Determination of Density. Density is a measure of the concentration of matter in an object. It is a function of the distance between the molecules in a substance as well as the amount of mass possessed by the atoms comprising the respective molecules. Materials with the same composition that have more closely-packed atoms are denser than those which have greater distances between atoms. Similarly, materials which possess atoms that are situated at the same distance from each other but possess different masses have different densities. As we will see, temperature and pressure, conditions which directly effect a material's physical state, likewise effect the density of a material. All substances possess a characteristic density at a specific temperature and pressure.
Introduction
Triple Beam Balance
Meter Stick (or metric measuring tape)
100 ml graduated cylinder
Large wood block
Small wood block
Aluminum cylinder
Aluminum block
Sheet of aluminum foil
Tap water
Rectangular sponge
Methods Employed in the Determination of the Density of Solids and Liquids
Conditions Affecting the Density of Matter. Generally speaking, solids possess the highest density, followed by liquids, and then by gases which usually possess the lowest density, although there are some important exceptions. Since the states (or phases) of matter are directly related to conditions of temperature and pressure, it follows that both in turn have a direct influence upon a material's density. Generally speaking, decreases in temperature and increases in pressure increase a material's density, whereas increases in temperature and decreases in pressure act to decrease a material's density. Again, as previously stated, there are exceptions to this generalization which must be clarified. Water, for example, the most common substance at Earth's surface and comprising living tissue, attains its greatest density in the liquid phase at 3.98 degrees Celsius. The fact that styrofoam (a solid) always floats on water (a liquid) demands that styrofoam possess a lower density than that of liquid water. Size and shape have no effect on a material's density, provided that pressure and temperature remain unchanged.
Mathematical Determination and Units of Density. The calculation of a body's density may be simply obtained from the following equation, provided mass and volume are known
Density = Mass/Volume
where mass is expressed either in grams or kilograms, volume is then expressed in either cubic centimeters (or milliliters for liquids) or cubic meters, and density is expressed in either grams per cubic centimeter, grams per milliliter, or kilograms per cubic meter. (It is important to note that the latter is the chosen unit of density for physics since it adheres to the MKS (SI) system of measurement.)
Practical Importance of Density. Since all substances possess a characteristic (and therefore diagnostic) density, this means that a piece of silver, for example, always has a density of 10.5 grams per cubic centimeter when measured under standard laboratory conditions. If you were offered a piece of expensive silvery jewelry by a suspicious precious metals merchant who steadfastly claims it to be comprised of bonafide silver, for example, you could simply and quickly alleviate your anxiety over the authenticity of the piece by calculating the ratio of its mass to its volume. If the piece possessed a mass of 105 grams and occupied a volume of 10.0 cubic centimeters, the quotient of the resulting ratio would instantly dispel your suspicions and confirm its genuineness since a value of 10.5 grams per cubic centimeter would be obtained, the true density of silver.
Objectives
In this particular exercise you are going to
1. determine the mass of selected samples of matter of different size, shape, physical state,
and composition;
2. determine the volume of selected samples of matter of different size, shape, physical state,
and composition;
3. determine the density of selected samples of of matter of different size, shape, physical state,
and composition;
4. explore the mathematical relationships between mass, volume, and density;
5. explore the physical relationships between temperature, pressure, shape, size, composition,
and density;
6. demonstrate operational mastery of the lab apparatus; and
7. demonstrate the mathematical relationships between length, width, thickness, mass, and
density of a rectangular solid.
Materials
Procedure
1. First, determine the masses of the following materials with the triple beam balance:
Large wood block
Small wood block
Aluminum cylinder
Aluminum block
Sheet of aluminum foil
100 ml graduated cylinder
20 ml of tap water
Rectangular sponge
2. Then determine the volumes of the following materials with either the metric ruler or the
graduated cylinder:
Large wood block
Small wood block
Aluminum cylinder
Aluminum block
20 ml of tap water
Rectangular sponge
3. Then determine the density of each material listed below (in grams per cubic centimeter or
grams per milliliter):
Large wood block
Small wood block
Aluminum cylinder
Aluminum block
20 ml of tap water
Rectangular sponge
4. Following the steps and procedures outlined above, determine
the density of the sponge if it were squashed down to a thickness of 1.0 cm;
the density of the sponge with 20 ml of water added to it; and
the area of the sheet of aluminum foil (in square centimeters)
5. Enter all data and calculations on the lines provided below.
6. Answer all questions at the end of the laboratory in full sentences, showing all work and
calculations as required.
Useful Equations
Area of a Rectangle = Length x Width
Volume of a Rectangular Solid = Length x Width x Height
Volume of a Right Cylinder = 3.14 x Radius x Radius x Height
Density = Mass/Volume
Data and Calculations
Mass: (Procedure 1):
Large wood block
Small wood block
Aluminum cylinder
Aluminum block
Sheet of aluminum foil
100 ml graduated cylinder
20 ml of tap water
Rectangular sponge
Volume: (Procedure 2):
Large wood block
Small wood block
Aluminum cylinder
Aluminum block
20 ml of tap water
Rectangular sponge
Density: (Procedure 3):
Large wood block
Small wood block
Aluminum cylinder
Aluminum Block
20 ml of tap water
Rectangular sponge
Miscellaneous: (Procedure 4):
Density of sponge squashed to 1.0 centimeter thick
_______________ grams per cubic centimeter
Density of sponge with 20 ml of tap water added
_______________ grams per cubic centimeter
Area of the Aluminum Foil Sheet
_______________ square centimeters
Questions
1. Summarize the general relationship between the density of solids and the density of liquids as revealed by
this experiment.
2. List potential sources of error in this experiment.
3. How does this experiment illustrate the relationship between mass and volume in the density equation?
4. What should a graph of mass versus volume resemble if we were to plot the respective mass and volume
values for each body as points in a Cartesian coordinate field and connect each point with a straight
line to the origin? To what is the slope of the plotted line equivalent? (Think!)
5. Based on the data obtained in this experiment, compare, contrast, and explain the observed differences, if
any, between the density of the sponge obtained in procedure 3 and the densities of the sponge
obtained in procedure 4.
6. Based on the data obtained in this experiment, calculate the thickness of the sheet of aluminum foil.
(Think! You have all the data you need to calculate this.) Show all work and remember to include
units in each step.
7. Based on the data obtained in this experiment as well as your knowledge of the metric system, express the
density of tap water in kilograms per cubic meter. Show all work and remember to include units in
Triple Beam Balance
