# Density is a physical substance of all matter

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```					                                  Density Determination
INTRODUCTION
Density is a physical property of all matter. This intensive characteristic can be used to help identify
a substance. Density is defined as the amount of matter in a given unit of volume. The formula for
density is mass/volume (D=m/v). The mass is measured in grams and is found by placing the object
on the balance. The volume can either be determined by direct measurement, indirect measurement,
or .using calculations. If a solid is placed in water, the solid will displace a volume of water equal to
its own volume. So, the difference in volume of the water will be equal to the volume of the object.
Calculation would be best for a regularly shaped solid, like a cylinder Volume by displacement is
best for irregularly shaped objects where a formula is not practical. Remember that 1 cm3 = 1mL.

PRE-LAB ASSIGMENTS:
1. Read the Wikipedia article on density (http://en.wikipedia.org/wiki/Density).
a. Why is density an intensive physical property while it is derived from two extensive
physical properties (mass and volume)?
b. How could Archimedes tell whether the kind’s goldsmith was embezzling gold?

PURPOSES:
    Determine the density of solids with a regular shape, an irregular shape, and a liquid.
    Learn how to determine “wet” volume (using displacement)
    Use density to identify an irregular solid (unknown)
    Determine the density of water experimentally and calculate percent error.

MATERIALS:
Electronic balance                                       1 specula
10 mL and 25 mL graduated cylinders                      1-50 mL beaker
Metric ruler                                             Unknown liquid
1 cylinder                                               Water
2 disposable pipets

PROCEDURE:
I: Density of regular geometric object:

1.   Briefly make a qualitative observation of the density cylinder.
2.   Mass the density cylinder and record the mass in Table 1.
3.   Measure the length and diameter of the density cylinder and record the measurements.
4.   Calculate the volume of the density cylinder by using the formula of a cylinder. Use sig. figs.
and proper labels. Record this information in Table 1.

II. Density of an Unknown Liquid

5. Weigh the empty 10 mL graduated cylinder.
6. Place 9 mL. of unknown liquid into a 10 mL. graduated cylinder and dry the outside of the
cylinder. Record the exact volume by reading the graduated cylinder carefully. Record the mass,
remembering to subtract the mass of the graduated cylinder. (Of course, if you read this step
ahead of time, you massed the empty graduate before you added the water). Record this data in
Table 2.
7. Determine the identity of the unknown liquid by consulting the provided list of possibilities.

III. Density of an Irregularly Shaped Solid:

8. Put the irregular solid in a weigh boat (tared), and determine its mass. Record this in Table 3.
9. Determine the volume of this mass of the irregular solid by displacement in a 10 mL graduated
the water, then placing the solid into the cylinder, reading the new volume and the difference is
the volume of the irregular solid).
10. Determine the density of the irregular solid. Use correct labels and sig. figs. Record in Table 3.
11. Determine the identity of the unknown irregularly shaped solid by consulting the provided list of
possibilities.

DATA:

Table 1 ______________________________________________________

Cylinder   Mass Length Diameter Radius Volume     Density                              Density       Percent
Description (g)    or     (cm)    (cm)   (cm 3)  Experimental                           Accepted       Error
Height                 ( r2 h)   (g/mL)                                (g/mL)        (%)
(cm)

Table 2 ______________________________________________________________

Substance        Mass of       Mass of       Mass of     Volume       Density                Density       % Error
graduated       empty       Liquid (g)    (mL)      Experimental            Theoretical
and liquid   cylinder (g)
(g)
Unknown
Liquid
Water

Table 3 _______________________________________________________________

Irregular         Mass (g)     Volume        Density       Density                %          Identification of
Solid                         (mL)       Experimental   Theoretical            Error          Substance
(g/mL)            (g/mL)
A
QUESTIONS: (complete sentences)
1. A metal cylinder with 26.0 mm diameter and 75.0 mm height has a density of 8.60 g/mL. Calculate
its mass.
2. A metal sphere weighing 18.48 g is added to 20.00 mL of water in a graduated cylinder. If the density
of the metal is 4.50 g/mL, what will be new level of water in the graduated cylinder?
3. In this experiment, could you have used volume displacement method with water for finding the
volume of a wood cube, assuming the cube can fit into the cylinder? Explain why or why        not.
4. How will you find the volume of an irregularly shaped object that would dissolve in water?
5. Explain why the density of a solid remains constant with varying temperatures, but densities of
liquids and gases change with changing temperatures.
6. The density of steel is 7.8 g/mL, a value much larger than that of water (1.0 g/mL). Hence steel
nuggets sink to the bottom when dropped in water. Then why do modern ocean liners built with
steels float and are capable of carrying large amount of cargo or passengers?

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