Name: _________________________________ Section: _____________________
Chemistry M12 Laboratory Manual Page 27
Experiment 6 – Decomposition of Potassium Chlorate
Discussion
The percentage composition of a compound is the percent by mass of each element in the
compound. This can be theoretically calculated using atomic masses found on the periodic
table, and experimentally calculated from lab data. The percent composition is calculated by
taking the mass of the part divided by the mass of the whole times 100.
In this experiment, solid potassium chlorate will be strongly heated. This causes it to
decompose into solid potassium chloride and oxygen gas. The relative amount of potassium
chloride (residue left behind) and oxygen gas (mass lost) are experimentally measured and
compared to the theoretical values.
Percent error is calculated by finding the absolute value of the difference between the
theoretical and experimental values and dividing that number by the “true” theoretical value
and last multiplying the answer by 100.
Following the quantitative test, we will perform a qualitative test on the residue and known
compounds of KClO3 and KCl using silver nitrate solution. AgNO3 solution is used as a general
test for chloride ions. A positive test forms white solid AgCl and indicates the presence of Cl–
ions in a solution. Tap water contains chloride ions, so it is very important to perform this test
with clean equipment that has been rinsed out with deionized water and to use deionized water
in the test.
To obtain accurate and precise data you should do the following:
1. Use the same balance for all mass measurements.
2. Record data directly and immediately into the lab report.
3. Record data completely (to the nearest 0.001 g); do not round off the data.
4. If an error is made in data collection, do not scratch out or erase but simply draw a
single line through the error and write the correction beside it.
5. Duplicate samples should be analyzed so that results can be compared and averaged.
6. Handle the crucibles with tongs not fingers.
7. The crucible must be covered while heating to avoid any loss due to splatter.
