Introduction:
In this lab students
will use the thermal decomposition of potassium chlorate as a means of determining the percentage composition by mass of oxygen
in potassium chlorate. Students will mass a empty crucible, mass it again with a sample of potassium chlorate, and the heat
the crucible and contents, gently at first, with a Bunsen burner until all of the oxygen has been driven off. Once the crucible
and contents are cool, they can be massed and the percent oxygen can be determined.
It is a good idea
before doing this lab to go over the proper lighting techniques and rules for Bunsen burner use. As well, before beginning
this lab, the idea of experimental and percentage errors should be discussed and their formulae given.
Estimated time to complete lab:
50-60 minutes should be plenty of time to complete the lab, clean up, and perform the necessary calculations.
Equipment Required:
For each group:
- Crucible
- Scoopula
- Bunsen burner
- Iron ring and stand
- Clay triangle
- Balance
- Crucible tongs
Safety Concerns:
- Wear safety glasses at ALL times during the lab.
- Students will be working with Bunsen burners, so all of the usual precautions for working with
Bunsen burners should be followed.
- Students can not leave an operating Bunsen burner unattended.
- Remind the students that the crucible, iron ring, and clay triangle will be HOT for a long time after the burner is
shut off. Burnt fingers are common among impatient students.
- Be sure to wash hands after using.
Clean Up Concerns:
Be sure that all equipment is
cool before putting it away. The potassium chloride produced can safety be placed in a garbage can or washed down the sink
with running water.
What Can Go Wrong:
- If the students heat the crucible and contents too strongly initially, some of the potassium chlorate can ‘spit’
out of the crucible and land on the lab bench or the students’ hands – they don’t like this.
- The potassium chlorate melts, foams, and then solidifies during the heating process. It is important that the students
do not allow the liquid to boil over the crucible of they will have to start again from the beginning.
- In the calculations, the students often get confused
as to which mass belongs to the oxygen and which belongs to the potassium chloride.
Student Lab Sheet as a Word Document:
click here to download file
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