In lab, you will calibrate the calorimeter using two trials and potassium chloride (KCl) as the calibration standard. Then you will measure the heat released upon dissolution of three salts: anhydrous sodium acetate, hydrated sodium acetate, and sodium chloride (NaCl). Preparing the instrument and sample Load solvent in the calorimeter: Prepare a large flask with ultrapure water and allow it to come to room temperature. The calorimeter's Dewar flask has a capacity of approximately 100 mL and must be filled with not less than 90 mL but not more than 120 mL of solvent. Use a volumetric 100.00 mL pipet to transfer 100.00 mL of ultrapure room temperature water into the Dewar flask. *Volumetric pipets are "Class A" glassware, and the errors associated with their measurements can be found either on the flask itself or in a table of tolerances ( like this one, click ). Loading samples into the rotating cell: It is extremely important that you fill the cell carefully and that no sample is lost or place in the incorrect place in the sample dish. If you do spill some of the sample, or if the cell leaks, clean out the cell and start again. Loading by weight (solid or liquid samples): Disassemble the cell and tare the clean and dry bottom of the cell (a Teflon dish) on an analytical balance. Take the Teflon dish out of the balance and add the solid sample directly to it. Weigh the dish plus sample to obtain the sample mass. Loading by volume (liquid samples): Liquid samples can be loaded into the rotating cell either by volume or by weight. Disassemble the cell and tare the clean and dry bottom of the cell (a Teflon dish) on an analytical balance. Set the Teflon dish on a flat surface and press the glass bell over the dish, handling the glass carefully as described above. Fill the pipet with the solution to be added. Carefully insert the pipet through the glass stem and add the solution to the rotating cell. Assembling the sample cell, cover, pulley assembly and push rod: Carefully assemble the sample cell by pressing the glass bell over the dish. To do this, place the dish on a flat surface and gently press the glass bell over the dish to assemble the cell. Do not hold the thin-walled glass stem during this operation–it is fragile and will break easily. Insert the stirring shaft (metal rod) through the cover assembly, and attach it to the cell assembly by sliding the white plastic coupling of the sample cell onto the metal shaft as far as possible. Tighten the thumb screw until it is finger tight. Insert the glass push rod very carefully and avoid disturbing the sample. With the dish again on a flat surface, insert the push rod through the pulley hub and gently press the end of the rod into the socket in the sample dish. When the entire assembly is prepared with sample, the thermistor probe can be placed in the hole in the sample cover and the entire assembly can be placed onto the calorimeter so that sample cell is lowerd into the Dewar flask with the cover in place on the air can. Experimental Procedure Set up the calorimeter Switch on the Calorimetric Temperature Unit using the on/off switch at the rear left of the instrument. After a short "Self Test" routine the following screen will appear. Press Operating Controls . Look over the buttons. Method of Operation should be Solution and Language should likely be English . Standardize the calorimeter with KCl (to determine \(C_p\)) The purpose of this standardization is to determine the heat capacity of the calorimeter (\(C_p\)) by measuring the heat change in a well-characterized reaction. You will use the dissolution of KCl as the calibration standard. In the recommended standardization procedure, when 0.5000 –0.7000 grams of KCl is dissolved in 100.00 mL of DI water, the reaction absorbs 230.98 joules per gram of KCl at 25 ̊ C . Note The KCl used in the calibratio should be oven-dried overnight at 80˚ C and cooled in a desiccator prior to use. Exposure of the KCl to air and moisture should be avoided in order to preserve the integrity of the standard. Please return the KCl stock container to the desiccator immediately after use. If you have not done so already, add exactly 100.00 ± 0.08 mL of ultrapure water to the Dewar flask. Prepare the sample cell cover, pulley assembly and push rod as described above. Make sure that both components of the rotating cell (Teflon dish and glass bell) are clean and dry before use. Be sure the bell jar is sealed against the teflon dish. Weigh 0.5000 –0.7000 gram of your standard KCl into the clean, dry Teflon dish on an analytical balance to an accuracy of ± 0.0001g(or ± 0.0002 g, depending on the balanced used). Place the thermometer into the hole in the cover assembly, making sure not to distrub the cell. Place the sealed sample cell into the Dewar (with water) so that the cover is in place over the calorimeter air can and the thermistor probe cord is moved out of the way of the pulley assembly. Place the lead donut on the cover. Place the drive belt over the pulleys. On the calorimeter, press Escape or Main Menu to go back one screen to the main menu. Press Diagnostics . The Data Logger should be off. If it is on, press the Data Logger button to turn it off . Press the Delete Data Log File button to clear the data log. Check to be sure that the Data Log Format is set to Data Format (csv) . Press the Start button on the right side of the screen. The stirrer to the calorimeter should turn on automatically. You will be prompted to enter a Sample ID. If you like, use the format: initialsMMDD-N, where: initials are your initials; MMDDis the date; and, N is the number of the run (e.g., 1 for the first run). Press Enter when you are done. Press the Data Logger button to turn data logging on . At this point your run has started and you are logging temperature and time data. Press the Main Menu button on the right side of the screen. Then press Calorimeter Operation . You will be taken to a screen that shows the progress of the current run. You will see your sample run information along with the temperature inside the system (listed as the Bucket Temperature). At the bottom of the screen you will see a timer that will monitor the progress of the run. Press the Temperature Graph button and a real-time image of the temperature inside the calorimeter (the Bucket Temperature) will appear. Press Setup and you will see the following screen. Set the Bucket Min value ~0.4 degrees below the pre-period baseline temperature and Bucket Max value ~0.4 degrees above the pre-period baseline temperature. Press Escape when you are done. Go to the computer associated with the calorimeter. On the desktop, find the Parr Calorimeter shortcut. This will take you to a Web page associated with the calorimeter. Once there, click on the LCD Image tab and a screen shot of what is currently on the calorimeter display will appear. This is not a “living” image, but one that is captured at the moment you clicked the LCD Image button. To update the image, press the F5 key on the computer keyboard. About seven minutes after starting the run you will hear a loud beep and the calorimeter will prompt you to “inject” the solid sample into the stirring solution. Do this by gently, but firmly, pushing down on the glass rod (NOTE: these are easily broken so please be careful). Then, press continue on the calorimeter. "Timed out" error If the calorimeter gives a "Timed out" error message, it likely means that the temperature was not stable during the first seven minutes. If this happens, check the bell jar to be sure it is assembeld correctly. If so, start the run again. If not, begin again by preparing a new sample. Observe the temperature change inside the system by monitoring the Temperature Graph either on the calorimeter display or by updating the LCD Image on the computer screen. You want to watch the display for the first minute or two to be sure that the sample was, in fact, introduced properly into the solvent. If there was a problem with the mixing of solute and solvent (something that happens occasionally) you will get an error message on the calorimeter screen and the run will stop. If that happens clean out the system and try the run again. Near the end of the run you will hear another beep from the calorimeter telling you the run has completed. Press F5 on the screen and capture the Temperature Graph on the computer screen at that moment. Right-click on the thermogram image and save a copy to your data folder on the computer. Bring up the report for the run save a copy of it as an image file. Click on the Home button at the bottom of the browser window. Then Click on the Data Log tab. You will get a new window containing the logged data from the run. Each row contains the date, the time, the bucket temperature, the jacket temperature and two columns that are mostly zeros. Use Control-A to select the entire window; and, Control-C to copy it. Open the Windows Notepad (Start ®Accessories ®Notepad) and Paste the data log into the Notepad window. Delete any text that may appear below the last row of data. Select Save As from the File menu and save the Notepad as a .txt file into your data folder. Press Escape on the calorimeter screen and the report will disappear leaving the thermogram. Press Escape again and you will return to the Calorimeter Operation Screen. Press Main Menu on the button bar and then press the Diagnostics button to navigate back to the Diagnostics Screen. Press the Data Loggerbutton and when you get to the Data Logger screen andturn the Data Logger off. Ask your TA to supervise as you carefully dismantle the calorimeter. First remove thermistor probe and wipe it dry. Then remove the glass push rod, wipe it dry and place it somewhere where it will not get broken. Carefully lift the cell assembly part way out of the Dewar flask and carry both the Dewar flask and the cell assembly over to the sink. Rinse the cell assembly briefly and then remove the cell from the shaft. Rinse the Dewar and the Teflon dish. Be extremely careful not to break the glass pieces –the glass cell costs ca. $135 and the glass push rods cost ca. $60 each. Carefully dry the cell, inside and out and even up into the shaft. Dry also the Teflon dish, the Dewar, and the pieces of the top (metal shaft and top). Also, check the calorimeter and clean up any spills inside the aircan or on the surface of the calorimeter itself. Repeat the procedure with another sample of the calibration standard, and then once with each of the other samples. File Names Use the following convention when naming all files: initialsMMDD-N, where N is the number of the run (e.g., 1 for the first run).When naming files number each run according to the following table: File name initialsMMDD-N Description initialsMMDD-1 First calibration with KCl initialsMMDD-2 Second calibration with KCl initialsMMDD-3 Sodium acetate initialsMMDD-4 Sodium acetate trihydrate initialsMMDD-5 Sodium chloride Repeat the procedure for all samples The general steps are listed below: Pipet 100.0 mL of water into the Dewar flask. Weigh accurately 0.7 -0.8 grams (weigh to nearest 0.0002 g) of solid sample into the Teflon dish. Assemble the apparatus as before. Conduct the runs exactly as you did during the standardization. Repeat this procedure for remaining salts.