Stoichiometry and Analysis
A mixture of KClO3 and some other non-volatile, stable substance can be determined by heating
the mixture to decompose the KClO3 and drive off oxygen, leaving a residue. The loss in weight
is related only to the KClO3 in the original sample. To increase the rate of decomposition, some
MnO2 is added as a catalyst.
Procedure A: Degradation of KClO3
It is first necessary to study the stoichiometry of pure KClO3. To a clean, dry, small test tube,
add about 0.1 g of MnO2. This mass is about the size of a pea. Place a small beaker on the
analytical balance and zero the balance. Place the test tube containing the catalyst in the beaker
and weight to the nearest 0.001 g. The stockroom assistant will add about 1 gram of pure
KClO3. Reweigh the test tube. Calculate the mass of KClO3 that was added. Loosely clamp the
test tube in an inclined position near the top of the tube. Heat the mixture gently. Gradually
increase the heat and rotate the tube to heat evenly. Use moderately strong heat for about 2
minutes after the bubble action has stopped but do not melt the tube. Let the tube cool, weigh,
and heat again for about 2 minutes. If the difference in weight between the first and second
heatings is more than 10 mg, heat it a third time. From this data, calculate the following:
1. Mass of oxygen lost
2. Mass of KCl residue
3. Number of moles of oxygen lost
4. Moles of KCl residue
5. Moles of oxygen per mole KCl
Write a balanced equation for the degradation of KClO3 based on your data.
Procedure B: Unknown Sample
Add about 0.1 g MnO2 to a clean, dry test tube and weigh to the nearest 0.001 g. Obtain from
the instructor an unknown mixture in this tube and reweigh. Tap to mix and heat as in procedure
A. Tabulate all data and calculate the following:
1. Mass of the mixture
2. Mass of Oxygen lost
3. Moles of oxygen lost
4. Moles of KClO3 in the original sample (use your balanced equation from
procedure A)
5. Mass of KClO3 in the original sample
6. Percentage of KClO3 in the original sample.
Report
Using the data recorded in your notebook, write up a report for procedures A and B in Microsoft
Excel. Use Excel formulas to redo the calculations performed in lab. Apply number formatting
so Excel shows the correct number of significant figures.
Submit the report by Email to aherbelin@lcc.ctc.edu including CH151 in the subject line.
Created by aherbelin
116102779
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2/12/2016
Name
___________________
Lab Section ___________________
Pre-Lab Exercises
1. Find definitions for the following terms: volatile, non-volatile, catalyst, residue,
decomposition. Use a combination of a dictionary, the chemistry textbook, and possibly the
internet. Several dictionaries are available online.
2. Kelsonium, atomic weight 80, forms an oxide KeO. A 0.384 g sample of this oxide will
combine with more oxygen to form another oxide weighing 0.512 g. What is the formula for
this oxide? Show your work.
3. Sodium nitrate, upon heating, is converted to sodium nitrite, NaNO2. A mixture of NaNO3
and NaNO2 weighing 1.508 g. loses 0.128 g of oxygen when heated to constant weight.
Calculate the percentage of pure NaNO3 in the mixture. Show your work.
Created by aherbelin
116102779
Page 2/2
2/12/2016