 Lab: Density

Density is the measure of the amount of material (mass) in a given space (volume) which is expressed as a ratio (Mass/Volume).  The density of a given substance is based on the arrangement of the atoms within element or compound.  The closer the atoms are packed the greater the density.  Within the study of Earth Science, the differences in the density of substances create convection currents which are responsible for the formation of weather and the movement of the tectonic plates.

Within scientific measurement it is important to know how to use different measuring equipment and to express the accuracy of your measurements.  Percent error is the amount by which any measurement differs from a known or accepted value.  It is determined by the following equation:

percent error = (calculated measurement - accepted measurement)/accepted measurement x 100%

In this lab you will measure the density of a cylinder using cm sticks (r), calipers (c), and a graduated cylinder (g).  You will also measure the density of an irregular object via the same method.  After you have completed the three measurements you will obtain the accepted value for the density from your instructor and find the percent error for each type of measurement.

Procedure:

1)    Use a triple beam balance to find the mass of the cylinder.  Record the mass of each cylinder in your data chart.

2)    Measure the volume of your cylinders using the cm stick, calipers, and the graduated cylinder (using a spill cup). Record the volume of each cylinder in your data chart.

Formula:    (pr2 x l)

3)    Calculate the density of your samples and record in your data table.

Formula:    Mass/Volume

4)    Obtain the accepted measurement from your instructor and calculate the percent error for each type of measurement.

5)    Repeat the procedure for the irregular item and compare it to the accepted value for steel.

Data Table:

 Object Mass (g) Length (cm) Width (cm) Radius (cm) Volume (cm3) Density (g/cm3) % error Copper (r) (c) (g) xxxxxxx xxxxxxx xxxxxxx Steel       (r) (c) (g) xxxxxxx xxxxxxx xxxxxxx Brass      (r) (c) (g) xxxxxxx xxxxxxx xxxxxxx Aluminum (c) (g) xxxxxxx xxxxxxx xxxxxxx Bolt        (r) (c) (g) xxxxxxx xxxxxxx xxxxxxx

Questions:

1)    What accounts for the difference in densities of the different metals?

2)    If the pieces of metal were cut into smaller pieces would there be a change in the density?

3)    Which of the measuring methods produced the most accurate results?  Explain.

4)    Graph the accepted value of the metals against your different measuring techniques. (line graph with a line extending from the 0 through the data point of the accepted measurement.) 5)    What were some potential sources of error for you measurements?