# Intoduction

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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.
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?

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?

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
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
Experimental Determination of Density for Rectangular Shaped Objects - Student Lab Report

Student Name:

Experiment #1:

Experimental Density:                                                 2.7

density was not correct on the
first try. What did you do
differently to obtain the correct
results?

Experiment #2:

Experimental Density:                                                0.79

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
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

```
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