Sample Lab Report -
Introduction
In this experiment we measured the percent composition of oxygen
in air. The
measurements were made by inverting a graduated cylinder containing
air and acid soaked
steel wool into a beaker containing water. The iron of the steel
wool reacted with the
oxygen to generate rust (iron oxide). The acid served to speed
up the reaction between
the iron and oxygen. As the steel wool reacted with the oxygen
trapped in the graduated
cylinder the volume of gas in the cylinder decreased causing the
water level in the
inverted cylinder to rise. The decrease in the volume of gas in
the cylinder is corresponds
to volume of oxygen present in the cylinder initially. From the
change in the water levels
and the initial volume of air trapped in the cylinder the percentage
of oxygen in air was
calculated.
The procedure was the same as that given in the lab manual, except
three trials were
performed rather than two.
Data:
height of cylinder = 125.5 mm
radius of cylinder = 10 mm
| Trial #1 | Trial #2 | Trial #3 | |
| Initial height of water | 8 mm | 8 mm | 9 mm |
| Final height of water | 14 mm | 25 mm | 29 mm |
| mass of steel wool | 0.75 g | 0.71 g | 0.73 g |
| volume of steel wool | 95.4 mm3 | 90.3 mm3 | 92.8 mm3 |
| volume of air | 3.69x104 mm3 | 3.69x104 mm3 | 3.69x104 mm3 |
| volume of oxygen | 1.88x103 mm3 | 5.34x103 mm3 | 6.28x103 mm3 |
| oxygen percentage of air | 5.1 % | 14.4% | 17.0% |
The average percentage of oxygen in air was determined to be 16%.
Note: data from trial #1 was not used for this calculation. See discussion section of report.
Here you should show calculations for one trial. Include formulas. For instance:
Using data from Trial #2--
Volume of air = pr2h,
where r is the radius of the cylinder and h is the
height of the air column (height of the cylinder - initial height
of water)
Volume of air = p (10 mm)2(125.5
mm - 8 mm)
= 3.69 x 104 mm3
(and so on for each calculation)
We determined the oxygen composition of air to be 16% by volume.
This value is much
lower than the accepted value of 20.6% at sea level. This is an
error of 22% from the
accepted value. We found the first trial did not work properly
and so we did not include
the data from the first trial. (The value of 4.8% O2
from trial #1 was outside the standard
deviation of the average of the three results which indicated
that it was probably not a
valid data point.) In the first trial, our steel wool was tightly
packed in the bottom of the
graduated cylinder, and our TA indicated that this might cause
a problem. Because the
oxygen must react with the steel wool to be ìdetectedî,
the more tightly the wool is
packed the less chance the oxygen has to diffuse to the surface
of the steel wool and react.
Our results indicate that the procedure is not a very accurate
predictor of oxygen content.
Empirical evidence suggests that the oxygen content in the room
was normal (everyone
was breathing normally), but yet we determined the percentage
of oxygen to be 22%
below what it should be. Probably we would have gotten better
results if we allowed the
reactions to go for longer than 30 minutes each. We saw that the
second two trials
produced much more rust on the steel wool than the first trial
which had the densely
packed steel wool. Low values of oxygen in the air are consistent
with incomplete
reaction between the oxygen and the steel wool. The amount to
which the steel wool is
packed seems to have a great impact on the final result, so that
a precise value of the
oxygen content of air would be difficult to determine using this
experimental procedure.
[Answers to questions would go here.]