The Glass Bead Lab: Report Tutorial
Palko (1-29-04)
Each report should begin with a heading that includes the title of the experiment, the
name of the person who is submitting the report and the date it was turned in. To
complete this, fill in the blanks above.
Purpose:
This section is usually just a few sentences. The idea is to succinctly state the reasons for
doing the lab. This can include learning goals (practice measurement techniques) and
specific experimental goals (determine the density of glass beads). DO NOT repeat the
purpose written in the lab handout, you should distill this section down and write it in
your own words. This has already been done for you as an example for future reports and
a future tutorial will explain in detail how these are to be written.
Procedure:
Formation of Groups
For this part of the report, list members of your group and describe the exact roles they
played during the experiment. In other words, in all lab reports, you should describe
briefly what each person did to help the group to carry out the procedure. This should
already be recorded in your lab notebook on the day of the experiment so you only need
to rewrite it in the final report.
Part I: Determining the Density of a Single Glass Bead
In this part or the report you should briefly summarize the experimental procedure your
group agreed on to measure the volume of a single glass bead. The rest of the procedure
was explicitly described in the lab handout and does not need to be repeated. This is true
of all future lab reports. You should only include an explanation of the procedures that
the group decided to use that was not specifically described in the lab manual. A
summary of the procedure should have been recorded in your notebook during the lab
and only needs to be rewritten in your final report.
Data and Results For Part II: Determination of the Density of a Glass Bead
Mass Diameter Radius Volume
Density
Deviation from
(g)
(cm)
(cm)
(cm3 or
(g/mL)
Avg.
mL)*
Bead #1
Bead #2
Bead #3
Average
1 cm3 = 1 mL
1. Example calculation of radius and volume for one of the beads in the Table for
Part II.
2. Example calculation of density (mass/volume) for one of the beads in the Table for
Part II.
3. Example calculation of the deviation between the density for one sample and the
average in the Table for part II.
Data and results should always be tabulated with the quantities being measured or
calculated as column headings and the identity of each sample as row headings. There
should also be a title for the table that describes what data is shown by the table. In the
heading of each column and row the units of measurement are included so that you do
NOT need to record the units after each number. All numbers should be recorded in the
table with the correct number of significant figures based on the stated precision of each
measuring device. Even if the measured value is zero, it should be recorded with the
same precision as all the other nonzero measurements made with the same device.
In some cases as in the table above, both data and results are combined into a single
table. In some experiments it will be more convenient to separate them. Also notice that
an average value is placed on a separate line below the table since it is not related to one
particular sample. Other footnotes explaining the data and results can be included, such
as example calculations. You should provide a set of sample calculations for each column
of results included in the table and you should use the correct number of significant
figures for each calculated value.
Data and Results For Part II: Determination of the Density of a Set of Glass Beads
Mass (g) Initial
Final
Net
Density
Deviation
Volume Volume Volume (g/mL)
from Avg.
(mL)
(mL)
(mL)
Sample #1
Sample #2
Sample #3
Average
1. Example calculation of volume for one sample in the Table for Part II:
2. Example calculation of density (mass/volume) for one sample in the Table for Part II:
3. Example calculation of the average deviation between the density for one sample and
the average density in the Table for part II:
Conclusions
First you should always have a simple conclusion statement that summarizes or restates
the final results and explains how the results obtained fulfills the purpose of the
experiment. Notice that a purpose of this experiment was to determine the density of glass
beads. Were you successful in determining the density of the glass beads? Explain your
answer. As a second part of the conclusion section you will need to use the precision of
the data to determine how much variability there is within each set of data and results.
One final note: how do you know if your results are accurate? In order to determine
accuracy, you need a reference value for the density of glass. This can be obtained from a
reference book such as the CRC Handbook of Chemistry and Physics; Lange’s Handbook
of Chemistry, the Merck Index, your textbook or may be provided by your instructor. If
you are provided with a reference value for the density of the glass beads this experiment,
restate the two average densities you obtained and compare the reference value to your
averages from Part I and II. To make this comparison determine, in each case, if your
average value is higher or lower and by how much it differs from the reference value.
You could also calculate the percent difference, which is defined as:
% Difference = [(calculated or measured value - reference value)/reference value]*100
The sign of the percent difference indicates whether the calculated or measured value is
larger (positive) or smaller (negative) than the reference value. If you are not provided
with a reference value all you should do is restate the final calculated results.
Compare the data you collected with another group that used a different size bead. What
effect did using larger beads have?
The Determination of the Density of Glass Beads
Background:
Physical properties such as density can be used to characterize a specific type of matter,
in this case, glass beads. The determination of density involves making measurements
that will provide mass and volume data regarding the beads. It is possible to collect this
data in a number of ways. You will use two methods of collecting the necessary data and
then compare those methods in terms of precision and accuracy.
Precision describes the degree of certainty in your results. It can be looked at two ways.
For an individual measurement, precision is represented by the degree of guessing used to
make that measurement. For example, if you were to measure the width of this page, you
might obtain a result of 21.50 cm. The last digit of this measurement is a guess because
the ruler used was marked every 0.1 cm. We guess the last digit as it represents a value
that is not marked on the ruler, but can be estimated. We could represent the “degree of
guessing in this measurement as +0.01 cm. We can calculate the relative “degree of
guessing” by comparing the guess amount to the actual measurement.
Relative guess = degree of guessing/measurement value x 100
In this case, +0.01/21.50 x 100 = 0.05 %
If the actual measured value were smaller, then the relative guess would become larger.
In other words, our guessing becomes a more significant factor as the size of the object
being measured becomes smaller.
Accuracy is a comparison of the experimental result to some “accepted” or “real” value.
The conclusion section of the report tutorial details a calculation that allows for a
numerical comparison. In general, if there is a value available for comparison, it is
prudent to compare experimental results to this and discuss any possible reasons for
differences.
Purpose:
1. Measure mass and volume of a single glass bead and calculate its density.
2. Measure the mass and volume of a set of glass beads and calculate density of the
beads.
3. Devise a method to determine volume of a glass bead.
4. Evaluate your results.
Procedure:
Work in a group of three or four.
Part One:
Meet as a team and determine a method to determine the volume of a single glass bead.
Each team member should then obtain a bead and use that method to determine the beads
volume. Additionally, each team member needs to obtain the mass of his or her bead.
Share all individual data and record it in the table on the report sheet for part I.
Part Two:
In this part, you will work as a team to determine the volume and mass of a set of beads.
Obtain a beaker of beads. Divide this sample into three parts of varying size. Obtain the
mass of each part. Use water displacement to determine the volume of each part. To do
this, obtain a graduated cylinder and half fill it with water. After recording this volume,
add the beads and record the new volume. Calculate the bead’s volume by taking the
difference of the two volume measurements.
Calculations:
Complete all calculations as directed on the report sheet.
Important relationships:
Diameter = 2 x (radius)
Volume of a sphere = 4/3 x () x (radius)3
Density = mass / volume
Deviation from average = Average value of all trials – value from single trial
Note:  = 3.1415 or can be obtained from a button on your calculator.