Calorimetry Lab Packet PDF

Calorimetry 1.0. Background: Calorimetry is a science of measuring the amount of heat involved in a chemical or physical process. Physical and chemical changes are typically accompanied by some form of energy change, known as heats of reaction (chemical) or heats of transition (physical). This en...

Calorimetry 1.0. Background: Calorimetry is a science of measuring the amount of heat involved in a chemical or physical process. Physical and chemical changes are typically accompanied by some form of energy change, known as heats of reaction (chemical) or heats of transition (physical). This energy change is usually observed as a flow of heat that enters or exits a system. Heat flow can be measured with a calibrated device called a calorimeter. A calorimeter is a container with insulated walls. The insulation prevents rapid heat exchange between the contents of the calorimeter and the surroundings. In the closed environment of the system, there is no loss or gain of heat. Because the change in temperature of the contents of the calorimeter is used to measure the magnitude of the heat flow, a thermometer is included with the calorimeter. The specific heat of any substance can be determined in a calorimeter. The specific heat is an intensive physical property of a substance and is the quantity of heat (in calories) necessary to raise the temperature of 1 g of substance by 1°C. The specific heats for some common substances are listed in Table 1. Notice that specific heat has the units calories per gram per degree Celsius. From Table 1, the specific heat of water is 1.00 cal/g °C; this means that it would take 1 cal to raise the temperature of 1 g of water by 1 °C. Table 1. Specific Heat Values for Some Common Substances In general, when a given mass of a substance undergoes a temperature change, the heat energy required for the change is given by the equation: Amount of heat = Q = SH (m) (ΔT) = SH (m) (Tfinal - Tinitial) where Q is the change in heat energy (amount of heat), SH is the specific heat of the substance, m is the mass of the substance in grams, and ΔT is the change in temperature (the difference between the final and initial temperatures); thus: Calories = (cal/g °C) (g) (°C) There are different types of calorimeters for specific functions, which is largely tied up with the reaction or process being studied. The basic principle behind calorimetry is the law of conservation of energy, which states that the energy of the universe (system + surroundings) is constant. Hence, the heat lost by a system is gained by the surroundings or vice-versa. Experimentally, the amount of heat absorbed by a known mass of water can be measured when a known mass of hot metal is placed in the water. The temperature of the water will rise as the temperature of the metal falls. Using the known heat capacity of water, the amount of heat added to the water can be calculated. This is exactly the amount of heat given up by the metal. Continue reading on the background of the experiment on pages 99-102 of Bettelheim and Landesberg (2012) (see section 6.0 reference). Activity 6: Calorimetry Page 2 of 10 2.0. Objectives: 1. To measure the heat capacity of the calorimeter. 2. To measure the specific heat of a metal. 3.0. Materials and Procedures: 3.1. Chemicals and Equipment: (*materials students should bring; **optional materials students may bring) Unknown metal Ring stand Stirring rod Electric calorimeter Test tube, 150x25 mm (x2) **Rubber mitts Thermometer, 200°C (x2) Beaker, 250-mL (x4) *Graphing paper/s Volumetric pipet, 25-mL Beaker, 500-mL (x2) *Distilled water Rubber aspirator Test tube holder (x2) *Labeller Thermometer clamp Tongs, beaker Test tube clamp Hot plate 3.2. BEFORE THE LAB SESSION: Complete the Pre-Lab submission (see Section 4). Each student must answer this individually and submit the lab notebook as instructed in the class announcement. Bring the designated materials for this experiment that are not available at the lab (this will be indicated per experiment). Watch this video to know how to use the electric calorimeter for this experiment: https://www.youtube.com/watch?v=TAiBB54DgcA 3.3. DURING THE LAB SESSION: Per group must check out the laboratory equipment/materials at the dispensing lab. Bring your IDs. You will always wear all PPE to lab. No PPE, no entry. Online students are required to participate and attend the lab through FLUX as all assessments will be the same. Follow the detailed procedures carefully (see section 3.5). After the activity, return all checked out materials and ensure that everything has been checked by the lab technician before claiming your IDs. DO NOT LEAVE the materials without the verification and approval of the lab technician. Follow all safety standards and proper disposal of wastes during and after the lab session. DO NOT leave your work area dirty/messy. 3.4. AFTER THE LAB SESSION: Complete the Post-Lab submission per group and submit together with your group report sheet (see Section 5). LJ Sanchez CHM031L All rights reserved. DO NOT SHARE NOR REPRODUCE. Activity 6: Calorimetry Page 3 of 10 3.5. Procedure: Determination of the heat capacity of the calorimeter Because the density of water is approximately 1.00 g/mL over the temperature range for this experiment, the amount of water used in all parts of the procedure will be measured by volume. With a 25-mL volumetric pipet, place 50.0 mL of water in a clean, dry 100-mL beaker; determine and record the mass (a1) Slowly heat the water with a hot plate to a temperature of 70 °C While the water is warming, you can do the following: with a 25-mL volumetric pipet, place 50.0 mL of cold water in the calorimeter cup; determine and record the mass (a2) Cover the calorimeter cup with the lid-thermometer-stirrer assembly. Stir the water for 5 min., observing the temperature during the time. Record the temperature for calorimeter calibration at 1-min. intervals (c) When the water warming in the 100-mL beaker has reached about 70 °C, remove the beaker from the hot plate and allow the hot water to stand for 2-3 minutes; stir the water occasionally during this time period. Then, quickly record the temperature to the nearest 0.2°C (a4), and pour the hot water completely into the calorimeter that has been assembled and has reached equilibrium Cover the calorimeter immediately and stir the contents gently for 30 seconds. Then, observe the temperature for 5 min. and record the temperature every 30 sec. during that 5-min. period (c). Make two (2) trials Plot the temperature as a function of time, as shown in Figure 1. Determine from your curve the maximum temperature by extrapolation and record it (a5). Determine the ΔT (a6 and a7). From the data, calculate the heat capacity of the calorimeter according to the calculations on the Data Sheet (a8-a12). LJ Sanchez CHM031L All rights reserved. DO NOT SHARE NOR REPRODUCE. Activity 6: Calorimetry Page 4 of 10 Determination of the specific heat of a metal With a 25-mL volumetric pipet, place 50.0 mL of cold water in a clean, dry calorimeter cup; determine and record the mass (b1) Obtain an unknown metal sample from your instructor. Record the number of the unknown on the Data Sheet (b) Weigh about 10 g of your unknown sample test and determine the mass to the nearest 0.01 g (b2). Pour the sample into a clean, dry test tube. Place the test tube in the water bath as shown in Figure 2. Be sure that all of the metal in the test tube is below the surface of the water. Heat the water to a gentle boil and keep the test tube in the bath for 10 min. Make certain that water does not splash inside the test tube. While the metal is heating, follow the temperature of the cold water for specific heat determination in the calorimeter for 5 min.; record the temperature on the Data Sheet at 1-min. intervals (c) After 5 min., record the temperature of the cold water to the nearest 0.2 °C on the Data Sheet (b3) After 10 min. of heating the metal, observe and record the temperature of the boiling water in the beaker to the nearest 0.2°C on the Data Sheet (b4). Obtain and use another thermometer for the calorimeter. All steps must be done quickly and carefully at this point to avoid cooling. Remove the test tube from the boiling water; wipe the drops of water that will cling to the outside glass of the test tube with a paper towel; remove the lid on the calorimeter; add the hot metal to the calorimeter. Be careful that no water is added to nor lost from the calorimeter during the transfer. Record the calorimeter temperature as soon as the lid has covered the calorimeter cup. Note the time when the temperature is determined (c) Stir the water to ensure full heat exchange. Continue to follow the temperature, recording the temperature on the Data Sheet every 30 sec. for the next 5 min. (c) Make two (2) trials Plot the temperature as a function of time, as shown in Figure 1. Determine from your curve the maximum temperature; record the temperature on the Report Sheet (b5). Determine the ΔT (b6). From the data, determine the specific heat and the atomic mass of the metal (b7 to b11). LJ Sanchez CHM031L All rights reserved. DO NOT SHARE NOR REPRODUCE. Activity 6: Calorimetry Page 5 of 10 Figure 1. Plot of temperature versus time (Lifted from Bettelheim & Landesberg, 2012). Bunsen burner will be replaced with a hot plate for this experiment Figure 2. Water bath assembly for heating the metal (Lifted from Bettelheim & Landesberg, 2012). LJ Sanchez CHM031L All rights reserved. DO NOT SHARE NOR REPRODUCE. Activity 6: Calorimetry Page 6 of 10 3.6. Data Sheet a. Determination of the heat capacity of the calorimeter: # Measurement Trial 1 Trial 2 Mass of the warm water, g 1 (50.0 mL x 1.00 g/mL) Mass of the cold water, g 2 (50.0 mL x 1.00 g/mL) Temperature of the equilibrated system, °C: 3 cold water and calorimeter 4 Temperature of the warm water, °C 5 Maximum temperature from the graph, °C ΔT of cold water and calorimeter, °C 6 (#5) – (#3) ΔT of warm water, °C 7 (#5) – (#4) Heat lost by warm water, cal 8 (#2) x 1.00 cal/g °C x (#7) Heat gained by cold water and the calorimeter, cal: 9 -(#8) Heat gained by cold water, cal 10 (#1) x 1.00 cal/g °C x (#6) Heat gained by the calorimeter, cal 11 (#9) - (#10) Heat capacity of calorimeter (Ccal ), cal/°C 12 (#11) / (#6) b. Determination of the specific heat of a metal: # Measurement Trial 1 Trial 2 Mass of cold water, g 1 (50.0 mL x 1.00 g/mL) 2 Mass of metal, g 3 Temperature of the equilibrated system, °C: Temperature of hot metal, °C 4 (Temperature of boiling water) 5 Maximum temperature from the graph, °C ΔT of cold water and calorimeter, °C 6 (#5) – (#3) Heat gained by the calorimeter and water, cal: 7 [(#1) x 1.00 cal/g °C x (6)] + [Ccal x (#6)] ΔT of the metal, °C 8 (#5) – (#4) 9 Heat lost by the metal, cal: -(#7) Specific heat of the metal, cal/g °C 10 (#9) / [(#2) x (#8)] Atomic mass, g/mole 11 6.3 cal/mole °C / (#10) Unknown number ______________ Metal unknown identity ______________ LJ Sanchez CHM031L All rights reserved. DO NOT SHARE NOR REPRODUCE. c. Temperature Data Sheet: Trial 1: Trial 2: Activity 6: Calorimetry Page 8 of 10 d. Data Plot LJ Sanchez CHM031L All rights reserved. DO NOT SHARE NOR REPRODUCE. Activity 6: Calorimetry Page 9 of 10 4.0. Pre-Lab Submission (Individual- 15 pts.) You must answer the Pre-lab questions below in your lab notebook before our laboratory session. All parts of the Pre-lab must be handwritten in ink and legible. Include the following as part of your pre-lab assignment: 1. Heading format per page: Experiment number and title, date of the experiment, your name, group number, course code and section, and page number (2 pts.) 2. Purpose of the experiment (2 pts.) 3. Pre-lab questions (11 pts.) Experiment 3 Pre-Lab Questions: 1. What is the purpose of the insulated walls in a calorimeter? (2 pts.) 2. Why is a thermometer included in the construction of a calorimeter? (2 pts.) 3. What are the units of specific heat that we will use for this experiment? (1 pt.) 4. If you were to construct benches for a stadium that would be in the sun for long periods of the day, excluding cost as a factor, why would you choose wood over aluminum or iron? (2 pts.) 5. A car engine cools efficiently when water is used as a coolant, but the engine does not cool as efficiently with either pure ethylene glycol (antifreeze) or pure ethyl alcohol. Explain this observation. (2 pts.) 6. 50 g of water was heated from 20 to 50°C. How many calories were needed to bring about the temperature change? Show your solution. (2 pts.) LJ Sanchez CHM031L All rights reserved. DO NOT SHARE NOR REPRODUCE. Activity 6: Calorimetry Page 10 of 10 5.0. Post-Lab Submission (Individual- 10 pts.) You must complete the post-lab questions below and submit together with your report sheet at the end of the experiment. Everything written in your report and post-lab sheet must be legible and handwritten IN INK. Deduction of points will be implemented as necessary for wrong formats. Post-Lab Questions: 1. In doing this experiment, a student did not follow the directions exactly. How would the experiment be affected if the following were done? (2 pts.) a. Not all of the 50 mL water was delivered from the volumetric pipet to the calorimeter. b. No plot of temperature was carried out. Instead, the student used the value of the water just after mixing with the metal as the maximum temperature. 2. Calculate the amount of heat (in calories) absorbed when 50.0 g of water at 20°C spreads over your skin and warms to body temperature, 37°C. Show your work. (2 pt.) 3. A 102.5-g sample of metal beads was heated in a water bath to 99.5°C. The metal was then added to a sample of water (25.7 g) and the temperature of the water changed from an initial temperature of 20.0°C to a final temperature of 41.5°C. a. What was the temperature of the metal at equilibrium? (1 pt.) b. What was the temperature change of the metal? Show your work. (2 pt.) c. Calculate the specific heat and the atomic mass of the metal. Show your work. (2 pts.) d. What is the metal? (1 pt.) 6.0. Reference Bettelheim, F. A., & Landesberg, J. M. (2012). Laboratory Experiments for Introduction to General, Organic and Biochemistry (8th ed.). Cengage Learning US. https://bookshelf.vitalsource.com/books/9781133711858 LJ Sanchez CHM031L All rights reserved. DO NOT SHARE NOR REPRODUCE.