Density_Lab

Fall Semester Earth Science

John Dewey High School

Mr. Klimetz

Determining the Density of Matter

Laboratory No. 1

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

Wood block

Aluminum block

Brass/Copper block

Steel 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:

Wood block

Aluminum block

Brass/Copper block

Steel 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:

Wood block

Aluminum block

Brass/Copper block

Steel block

Tap water

Rectangular sponge

3. Then determine the density of each material listed below (in grams per cubic centimeter or

grams per milliliter):

Wood block

Aluminum block

Brass/Copper Block

Steel Block

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;

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):

Wood block

Aluminum block

Brass/Copper block

Steel block

Sheet of aluminum foil

100 ml graduated cylinder

20 ml of tap water

Rectangular sponge

Volume: (Procedure 2):

Wood block

Aluminum block

Brass/Copper block

Steel block

20 ml of tap water

Rectangular sponge

Density: (Procedure 3):

Wood block

Aluminum block

Brass/Copper block

Steel block

20 ml of tap water

Rectangular sponge

Miscellaneous: (Procedure 4):

Density of sponge squashed to 1.0 centimeter thick

_______________ grams per cubic centimeter

Area of the Aluminum Foil Sheet

_______________ square centimeters

Questions

1. How does this experiment illustrate the relationship between mass and volume in the density equation?

2. 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, in which mass is plotted on the y-axis and

volume is plotted along the x-axis, and connect each point with a straight line to the origin?

To what is the slope of the plotted line equivalent? (Think!)

3. How can we tell, without making measurements of volume or mass, that the densities of the aluminum

block, the copper/brass block, and the steel block are different?

4. 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.

__________ grams

__________ cubic centimeters

__________ milliliters

__________ cubic centimeters

__________ grams/cubic centimeter

__________ grams/milliliter

__________ grams/cubic centimeter