearest milligram and record in your data table.
2. Mass out approximately 4 grams of the mixture on one of the triple beam balances.
3. Place the mixture into the massed test tube, determine the combined mass of the test tube and potassium chlorate to the nearest milligram and record in your data table. (The amount of mixture 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.

Questions
1. From the formula of the chlorate present in your mixture calculate the theoretical percentage of oxygen present in the chlorate.
2. Determine the mass of oxygen liberated.
3. Using answer to questions 2 and the balanced equation, determine the amount of potassium chlorate present in the mixture.
4. Calculate the percentage of the chlorate compound present in the mixture.


Teacher Comments
This document has been enhanced for Netscape 2.0.

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

This laboratory exercise is a nice lab to do as a follow-up to Percentage Composition of a Compound.


 
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