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Introduction into Density
Density = mass/volume
Mass is measured using a balance with a certain precision or decimal places.
Volume can be measured using a variety of methods. We will use a ruler to measure the length, height, and
width of regular shaped cubes. The volume of a cube = l x w x h. The ruler that you will be using has a
precision of 1 millimeter meaning that all measurements should be rounded to the nearest millimeter. Make
sure you are aware that volume and density commonly are reported in cm3. To convert millimeters to
centimeters, use the following conversion: (10mm = 1cm).
Example Problem:
A student measured the mass of a metallic cube and obtained a result of 48 grams. Using a ruler, the student
collected the following dimensions of the cube: l = 15 millimeters, w = 19 millimeters, h = 21 millimeters.
Calculate the experimental density of this metallic cube and determine the identity of the unknown metal
using a list of known metal densities.
Example Answer:
Mass (g) Length (mm) Width (mm) Height (mm) Volume = l x w x h = mm3
48 15 19 21 5985
density = 48/(15x19x21) = 0.0080 g/mm3 = 8.0 g/cm3
The experimental density matches closest to Brass (density = 8.03g/cm3)
Therefore, the student determined that the unknown metallic block is brass.
Determination of Density of Three Different Regular Shaped Objects
Experiment #1: Measure the metallic object on your desk and enter the experimental data using the tabs below.
Measurements with a Ruler and a Balance (Measure to the nearest millimeter)
3 3
Mass (grams) Length (mm) Height (mm) Width (mm) Volume (mm ) Density (g/mm )
55.6 25 20 41 20500 0.0027
55
6
Question: Lets assume your density was not correct on the
first try. What did you do differently to obtain the correct
results?
Student Answer:
Experiment #2: Measure the wooden object on your desk and enter the experimental data using the tabs below.
Measurements with a Ruler and a Balance (Measure to the nearest millimeter)
Mass (grams) Length (mm) Height (mm) Width (mm) Volume (mm3) Density (g/mm3)
12.8 26 25 25 16250 0.00079
11
18 Question: Procedurally, what could be done to improve the
precision and accuracy of this lab? How could the lab be
improved in terms of instrumentation?
Student Answers:
Experiment #3: Measure the man-made object on your desk and enter the experimental data using the tabs below.
Measurements with a Ruler and a Balance (Measure to the nearest millimeter)
Mass (grams) Length (mm) Height (mm) Width (mm) Volume (mm3) Density (g/mm3)
40.6 35 24 17 14280 0.0028
39
16 Question: Use the attached tab of known densities to
determine the type of man-made material in your lab.
Student Answer:
r Shaped Objects
ntal data using the tabs below.
3
Density (g/cm )
2.7
Correct! The cube is Aluminum
your density was not correct on the
do differently to obtain the correct
ata using the tabs below.
Density (g/cm3)
0.79
Correct! The cube is Red Oak
y, what could be done to improve the
of this lab? How could the lab be
nstrumentation?
al data using the tabs below.
Density (g/cm3)
2.8
ched tab of known densities to
man-made material in your lab.
Experimental Determination of Density for Rectangular Shaped Objects - Student Lab Report
Student Name:
Experiment #1:
Experimental Density: 2.7
Question: Lets assume your Student Answer:
density was not correct on the
first try. What did you do
differently to obtain the correct
results?
Experiment #2:
Experimental Density: 0.79
Question: Procedurally, what Student Answers:
could be done to improve the
precision and accuracy of this
lab? How could the lab be
improved in terms of
instrumentation?
Experiment #3:
Experimental Density: 2.8
Question: Use the attached tab Student Answer:
of known densities to determine
the type of man-made material
in your lab.
Experimental Accuracy and Precision
Density Each measurement contains a degree of
There is no such thing as a perfect measurement. Review
uncertainty due to the limits of instruments and the people using them. In laboratory exercises,
students are expected to follow the same procedure that scientists follow when they make
Introduction
measurements. Each measurement should be reported with some digits that are certain plus one
Density, one of the physical properties of matter, describes the mass of a substance per unit volume.
digit with a value that has been estimated.
All matter has density. The volume of solids and liquids is typically measured differently, therefore
For example, if a student is reading the level of water in a graduated cylinder that has lines to
density is usually measured as gramshe or she should report the volume ofper milliliter (g/mL), or
mark each milliliter of water, then per cubic centimeter (g/cm3) or grams the water to the tenth
some variation ml.) This units. show that the 18 mls are certain and the student estimated the
place (i.e. 18.5 of these SI wouldTemperature and pressure can affect the density of some
substances, so in order water level was about half way between the 18 and 19 measure their
final digit because the to compare the densities of different substances, you mustmark.
mass and volume at the same temperature and pressure.
Two concepts that have to do with measurements are accuracy and precision.
Density of close
The accuracy of the measurement refers to howSolids the measured value is to the true or
accepted value. For example, if you used a balance to find the mass of a known standard 100.00
The mass of you got a be measured using a balance. The volume (amount be very accurate. One
g mass, and a solid can reading of 78.55 g, your measurement would notof space an object takes
up) of a solid can be measured accuracy and a graduated that accuracy can be determined by only
important distinction betweenusing a ruler or precision is cylinder. If the object is regularly-shaped,
such as a cube or rectangular prism, can only be determined with multiple measurements.
one measurement, while precision the volume can be found by measuring the dimensions with a
ruler and using the following equation: volume=length*width*height. The volume of a cylinder can be
Precision refers to radius of the circular group of measurements actually are using the
found by measuring thehow close together aend and the height of the cylinder, and to each other.
following has nothing to do with the true or accepted value of a for finding the so it is of other
Precision equation: volume=Π*radius2*height. There are equationsmeasurement, volume quite
regularly-shaped objects, but a graduated cylinder can also be cases, when precision is the water
possible to be very precise and totally inaccurate. In many used. The displacement of high and
the fault can graduated instrument. If to that objects thermometer is not
accuracy is low, is placed in thelie with thecylinder is equal a balance or a volume. Note that 1mL=1
when the object
working correctly, they might consistently give inaccurate answers, resulting in high precision
cm3, so volume (and therefore density) comparisons can be made, regardless of the method used to
and low accuracy.
calculate the volume. The density of the objects can then be found by using the following equation:
density=mass/volume.
A dartboard analogy is often used to help students understand the difference between
accuracy and precision. Imagine a person throwing darts, trying to hit the bull's-eye. The closer
the dart hits to the bull's-eye, the more accurate his or her tosses are. If the person misses the
dartboard with every throw, but all of their shots land close together, they can still be very
precise.
You must strive for both accuracy and precision in all of your laboratory activities this year.
Make sure that you understand the workings of each instrument, take each measurement
carefully, and recheck to make sure that you have precision. Without accurate and precise
measurement your calculations, even if done correctly, are quite useless.
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Densities sorted by Material Category
Category Material Density (g/cm3)
-------- --------------- --------------
Liquid Acetone 0.792 Other Cork 0.24
Liquid Benzene 0.737 Other Glass 2.6
Liquid Ethyl Alcohol 0.802 Other Graphite 2.163
Liquid Gasoline 0.721 Other HDPE plastic 0.955
Liquid Glycerin 1.260 Other Lead Glass 2.8
Liquid Methyl Alcohol 0.809 Other Leather, common 0.945
Liquid Mineral Oil 0.914 Other Nylon 1.13
Liquid Seawater 1.025 Other Paper 0.929
Liquid Vegetable Oil 0.93 Other Paraffin 0.898
Liquid Water, 100 °C 0.9581
Other PVC 1.405
Other Quartz 2.650
Liquid Water, 4 °C 0.99997
Other Quartz Glass 2.2
Liquid Water, Ice 0.897
Other Rubber 1.506
Metal Aluminum 2.702
Metal Brass 8.03 Wood Balsa 0.125
Metal Carbon Steel 7.84 Wood Birch 0.705
Metal Copper, Pure 8.92 Wood Cherry 0.433
Metal Gold, Pure 18.88 Wood Mahogany 0.705
Metal Iron 7.86 Wood Poplar 0.420
Metal Lead 11.343 Wood Red Oak 0.750
Metal Mercury 13.594
Wood Southern Pine 0.500
Wood Sugar Maple 0.689
Metal Nickel 8.90
Wood Walnut 0.593
Metal Platinum 21.45
Metal Silver, Pure 10.5
Metal Stainless Steel 8.03
Metal Steel 7.615
Metal Tin 7.28
Metal Titanium 4.5
Metal Tungsten 19.35
Metal Uranium 19.05
Metal Zinc 7.14
Mineral Coal, Bituminous 1.346
Other Acrylic 1.17
Other Borosilicate Glass 2.3
Other Ceramic tile 2.502
