Estimation of Atomic Mass from Specific Heat
Before the development of mass spectrometry, it was difficult to determine the atomic mass of an element. In 1819, Dulong and Petit discovered that the product (about 26.4) of the atomic mass and the specific heat was nearly the same for many solid elements. This approximation has been found to be valid for metals and solid elements with atomic masses over 40.
Specific heat can be thought of as the amount of heat required to raise the temperature of one gram of a substance one degree Celsius. Specific heat constants have the units of J/g (C. The values of these constants vary greatly. The constant for water is 4.184 J/g (C, while the value for copper is 0.385 J/g (C. This means that over ten times as much heat would be required to raise the temperature of a water sample as compared to an equal mass of copper.
In this experiment you will carry out a standard procedure to determine the specific heat for a metal. Then using the Law of Dulong and Petit, the atomic mass of the metal will be determined. Atomic Mass = 26.4/ specific heat.
samples of metals large test tube
400 mL beaker hot plate
balance foam coffee cups
• An apron and goggles must be worn in the laboratory.
• Avoid contact with the hot plate.
1. Place about 200 mL of tap water in a 400 mL beaker and place it on the hot plate. Heat the water until it boils.
2. Select a metal cylinder to use for this experiment and mass it. Record the mass in the data table.
3. Carefully transfer the metal to a large test tube. Place the test tube in the hot water bath, and let it sit for 10 minutes.
4. While the metal is heating in the hot water bath, obtain a styrofoam cup. Tare it on the balance. Place about 100 mL of distilled water in the cup, and place it on the balance again to determine the mass of the water.
5. While the metal...