

Experiment
1

Weighing
Overview
The ability to read the numerical scale of a measuring
device will be very important to you in your study of chemistry and
other sciences. This experiment, although framed in terms of
determining the mass of some small "unknown" objects, is really an
exercise in significant figures and how to read an analog scale
correctly, to the limits of precision permitted by the scale.
Generally, we read the scale of any measuring device to onetenth
(0.1) unit of the smallest marked scale division.
Calculations



Trial 1

Trial 2

Trial 3

10.143 g 
10.115 g 
10.124 g 



The mean mass of the unknown is then the sum of the individual
measurements, divided by the number of measurements (i.e., three).
Calculate the mean mass of the three measurements of mass above.
Then click
here to see if you did the calculation correctly.
The deviations of the individual results from the mean
result are then calculated as follows: subtract the mean from each
of the individual masses determined. Using the individual masses for
the three trials above, and the mean mass you calculated, calculate
the deviations from the mean for each trial. Then click
here to
see if you did the calculation correctly.
The average deviation, is then the sum of the absolute
values of the individual deviations, divided by the number of
measurements (three). For the three individual deviations you
calculated above, calculate the average deviation. Then click
here to
see if you did the calculation correctly.
Another means of expressing the precision of a measurement is in
terms of the percent deviation. For the data above, the
percent deviation would be given by
Such a small percent deviation shows that the three measurements
of mass were relatively consistent with one another.
If you are still having trouble with this report after having
worked through and studied the examples on these pages, please see a
tutor at the Freshman Lab Help Center (OH223b) as soon as possible.
