Density of Glass

Introduction

Does the shape, size, or amount of a substance change its density? You will measure the density of bent and straight pieces of glass to see if the shape or size affects the density. To measure density you will need to determine the weight and volume of each piece.

Go to Top

1. Obtain 6 pieces of glass tubing, 3 straight and 3 bent. (Each of the 6 pieces must fit into a 50-mL graduated cylinder and when inserted, should not extend above the 35 mL calibration line.)
2. Keep track of the weight and volume data for each piece of glass by completing the data table provided. This data will be used to make a graph.
3. Place about 35 mL of water in the 50-mL graduated cylinder. Record the meniscus under the heading in your data table labeled "initial volume." Place the cylinder on the pan of a balance. Record the mass of the cylinder and its contents under the heading in your data table labeled "initial mass." Also record this point on a piece of graph paper with volume as the x-axis and mass as the y-axis.
4. Place one piece of glass in the cylinder. Record the new meniscus under the volume column. Weigh and record the new mass under the mass column. Plot the point on the graph.
   

   

5. Repeat this sequence until all of the pieces have been added to the cylinder.
   

Go to Top

1. Plot a graph using all the masses (y-axis) and volumes (x-axis) from the data table. Draw a line that goes through the average of all the points. From the slope of the line calculate the density of glass.
   Slope (density) =Δy/Δx
2. The density of iron is 7.86 g/mL. A student's experimental value was 6.66 g/mL. Suggest an error or combinations of errors the student may have made and explain your choice:
   1. High mass and/or low volume.
   2. Low mass and/or high volume.
3. Describe another method to determine the volume of the glass.

Go to Top

Safety

Wear eye protection at all times in the laboratory.

Go to Top

1. Size, shape, or amount of a substance does not change the density of the substance. The students should discover that the slope of the line and the calculated density from the formula are almost the same. Also that the density of l, 2, or 6 pieces of glass is the same.
   Note: Glass tubing should not be sealed at either end for accurate results.
2. Some combination of low mass and high volume will lead to a lower than expected density. Spilling some water leads to a lower mass, for example.
3. If the objects have uniform shapes dimensions, the dimensions can be measured and the volume calculated. Suppose the glass objects were prepared from uniform pieces of glass rod. The volume of a cylinder is 4πr²l, for example, where π is the constant 3.141, r is the radius of the cylinder, and l is the length of the cylinder.
   

Go to Top

Go to Top

You may use other substances and, because of the way in which the experimental procedure is designed, different forms of the substance may be used. For example, copper rod, shot, heavy foil, heavy wire, tubing, pipe, screws, nuts, and bolts can be used.

Fire polish (heat in a hot flame to soften) the sharp ends of the glass before giving them to students.

Go to Top

• 1 Balance
• 50-mL graduated cylinder
• 6 pieces of glass tubing: 3 linear and 3 differently shaped pieces. (All pieces should fit loosely into the graduated cylinder and none should extend above the 35 mL calibration line. A mixture of 6, 7, and 8 mm by 6 cm tubing is suggested. It is a good idea to make these pieces during a previous lab glass bending. Solid glass and colored glass are good unknowns.)

Go to Top

The Woodrow Wilson microscale version of this lesson was developed by:

Catherine B. Ireland
Division Avenue High School
Division Avenue
Levittown, New York ll756

Go to Top