Specific Heat Capacity Lab Adapted from ChemCom by Dr. G. Maynes Introduction: In our study of the heat produced by exothermic reactions, we determined the molar heat of combustion of several fuels. To do this we used calorimetry, and made use of the relationship q = Cp * m * ΔT and the “given” that the specific heat capacity, Cp, for water is 4.18 j/oCg. In this lab we will again use calorimetry, and by comparing the impact of a specific exchange of heat on the ΔT of water and an ”unknown” metal sample, we will attempt to identify the metal. Specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius. Safety: goggles and closed-toe shoes; be careful of hot liquids and metals. Procedure: 1) Determine an accurate mass for your sample of metal. Note the observable physical properties of the metal. 2) Gently put your metal sample into ~ 250 mL of water in a 400 or 600 mL beaker, and heat this to boiling on a hot plate. Monitor the water temperature with a glass thermometer. 3) Assemble a calorimeter from a double Styrofoam cup with a cardboard cover; insert the metal stem of a digital thermometer into the cover. (See diagram next page). Weigh the cups. 4) Put ~ 100 mL of cold tap water into the calorimeter, and allow the temperature to settle. Record the temperature and the exact mass (that is, weigh it) of the water. 5) Wait until the water in the beaker has been boiling at a stable temperature for 5 minutes. Grasp the metal sample firmly with your crucible tongs, and quickly transfer it to the calorimeter, put the top with the digital thermometer back in place, and begin observing the temperature of the water in the calorimeter. 6) Record the temperature of the water in the calorimeter every 30 seconds until you have recorded the same value 4 times in a row, or until the temperature starts to fall. Make this your digital thermometer, not a glass one Calculations: 1) Determine the heat absorbed by the water in the calorimeter q = Cp*m*ΔT 2) Using the same formula, plug in the value for q to what you calculated above. Use the mass of the metal and the ΔT for the metal so that the Cp for the metal is the only unknown, and solve for Cp.. 3) Using the data in the table on the next page, your observations of the physical characteristics of the metal and your common sense, identify the metal. Material Aluminum Brass Copper Gold Iron Lead Silver Stainless Steel Zinc Granite Air Water Specific heat, Cp 0.895 0.380 0.387 0.129 0.448 0.128 0.233 0.51 0.386 0.803 1.00 4.18 Questions: 1) What is your metal? Why do you say so? 2) What do you see as sources of error? Be thorough. 3) Closely related to sources of error, what assumptions did you have to make for your experiment to work? 4) Why did we put your metal in boiling water? Exactly why – not “to get it hot”. Why not heat it some other way? 5) Why did we have separate thermometers? Why not just move the thermometer from the heating bath to your calorimeter? (Think of two good reasons). 5) Would you use determination of Cp as a way to identify a metal? Why or why not? 6) On a sunny day, beach sand gets very hot, a grassy area is comfortable, and the water is cool. Using the data above and what you have learned in this lab, along with your common sense, explain why.