Text reference: Sections 10.2, 10.3 On a sunny day, the water in a swimming pool may warm up a degree or two while the concrete around the pool may become too hot to walk on in your bare feet. This may seem strange because both the concrete and the water are being heated by the same source--the sun. This evidence suggests it takes more heat to raise the temperature of some substances than others. This, in fact, is true: the amount of heat required to equally raise the temperature of equal masses of different substances depends on what the substances are. The amount of heat that is required to raise the temperature of 1 g of a substance by 1 Celsius is called the specific heat capacity, or simply the specific heat, of that substance. Water. for instance, has a specific heat of 1.0 cal/(g C). This value is high in comparison with the specific heats for other materials, such as concrete. In this experiment, you will use a simple calorimeter and your knowledge of the specific heat of water to determine the specific heat of lead. Measure the specific heat of lead. Identify an unknown metal from its specific heat (optional), safety goggles 1 50-mL beaker 1 250-mL beaker 1 400-mL beaker 1 lo0-ml graduated cylinder 1 large test tube 1 glass stirring rod 1 utility clamp 1 ring stand 1 ring support 1 wire gauze 1 gas burner 8 centigram balances/class 1 plastic-foam cup 1 thermometer The Specific Heat of a Metal a9
lead shot, Pb ~ unknown metal distilled water Note the Safety Symbols used here and in the Procedure section view safety information on pages 7-10. o #Aways wear safety goggles when working in the lab. Lead is a toxic metal. Wash your hands thoroughly after use. Mercury is extremely toxic, and mercury spills are very difficult to clean up. If you should break a mercury thermometer, immediately report the incident to your teacher. Copy Table 15.1 into your laboratory notebook. As you perform the experiment, record your data in this table. 1. Heat 250 ml of water in a 400-mL beaker, until it is boiling gently. 2. While the water is heating, determine the mass of a clean, dry 50-mL beaker to the nearest 0.01 g and record. Add between 80 g and 120 g of lead shot to the beaker. Measure the combined mass of the beaker and lead to the nearest 0.01 g and record the measurement. 3. Transfer the lead shot to a large, dry test tube. Use the utility clamp to suspend the test tube in the boiling water as shown in Figure 15.1. The lead shot should be below the level of the water in the beaker. Leave the test tube in the boiling water bath for at least 10 minutes. 4. While the lead shot is heating, measure 100 ml of distilled water in a graduated cylinder. Pour the water into a plastic-foam cup, and place the cup in a 250-mL beaker for support, as shown in Figure 15.2. 5. Measure and record the temperature of the water in the plastic-foam cup and of the water in the boiling bath. Experiment 15
Re- 6. Remove the test tube from the boiling water and quickly pour the lead shot into the water-filled plastic-foam cup. Place a thermometer and a glass stirring rod into the cup. Use the stirring rod to gently stir the lead shot. Do not stir the shot with the thermometer. Note the temperature frequently, and record the maximum temperature reached. 7. Pour the water off, and return the lead shot to your teacher. B. (Optional) Follow the same procedure to determine the specific heat of an unknown metal. :lean ~port
Bat Table 15.1 Data Trial mass of 50-mL beaker mass of 50-mL beaker + lead shot mass of lead shot initial temperature of water in cup initial temperature of lead shut (temperature of boiling water~ maximum temperature of lead + water mass of water 1. Determine the changes in temperature of the water (ATw~ter) and of the lead shot (ATlead) for each trial. 2. Calculate the heat gained by the water in each trial. 3. Remembering that the heat gained by the water is equal to the heat lost by the lead, calculate the specific heat of lead for each trial. 4. Calculate the average value for the specific heat of lead in your experiment. 5, If you tested an unknown, repeat these calculations to determine the specific heat of the unknown metal, Conc usjons 1. Calculate the percent error in the specific heat value that you determined experimentally, Use the accepted value given by your teacher. percent error = laccepted... value - experimental valuel accepted value 100 percent ~2 Experiment 15
Trial 2 2. You assumed that the initial temperature of the lead shot was the same as that of the boiling water. If the lead shot was actually at a lower temperature than the water, how would your value for the specific heat be affected? 3. Identify other possible sources of error in this experiment. 4. Compare your value for the specific heat of lead to the values obtained by your classmates. Can specific heat be used to identify substances? 1. Design experiments to determine the specific heats of ethyl alcohol, methyl alcohol, and oil. r (ATwater) and of equal to the heat ~ch trial. : of lead in your ~ to determine the ue that you deteryyour teacher. el x I00 percent The Specific Heat of a Metal 93