Student note : need lab report I need a post lab document. Having the graphs and data required plus the answer of the post lab questions. We need to do the graph in Excel The graphs, tables and post lab qs should be based on the observation pictures/n Laboratory #4: Thermometric and Potentiometric Titration of an Unknown Hydrochloric Acid Solution I. Pre-Laboratory Assignment Read Chapter X in "Laboratory Handbook for General Chemistry", view the pre-lab video and read the laboratory procedure (below). Write an objective (paragraph form) and procedure (flowchart) for this lab. Answer the following questions in you laboratory notebook: What is the reaction you will study during the thermometric titration and the potentiometric titration? 1. Explain in your own words how you will determine the equivalence point of the thermometric titration. Draw a picture to illustrate. 2. 3. What is KHP and how will it be used in this experiment? Include a Lewis structure and balanced chemical equation. II. Laboratory Procedure Part A. Preparation of a Standardized NaOH (aq) solution 1. Calculate and weigh out the necessary amount of solid NaOH required to make 150 mL of 1.50M NaOH (aq) solution. When weighing the NaOH, there is no need to strive to perfection because you will standardize this solution later to determine its exact concentration. 2. Transfer the NaOH to a 250 mL Erlenmeyer flask and add 150 mL of distilled water from a graduated cylinder. Stir until the NaOH dissolves and be sure to seal the flask whenever it is not in use. This is your NaOH (aq) stock solution. CAUTION: NaOH (aq) is caustic. 3. Prepare a dilution of your ~1.5M NaOH solution transferring 5.00 mL of the solution with a volumetric pipet to a 50 mL volumetric flask. THIS MUST BE DONE WITH BOTH ACCURACY AND PRECISION. Dilute the solution to the line with distilled water and mix well. Repeat this procedure two additional times so that you have 3 solutions of diluted NaOH (aq) that is approximately 0.15M. 4. You will standardize your solutions by reaction with Potassium acid phthalate, KHP. KHP reacts with NaOH in a 1-to-1 fashion according to the following equation. Calculate and weigh out the correct amount of KHP (mw 204.23 amu) required to react stoichiometrically with 10.0 mL of your diluted NaOH (aq) solutions that are approximately 0.15M. Be sure to record the mass of KHP to 3 decimal places. Add the KHP to a small beaker. Repeat this 2 additional times so that you have 3 beakers with KHP in them. Label each beaker so you know the mass of KHP in each beaker and record this in your notebook by setting up a table like the one below. 38 Beaker Mass KHP (g) Moles KHP Titration Volume ~.15M NaOH True concentration of NaOH (aq) 5. To each beaker containing KHP add 50 mL of distilled water and a stir bar to dissolve the KHP. Once dissolved, add 2 drops of phenolphthalein indicator to each beaker as well. 6. After rinsing your buret with a few mL of one of the 50mL NaOH solutions that are approximately 0.15M, fill the buret with the same NaOH solution. 7. Titrate one of the KHP solutions with the NaOH solution in the buret until the solution in the beaker turns faint pink. This is the equivalence point, where the moles of NaOH added are equal to the moles of KHP initially present. Record the volume of NaOH required for the titration. 8. Repeat this 2 additional times for the 2 remaining beakers. Use a different NaOH solution for each titration. 9. Determine the average concentration of the NaOH STOCK SOLUTION from your data. (You may do this at the end of the lab if you are running behind). Part B. Potentiometric titration of an unknown hydrochloric acid solution 1. Add exactly 20.00 mL of HCI (aq) solution to a 100 mL beaker with stir bar. 2. Fill you buret with your ~1.5M NaOH (aq) stock solution. Be sure to rinse the buret with a few mL of the solution first. 3. Open Logger Pro. Place the pH electrode into your beaker containing the HCI (aq) solution. Set up a table in you notebook to record the volume of NaOH (aq) added and the pH. 4. Titrate the HCI (aq) solution with your NaOH (aq) solution by adding a small amounts of your NaOH (aq) solution from the buret. Be sure to note initial volume on the buret and the final volume on the buret after addition of an aliquot. Record the volume added and the pH both in Logger Pro and in your notebook. 5. Continue to add small aliquots until your pH is over pH = 9. 6. The equivalence point should be around pH=7.0 and reflect a maximum in the d(pH) plot, and a zero of the d(dpH) plot. 39 Part C. Thermometric titration of an unknown hydrochloric acid solution 1. Add exactly 20.00 mL of HCI (aq) solution and stir bar to a thermos. 2. Fill you buret with your ~1.5M NaOH (aq) stock solution. Be sure to rinse the buret with a few mL of the solution first. 3. Unplug the pH electrode from channel 1 on the port hub. Plug in the temperature probe to channel 1 on the port hub. Open Logger Pro. Insert tip of the buret into one of the openings on the rubber stopper of the thermos. Insert the thermocouple probe into another opening so it is immersed into the Hydrochloric Acid solution. Set up a table in you notebook to record the volume of NaOH (aq) added and the temperature of solution. 4. Titrate the HCI (aq) solution with your NaOH (aq) solution by adding about 3 mL of NaOH (aq) solution from the buret at a time. The temperature of the solution will go up with each addition until the equivalence point is reached. Be sure to note initial volume on the buret and the final volume on the buret after addition of each aliquot. Record the volume added and the maximum temperature achieved after each addition both in Logger Pro and in your notebook. 5. Continue to add small aliquots until you have enough data to determine the maximum overall maximum temperature achieved by the solution. This means you must titrate past when the temperature stops increasing. 6. Transfer your data to excel and plot a graph of temperature against the total volume of base added. Use extrapolation of the two sections of the graph to deduce the maximum temperature reached without heat loss. This will be your equivalence point. III. Post-Laboratory Questions Turn in your sheets at the end of the period. Answer the following questions in your laboratory notebook and upload scans of your notebook pages along with any graphs etc. Uploads are due 48h after the end of the experiment (sabbath excluded). 1. What is the concentration of your standardized NaOH (aq) stock solution? 2. What is the concentration of the unknown HCI solution as determined by potentiometric titration? 3. What is the concentration of the unknown HCI solution as determined by thermometric titration? 4. What are the major sources of error in each part of the experiment? Which method of titration yielded more accurate results? Which yielded more precise results? Explain. 40

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