The purpose of this lab is to determine the identity of an unknown metal, and to prove whether the laws of thermodynamics hold when determining this identity. Using the accepted specific heat of water (4186 J/kg · oC), heat flow between two different sets of water though the conduction of an unknown metal can provide useful data in determining the identity. The heat transfers can be calculated to approximate the specific heat of the unknown metal.
When heat is transferred to an object, the temperature of the object increases.
When heat is removed from an object, the temperature of the object decreases. The relationship between the heat (q) that is transferred and the change in temperature (DT) is: q = mCDT = mC · (Tf – Ti).
After the specific heat of the metal is found, it can then be compared to known specific heat values of various metals, which in turn will allow for a probable identity of the unknown metal to arise.
The identity of the unknown metal is aluminum.
This can be inferred from the unknown metal’s appearance, which resembles aluminum it its color, light weight, and luster. The laws of thermodynamics will hold when determining the unknown metal. The laws of thermodynamics must apply in order for heat flow to occur during the experimentation.
The materials used in the lab were two calorimeters (insulated, Styrofoam containers), an unknown metal in the shape of a wide horseshoe, two thermometers, a balance, water, a beaker, and a Bunsen burner.
1.Measure the weight of the Pyrex beaker, and then pour 200 mL into the beaker. Weigh the beaker filled with water. Record both weights to find the weight of the water by itself. Let this mass of water be labeled ‘1’. Next, pour the water into one of the calorimeters and take the temperature of it. This temperature should be the room temperature and the same as the unknown metal’s temperature.
2.Pour 200 mL of water into the beaker and weigh the beaker filled with water. Record the weight. Let this mass of water be labeled ‘2’.
3.Use the Bunsen burner to heat up the 200 mL of water in the beaker to 75o C. Then pour the hot water into the other calorimeter.
4.Set-up the calorimeters by placing the thermometers and the unknown metal in their specific places.
5.Record temperatures of both calorimeters every minute until thermal equilibrium is reached.
6.Clean and return all materials and dispose of any waste.
The graph indicates that heat flow did undergo during the experimentation. The cold water increased in temperature, while the hot water decreased. The two liquids underwent changes in temperature until they both reached thermal equilibrium. This thermodynamics law is called the Zeroth Law of Thermodynamics. This law basically states that two bodies will naturally reach thermal equilibrium when in contact. The First Law of Thermodynamics was obeyed as well. Only heat from the warmer body went to the colder body. Heat only travels in one direction, from the hot to the cold, as can be seen from the graph.
My hypothesis of the unknown metal being aluminum was correct. The results of my lab showed that the unknown metal was aluminum, and later it was said that the metal had in fact been aluminum. The lab calculations went well. The values were somewhat disparate however. For example, the specific heat was found to be 1200 ± 110 J/kg · oC, but the actual specific heat of aluminum is 900 J/kg · oC. This difference can be attributed to the imperfect insulation of the calorimeters. Some heat must have been lost during the experiment, which may have caused a distortion in values as a result. Also, the metal was exposed to the outside air, and likely lost some heat to the air. Overall, the lab was a success. The only improvements I would suggest are to have better insulators and more precise instruments. Better insulation would yield improved results. The metal, which was transferring the heat, should have been insulated so that heat could not escape during the heat transfer. More precise instruments would cut down on the uncertainties, which then would allow for better and more accurate results.