CHEMISTRY LAB
MASS, VOLUME, AND DENSITY

INTRODUCTION:

Mass is a measurement of the amount of matter in a sample, while volume is a measurement of the space occupied by a sample of matter. In this experiment, you will measure the mass and volume of metal samples. You will then use the data obtained, to determine whither there is any constant relationship between the mass and the volume of a given substance.
Measurements of mass are made on the balance, and measurements of volume in a graduated cylinder.
Measurement of volume in a graduated cylinder is always made by reading the mark at the bottom of the meniscus. The reading is made with the eye positioned at the level of the liquid surface.
The volume of a solid may be calculated from its dimensions, if the solid is regular and free of air space. If, on the other hand, the solid is irregular or contains air space (as sand does, for instance), its volume must be determined in another way, such as by water displacement. Displacement measurements are made as follows. A graduated cylinder large enough to accommodate the sample of solid is partially filled with water. The volume of the water is noted. The solid is then submerged in the water, and the volume is read again. The difference between the final volume and the initial volume represents the volume of the solid. The solid must be completely submerged in the water for this method to yield accurate results, and all the air bubbles adhering to the submerged solid must be dislodged. This method is obviously only useful for solids that are insoluble in water.
As you conduct this experiment, try to keep in mind the distinction between measurements of mass and volume and other types of measurement, such as those of temperature, which are independent of the amount of material involved.

MATERIALS:

Balance
Weighing dishes (5 per metal tested)
Ruler
Samples of metal shot

Aluminum (at least 80 grams)
Zinc (at least 160 grams)
Copper (at least 250 grams)
Lead (at least 310 grams)

PROCEDURE:

1. Using the balance, obtain the following 5 samples of aluminum shot, in separate weighing dishes: 5.0 g, 10.0 g, 15.0 g, 20.0 g, and 25.0 g. Record the masses on the DATA TABLE for aluminum.

2. Find the volume of your metal samples in the following way. Fill a 25-mL graduated cylinder with no more than 10 mL of water. The volume only needs to be enough to completely cover the sample when added, but must not go over the 25 mL mark with the sample added. Record the initial volume of the water on the DATA TABLE in the appropriate place. Tilt the cylinder and slide your metal sample carefully into the water, so that it does not break the cylinder and so that water does not splash out. If the metal sample is not completely submerged, you must remove the sample and start again, using a larger initial volume of water. It is important that the metal sample be dry before it is immersed in the water. Otherwise, error will be introduced into the volume measurement. Record the final volume of the water containing the submerged metal sample in the DATA TABLE. Repeat for all 5 samples.

3. Calculate the volume of each metal sample by subtracting the initial volume of water in the cylinder from the final volume. Put the answers in the appropriate place on the DATA TABLE.

4. Plot a graph relating mass and volume. Plot mass on the vertical or y axis, and volume on the horizontal or x axis.

Decide whither the point (0,0) should be included in the graph. (When the volume of a sample is zero, will its mass also be zero?) The answer is of course, yes it will be, so the line will go through point (0,0).
Use a ruler to draw the best straight line of fit through the plotted points. Note that not all of the points will lie on the best line of fit. However, approximately as many points should lie above the line, as lie below the line, and be about the same distance from the line. There may or may no be any points on the line. This is somewhat like an average, and corrects for experimental error. The correct answers are now on the line, not the raw data points.

8. Determine the slope of the line. Remember that if a line goes through the point (0,0) its slope is y/x . In the graph that you have plotted, y/x is equal to mass/volume, which is the formula for density. Thus, the slope of the line you have drawn represents the density of the metal you have examined. Record the density in the proper place on the DATA TABLE. Your volume unit is milliliters, but 1 mL = 1 cm3 , so your density value can also be given as grams per cubic centimeter.

9. Now repeat the procedure for the other metals. The masses to use are as follows:

Zinc = 10.0 g, 20.0 g, 30.0 g, 40.0 g, and 50.0 g.

Copper = 16.0 g, 32.0 g, 48.0 g, 64.0 g, and 80.0 g.

Lead = 20.0 g, 40.0 g, 60.0 g, 80.0 g, and 100.0 g.

10. Look up the density for the metals used on a periodic table or in a textbook. Compare the densities you obtained, with the accepted values.

Mass (g) DATA TABLE: for Aluminum Density of Aluminum = ______ g/mL

Mass (g) DATA TABLE: for Zinc Density of Zinc = ______ g/mL

Mass (g) DATA TABLE: for Copper Density of Copper = ______ g/mL

Mass (g) DATA TABLE: for Lead Density of Lead = ______ g/mL

PREPARED GRAPH PAPER: