Laboratory - Density
Purpose: To determine the density of various forms of metallic elements. The methods involved are by determining the Mass (g) and Volume (mL) using a metric balance and a graduated cylinder (water displacement). Those elements recommended for this activity are Aluminum (Al), Cadmium (Cd), and Zinc (Zn). The identity of these elements can be made optional.
Procedure: It is advised that the process of determining mass be conducted first to prevent the possible error of weighing water that might adhere to the sample. Because it is necessary to express the density of solids and liquids in grams per milliliter utilization of a scale capable of measuring in grams is advisable. It is certainly possible to utilize other means of measuring weight but those will most likely require a conversion process. The choice of graduated cylinders should be based upon the size of the sample for which the volume is to be determined. It is desirable to select the smallest possible graduated cylinder that will hold enough water to cover the sample. Reading the volume should be done by noting the meniscus (the bottom curvature of the liquid).
Results: Here the student should provide all necessary formulas, Density=Mass/Volume, and other data including any graphs or charts. In this particular lab. it would be advisable to indicate the volume of water in the cylinder both before and after the addition of the unknown metal sample. Showing clearly how the resulting volume of the sample was determined. Likewise, if the sample, for weighing, was placed in a container then both the container empty and with the sample should be provided.
Conclusion: This is the time for the student to summarize his/her observations and calculations. This is the time to include comments which might provide insight which otherwise might not have been evident. With the accurate determination of this information it is highly likely the identity of the element can be determined (by using a table of densities chart).