NAME _______________________________
DATE______________ PERIOD _______
Percent Composition of Oxygen in KClO3
LAB 4
PRELAB INFORMATION
Percent composition is the percent by mass of each element in a compound. The percent composition
includes as many percents as there are elements in the compound. To determine the theoretical percent
composition, one compares the mass of each element present in a one mole sample of the compound.
This can be written:
% element = mass element (g)
molar mass compound (g)
In this laboratory investigation, you will heat potassium chlorate with a catalyst. The result will be the
decomposition of potassium chlorate into potassium chloride and oxygen gas as seen in the balanced
chemical equation:
MnO2 (s)
2KClO3(s)
2KCl(s) + 3O2(g)
PURPOSE
The purpose of this lab is to experimentally determine the percent composition of oxygen in potassium
chlorate and then compare your results to the theoretical value.
HYPOTHESIS – Calculate the theoretical % composition of O in KClO3 (use masses from the periodic table)
Calculation:
PROCEDURE
(follow written procedure; keep a record of the procedure in your lab book, but put it in your own words)
1. Mass an empty, clean dry test tube. Record.
2. Mass 1.00 g of potassium chlorate. Record. (Be sure to use weigh paper.)
3. Add the potassium chlorate to the test tube.
4. Mass 0.50 g of the catalyst manganese dioxide. Record.
5. Add the manganese dioxide to the potassium chlorate in the test tube.
6. Mix the two solids thoroughly by gently tapping the sides of the test tube.
7. Using a test tube holder, tip the test tube and its contents until it is almost horizontal (70o).
Tap it gently until the contents are distributed evenly over the lower wall of the test tube (see
the figure).
8. Holding the test tube at an angle and pointed away from others, move the test tube back and
forth through the flame slowly and continuously, distributing the heat evenly over the entire
length of the contents of the tube. Record your observations.
9. When no further changes to the matter are observed, approximately three minutes, stop
heating and turn off the burner.
10. Let the test tube cool for approximately five minutes. Do not touch the bottom of the tube
because the contents will remain hot for a longer time.
11. Mass the test tube and its contents. Record.
12. Place the waste as directed and clean up your workstation.
OBSERVATIONS/DATA
QUANTITATIVE DATA
Substance/Object
Mass (______)
Test tube
KClO3
MnO2
Test tube + contents after heating
QUALITATIVE DATA
Substance
Observations
KClO3 + MnO2 mixture before heating
Contents of test tube during heating
Contents of test tube after heating
CALCULATIONS
1. Using your data, calculate the mass of KCl produced.
2. Calculate the mass of the oxygen produced by the reaction.
ANALYSIS/CONCLUSIONS
1. Calculate the percent of oxygen in your sample of potassium chlorate. Use data from the lab.
2. Calculate you percent error for the lab by comparing the actual percent of oxygen (hypothesis) to
the experimental value (#3).