Lab 1: Measuring Density
Intensive or Extensive Property?
Purpose
To determine if density is an intensive or extensive property of matter.
To learn laboratory measurement techniques to take measurements correctly
To investigate the error associated with the measurements of volume in the chemistry lab
(check accuracy)
To use significant figures correctly
Background
Intensive properties of a substance are properties that do not change when the amount of
the sample is varied. Extensive properties are properties that change when the amount of
the sample is varied. You will be given a liquid and be asked to determine if density is an
intensive or extensive property.
The density of a substance is the mass of substance per unit volume. It can be found by
dividing the mass of a substance by its volume.
density =
mass of substance
volume of substance
By rearranging we get:
mass of substance = density × volume of substance
If you have a series of data, you can plot the mass vs the volume and the slope of the
resultant graph will give you the density.
450
400
350
Mass (g)
300
250
200
150
100
Slope = Density = 3.5 g cm-3
50
0
0
20
40
60
80
100
120
Volume (cm 3)
Graph 1: Determination of Density of Substance A
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Weighing by difference
Through out this course you will need to do a lot of weighing. To weigh things
accurately, we use the difference method. To weigh the water in this lab take the
following steps:
1. Get a small dry beaker (100 mL)
2. Weigh the beaker on an analytical balance (one that weighs to 0.0001g or 0.1mg)
and record the weight. After you have weighed the beaker, you must not handle it
with your bare hands, as the oils from your hands will cause you to get erroneous
readings.
3. Remove the beaker from the balance and place the water in the beaker
4. Reweigh the beaker on the SAME balance.
There are 3 analytical balances in each room and this method will allow you all to share
the balances efficiently.
When using the balances in the lab, the sample MUST be at room temperature.
Procedure
In doing this experiment, you will need to use pipettes, graduated cylinders, burettes and
balances to determine the volume and mass of the substance. Each member of your
group should have a chance to measure the volume using each piece of glassware.
Groups meeting on Mondays (sections 1, 2 and 15 will do only procedure 1B) additional
data will be provided to each group. First, determine and record the temperature of the
room and of the de-ionized water from the tap.
Procedure 1A - measurement of precision
You will do the experiments in two ways. First, you will measure a fixed volume
(5, 10 or 20 cm3) using 3 different glassware to measure the volume to obtain
three different measurements of the density. In each set you will need at least 5
data points. For each data point (volume and mass) the measurement should be
done thrice.
a. You will first measure the volume using the graduated cylinder.
b. You will then repeat the measurement using a burette to determine the
volume.
c. In the final set of measurements, you will use a volumetric pipette to
determine the volume.
Make a table using the data obtained
Procedure 1B - determining density
In this second method, you will use the burette and analytical balance to measure
the mass of 5 different volumes of water (eg 5, 10, 15, 20 and 25 mL). Repeat
each set of measurement least once and the masses obtained should be in
agreement (within 0.005g)
Please also begin your lab book by putting in a title, page number as well as a brief
purpose section (why are you doing this lab? What are you trying to figure out? What
instruments/technique do you expect to be using to collect your data?) This portion of
the prelab will be required for all labs.
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Prepare tables in your notebook to and enter the data. You need to use the correct
number of significant figures, show all your calculations, and use the proper units for
each number. Prepare the graphs as discussed below, and when you are finished, paste a
copy in your notebook and have them graded before you leave the lab.
Preparing a graph
Take the data and make a plot of mass vs. volume. Be careful to choose the proper chart
type (XY Scatter). Once this is done, find the linear regression that best fits the graph.
What is the equation representing this line? How good of a fit does this represent? Be
sure to label the graph. You should not have a legend on the graph, since there is only
one line on each graph. Be sure to eliminate it.
Look to see if there are any data points that simply seem not to make any sense. Do you
feel that you could justify their removal? If so why? (Remember with your own data,
you can always eliminate data points if you feel there is a justifiable reason.) If you do,
re-graph the data without that point. Is there any notable improvement in the accuracy of
your trend-line?
Just to add one more useful skill to this, copy your three graphs (one for each type
of glassware used to measure volume - pipette, burette, graduated cylinder) and paste
them into a word document (and of course label them in Word.)
Once you have this done, print the graph (one copy for each member of the
group), paste it in your notebook and have it graded by your LA.
Report
Your report for this week should include the following sections: Title page, procedure,
and answers to the questions below. The primary focus this week will be on your
procedure.
Questions
1. When would it be appropriate to use a burette for measuring volume?
2. When would it be appropriate to use a pipette for measuring volume?
3. When would it be appropriate to use a graduated cylinder for measuring volume?
4. Which method was most appropriate for measuring the volume in this experiment?
Why? (Hint: Answer this question based on your data)
5. What is the density of the substance you measured? (Hint: Answer the question
fully, present your table and or graph here or refer to it if you have presented your
data before. Tell how you came to your conclusion. Did you just use the average
based on all your measurements? Did you decide that one method was more accurate
and use that value?)
6. What is the error in this measurement? How well do you know this value?
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7. Identify each of the following properties as an intensive property or extensive
property of matter:
a.
b.
c.
d.
e.
boiling point
freezing point
volume
mass
length
8. If you had an unknown substance and were asked to identify it, would you use the
intensive properties of the substance or the extensive properties of the substance?
Why?
*-standard data for the density of water is provided in the associated document
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