Laboratory 6 Procedure – Specific Heat Capacity of Unknown Substances CHE-121: Principles of Chemistry 1 Part 1: This week’s laboratory assignment is an extension of the concepts we learned about solubility and thermochemistry. The general rule of thumb for the dissolving of chemical compounds in water is that they will readily release heat during the process. Though, there are some compounds like potassium chlorate that respond endothermically during the dissolution process. Even more interesting is that some compounds like cerium(III) sulfate have a higher solubility at lower temperatures. Your initial post to the forum should be in response to the following: Discuss the relationship between solubility and temperature. Here are some suggestions of topics on which to elaborate upon in your explanations: • • • Give real-world examples of the effect of heat on solubility. Rationalize the relationship (if any) between endothermic/exothermic reactions and solubility. Discuss the dependence of solubility on temperature. Your subsequent four posts to your peers and/or your instructor should further the discussion by elaborating on the objectives above. Do not include any results for your laboratory experiments. References must be provided for any content retrieved from credible sources. Part 2: Background: This week, you will be tasked with investigating and determining the specific heat capacity of an unknown substance. Recall, the specific heat capacity (c) of a substance, commonly called its “specific heat,” is the quantity of heat required to raise the temperature of 1 gram of a substance by 1 degree Celsius (or 1 kelvin). Mathematically, we compute the specific heat of a substance using the following equation: 𝑐= q 𝑚Δ𝑇 Page 1 of 7 Laboratory 6 Procedure – Specific Heat Capacity of Unknown Substances CHE-121: Principles of Chemistry 1 In this equation, q is the absorbed heat, m is the mass of the substances, and ΔT is the change in temperature. Specific heat is an intensive property meaning that it depends on the type of substance and not the amount. Liquid water has a relatively high heat capacity (4.184 J/g∙°C) in contrast to that of most metals whose heat capacities are often less than 1 J/g∙°C. This is explains why it doesn’t take long for a saucepan to become hot, but the water takes much longer to start boiling. The table below lists the heat capacities of some commonly encounter substances. Substance Symbol (State) Specific Heat (J/g∙°C) Water Aluminum Iron Copper Gold H2O(l) Al(s) Fe(s) Cu(s) Au(s) 4.184 0.897 0.449 0.385 0.129 There is a single, primary objective of this lab: to determine the specific heat of two unknown compounds. To do this, you will be provided with basic procedural instructions to set up the lab, but it will be up to you to determine the steps needed to collect data and compute the specific heats. Before you start this laboratory assignment, you are encouraged to review the content covered in Chapter 5 of the textbook. Throughout this laboratory assignment, you will be required to perform and thoroughly document your data and calculations. Be sure to record all observations and any relevant notes that you think you will need to include in your laboratory report; refer to the end of this document for information that must be included in your final report. Page 2 of 7 Laboratory 6 Procedure – Specific Heat Capacity of Unknown Substances CHE-121: Principles of Chemistry 1 Procedure: Lab Scenario Imagine that you are working as an analytical chemistry is a multibillion-dollar chemical corporation that consults with major companies in the global automotive industry. Your lab team has been tasked with developing and investigating the properties of two potential coolants and comparing them to that of the conventional ethylene glycol coolant. The two coolants, Coolant Y and Coolant A, have the potential to revolutionize the automotive industry in that they would more efficiently dissipate heat and they would be significantly cheaper. Your task is to determine the specific heats of both coolants and report your findings in a formal report. Preparing the Lab I 1. From the course home page, access the lab environment by clicking on the Virtual Lab link. 2. After the lab environment loads, click ‘File’ then ‘Load an Assignment.’ 3. Select the ‘Thermochemistry’ category. 4. Select the ‘Coolant I’ assignment. 5. At this point, you have prepared the laboratory for the experiment with the required supplies to complete your experiment. Performing the Experiment I 6. Before beginning the experiment, draft a hypothesis (to be included in your report) of your expected outcome(s). 7. Begin by placing 3.0-L container of H2O and Compound Y on the workbench. Also acquire a foam cup, 250-mL beaker, a Bunsen burner, and a balance from the stockroom. 8. Transfer 150 mL of water to the beaker. Heat the water to 100°C by placing the flack atop the Bunsen burner. We will assume that no heat will be lost while heating the beaker, so you will need to ‘insulate’ the glassware. Right-click the beaker and select ‘Thermal Properties’ from the menu, then check the box for ‘Insulate from surroundings.’ Move the beaker back to the workbench after it has heated. 9. Next, you will prepare the calorimeter (foam cup) for measuring the change in temperature when the substances are combined. Determine the mass of 25.0 mL of Compound Y using the foam calorimeter and balance and record this in your notes or the Page 3 of 7 Laboratory 6 Procedure – Specific Heat Capacity of Unknown Substances CHE-121: Principles of Chemistry 1 data table, then move the cup to the workbench. 10. Ensure that you have recorded the initial temperatures of the water and Compound Y before continuing to the next step. 11. Combine the substances by pouring 25.0 mL of water into the calorimeter and record the final temperature in your notes. Also record the mass of the water assuming a density of 1.00 g/mL at 100°C. 12. Repeat steps 6-11 using 30-mL amounts of water and Compound Y and record your all data for the second trial. Preparing the Lab II 13. After the lab environment loads, click ‘File’ then ‘Load an Assignment.’ 14. Select the ‘Thermochemistry’ category. 15. Select the ‘Coolant II’ assignment. 16. At this point, you have prepared the laboratory for the experiment with the required supplies to complete the second experiment. Performing the Experiment II 17. Before beginning this experiment, draft a hypothesis (to be included in your report) of your expected outcome(s) for the second experiment. 18. Repeat steps 1-11 of the lab to collect data to determine the specific heat capacity of Compound A. 19. Verify that you have collected all of the necessary data to compute the change in temperature, the heat lost by the water, and the specific heat of the compounds for all trials. Page 4 of 7 Laboratory 6 Procedure – Specific Heat Capacity of Unknown Substances CHE-121: Principles of Chemistry 1 Notes This section should include notes about any observations or data collected during the lab. Begin typing here. Page 5 of 7 Laboratory 6 Procedure – Specific Heat Capacity of Unknown Substances CHE-121: Principles of Chemistry 1 Data This section will include all data collected during the lab. Compound Y mc(g) mw(g) Tc,initial (°C) Tc,final (°C) Tw,initial (°C) Tw,final (°C) ΔTc (°C) ΔTw (°C) -qw (J) Cp,c (J/g°C) ΔTc (°C) ΔTw (°C) -qw (J) Cp,c (J/g°C) Trial 1 Trial 2 Compound A mc(g) mw(g) Tc,initial (°C) Tc,final (°C) Tw,initial (°C) Tw,final (°C) Trial 1 Trial 2 Variables: mc Mass of unknown substance mw Mass of water Tc Temperature of unknown substance Tw Temperature of water -qw Heat lost by water Cp,c Specific heat of unknown substance *Note: You can copy and paste your data table into your report later. Page 6 of 7 Laboratory 6 Procedure – Specific Heat Capacity of Unknown Substances CHE-121: Principles of Chemistry 1 Report Requirements This section contains key information that must be included in your typed report. 1. Define and discuss the problem/goals in a manner that is clear and insightful. 2. Identification of the strategies/procedures used during the lab. 3. Clear hypothesis statement and other potential solutions that identify any relevant contextual factors (i.e. real-world costs). Consider any potential limitations of conducting the experiments in a real laboratory. 4. Clear presentation of data including any tables or other figures that are relevant to understanding your stated conclusions at the end of the report. The following items are required in your report: a. Data table b. Documentation of all required calculations. 5. Clearly stated results (evidence of specific heat capacities) and discussion possible improvements to the procedure. 6. Conclusive statements arguing in favor of your findings. Note: All reports will be graded using the rubric embedded within the course. Here are some questions to consider as you write your report: 1. 2. 3. 4. 5. 6. Does my problem statement make sense? Have I summarized my strategies/procedures well enough to be replicated by an outsider? Did I have a valid hypothesis at the start of the lab? Have I expressed this in my report? Do my tables and/or graphs make sense? Are my conclusions valid based on my supplied data? Did I thoroughly summarize my laboratory experience in a concise, factual way such that the reader can understand my processes and findings in the conclusion section alone? Page 7 of 7
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