You should secure the calorimeter within a 400-mL beaker. Place the lid on the calorimeter. Turn on the switch that controls the stirring mechanism and stir the water at a moderate speed. 4. Clamp the temperature probe to the ring stand and then carefully lower it through the hole in the lid. Adjust the height so that the probe is in the water but does not touch the magnetic stirrer bar. 5. Weigh out 6.00 – 7.00 g of lithium chloride, LiCl, using a top loading balance, and record the mass in your lab notebook. Keep the LiCl on the weighing paper on the lab bench and in secure place. 6. Tap the green arrow, , in the lower left of the screen to start data collection. The screen should display this after a few minutes:
5 If you wish, tap on the Graph menu, select Autoscale Once: and you should see: Do not be alarmed if you see the temperature fluctuating ± 0.1 o C. This is OK. 7. Keep your eye on the time (lower right of screen). At the 3.5 min mark get ready to add the LiCl to the water. Lift the lid up carefully but do not move the temperature probe. 8. At the 4 min mark add the LiCl as quickly as possible to the water in the calorimeter, and then replace the lid. A small amount of the solid may stick to weighing paper, but this is OK. You should see the temperature rise rapidly. You do not need to stop the data collection. LabQuest will stop automatically at the 10 min mark. After 10 minutes you should see:
6 9. Stop the stirrer and remove the temperature probe from the solution. It is vital that you wipe off all traces of solution from the temperature probe. Use a wet paper towel to do this several times over, and then wipe dry. Any traces of salt solution will corrode the temperature probe. The solution should be poured into the appropriate waste container. Make sure the magnetic stirrer bar remains in the calorimeter and does not enter the waster container! Rinse the calorimeter with water a few times and then dry. 10. To determine the initial temperature, T i , use the stylus and tap the screen at the 4 min mark. Record the initial temperature in your lab notebook. (In this figure, T i = 22.5 o C.) 11. To determine the final temperature, T f , we need to use the graphing features that are built into LabQuest. Firstly, use the stylus to highlight the flat portion of the curve. To do this, place the stylus on the screen just to the right of the highest point on the graph, drag all the way to the right then release (this similar to using a mouse to highlight text or a figure on a computer). Then tap the Analyze menu and select Curve Fit, and tap in the box next to Temperature: and you should see:
7 From the Choose Fit menu, select Linear: which will then give you the equation of the straight line for this portion of the graph. (In the figure below, the equation is y = – 0.1153x + 35.303).
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