And there shall be a tabernacle for a shade in the daytime from the heat, and for a security and covert from the whirlwind, and from rain. Is 4:6 Thermal physics defines heat as the transfer of energy between objects due to a difference in temperature between them. Heat moves from the object at higher temperature to the object at the lower temperature. How much heat is needed to raise the temperature of an object exactly 1 o C depends upon two things: 1) the mass of the object, and 2) the chemical composition of the object. Since the energy needed to raise the temperature of an object 1 o C is dependent upon the mass, physicists have defined a term called specific heat capacity or specific heat. The Specific Heat of a substance is the amount of heat required to raise the temperature of 1-g of the substance by 1 o C. Water has a high specific heat at 4.18 J/g C. Metals usually have low specific heats. In other words, the same amount of energy (heat), raises the temperature of water more than it raises the temperature of metals. Specific heat is useful in the characterizing the identity of an unknown object. In this lab, you are going to determine (or verify) the identity of a metal by obtaining the value of the object s specific heat. Learning Objectives: Use a calorimeter to test the specific heat of an unknown metal and to identify it Materials Required: From Physics Kit Graduated Cylinders Student Supplied Stove, pot, oven mitts and tongs 8-oz Styrofoam cups, (2 for experiment + 1 for a lid) (or, you could use a straight Styrofoam lid) Metal object (see note*) *Requirements for metal object: Examples: hex bolt, screw, washers tied together, etc. Mass should be around 25 grams can combine several to achieve the mass It is helpful but not necessary to know the chemical composition of the object Safety Use caution with hot surfaces and boiling water. These can cause severe burns. Continually monitor each apparatus and all hot surfaces Experiment: The specific heat is unique for each substance. For example, the specific heat of water is 4.186 x 10 3 J/kg o C whereas that of lead is 1.29 x 10 2 J/kg o C. In this experiment you will heat a metal object to 100 o C by boiling it in water. You will transfer the object to water at room temperature (RT) and measure the change in temperature of 2015 Catholic Initiatives in Math and Science, LLC All Rights Reserved 1
the water. Since the specific heat of water, the mass, and change in temperature are known, the HEAT in Joules gained by the water can be readily calculated. Think about this: The amount of heat GAINED by the water must the same as the heat LOST by the object. The numerical value of the Q is known, but the sign is opposite. Now, since you know the heat, mass and ΔT for the object, you can calculate the specific heat for the object. A summary of the protocol design is shown below. Note: Good results in this experiment are very dependent upon highly accurate temperature measurements. Be precise and accurate in measuring. Procedure 1. Heat plenty of water in a pan until it is boiling vigorously 2. Prepare metal object: Use the scale to find the mass of the metal object(s) and record in Table 1 Optional: tie about 20 cm of string around the metal object(s) String will be used to transfer between locations without burning You may also use tongs to transfer from heat to the calorimeter 2015 Catholic Initiatives in Math and Science, LLC All Rights Reserved 2
3. Heat the metal object(s): When the water is boiling, place the metal objects in it Leave it for at least 15 minutes In the meantime, you can prepare the calorimeter (Step 4) Measure the temperature of the boiling water and record in Table 1 Note: this will be the initial temperature of the metal object (Ti screw) 4. Prepare the calorimeter Styrofoam cups will be used as a calorimeter since Styrofoam is a good insulator Take two Styrofoam cups and nest them one inside the other Weigh the Styrofoam cups and record the mass (Wi) You will use a third cup (or a lid) to keep heat in, but this will NOT be part of the mass calculations Poke a hole in the third cup or lid so that the thermometer will fit through Measure and pour 150 ml room temperature water into the cups (calorimeter) Note: you must do this with two allocations Weigh the Styrofoam cups (without the lid) with the water (Wf) By subtraction, calculate the mass of the water and record (kg) in Table 1 Wf Wi Water mass (g) Convert to kilograms 5. Record temperature of the water in the calorimeter Place the lid on the calorimeter and fit the thermometer through the lid, into the water Place thermometer in the center of cup without touching sides Allow the water to reach room temperature equilibrium, if it has not already Record temperature in Table 1 Note: this will be the initial temperature (Ti water) of the water 6. Transfer When the object has boiled for 15 minutes and water in calorimeter is steady, you will transfer the object from pot to the calorimeter Using tongs or the string, quickly transfer the hot metal object(s) to the calorimeter Do not allow the screw to touch the sides of the calorimeter Close the lid quickly 7. Monitor the temperature carefully Stir the water carefully with thermometer Read the temperature often without lifting the thermometer out of the water Continue this process until two consecutive readings are the same Record this temperature in Table 1 Note: this is the temperature at which the screw and water have reached thermal equilibrium This temperature is (Tf screw) and (Tf water) 2015 Catholic Initiatives in Math and Science, LLC All Rights Reserved 3
8. Determine the change of temperature for the screw and record in Table 1 Sign is important! ΔT = T initial T final 9. Determine the change of temperature for water and record in Table 1 Sign is important! 10. Perform Data Analyses and Conclusions 2015 Catholic Initiatives in Math and Science, LLC All Rights Reserved 4
Lab Report for: NAME: Water Hex Screw Mass (kg) TABLE 1 Ti Tf ΔT ( o C) (Tf - Ti) 4186 J/kg o C Likely Identity Data Analysis: 1. Calculate the heat gained by the water using the calorimetry equation. Show work. 2. What is the value of the heat lost by the screw? Explain. 3. Using this information, calculate the specific heat of hex screw. Show work. 4. Using the specific heat of various steel blends, identify the type of steel the hex screw most likely is and the percent error. Record in Table 1. (J/kg- o C) (J/kg- o C) Aluminum 8.97 x 10 2 Silver 2.35 x 10 2 Barium 2.04 x 10 2 Steel, Mild 5.109 x 10 2 Lead 1.29 x 10 2 Steel, Stainless 430 4.605 x 10 2 Magnesium 1.023 x 10 3 Tin 2.28 x 10 2 Platinum 1.33 x 10 2 Tungsten Steel 1.339 x 10 2 Potassium 7.57 x 10 2 Zinc 3.88 x 10 2 2015 Catholic Initiatives in Math and Science, LLC All Rights Reserved 5