Calorimetry and Hess' Law

Only available on StudyMode
  • Download(s) : 285
  • Published : November 14, 2008
Open Document
Text Preview
Experiment 11
Calorimetry and Hess’s Law

Purpose- To determine the change in enthalpy for four reactions using calorimetry and Hess’s Law

Procedures:

A.Calibration of the Calorimeter
1.Obtain two copper cylinders and a Styrofoam cup with lid from your lab instructor. Check out a digital thermometer display from the storeroom window. 2.Set up a hot water bath using a 600mL beaker, ring stand, and Bunsen burner. Weigh the two copper cylinders to the nearest 0.01 grams. Carefully place the two copper cylinders in a 25mL test tube. Place the test tube in the hot water bath, and let the bath come to a boil while proceeding with the next step. 3.Weight the clean, dry Styrofoam cup to the nearest 0.01 g. Add 60 mL of distilled water to the cup, and reweigh the cup and water to the nearest 0.01 g. Place the cup in 400mL beaker for stability. 4.Using the digital thermometer record the temperature of the water in the cup every 30s for 4 minutes. Keep the lid on the cup, and keep the cup away from the hot water bath. 5.After the water has boiled for at least 10 minutes, record the temperature of the hot water bath using -20C to 100C thermometer. Carefully remove the test tube containing the copper cylinders from the hot water bath. Quickly dry off the test tube, and dump the copper cylinders into the Styrofoam cup. Replace the lid and immediately record the temperature with the thermometer. 6.Continue to record the temperature every 30s for at least 5 minutes. Whenever the readings are being taken, occasionally swirl the water in the cup to assure uniform temperature. Stop taking readings when a constant decrease in temperature is noted for 4consecutive readings. 7.Dump out the water and return the copper cylinders to your lab instructor now. B.Measurements of H for neutralization reaction.

8.Add 50mL of distilled water to the cup, and pipet 10mL of standardized 3.0M HCL into the water in the cup. Record the exact molarity of the HCL solution given on the bottle. Weigh the cup and HCL/H2O solution to the nearest 0.01 g. 9.Obtain about 20mL of 3.0M NaOH solution. Record the exact molarity of the NaOH solution given on the bottle. Record the temperature, T0, of the solution using the digital thermometer and use a small amount to rinse the pipet. 10. Rinse the probe with distilled water, dry it and use the digital thermometer to record the temperature of the solution in the cup every 30s for 4 minutes. Occasionally swirl the cup. Keep the lid on the cup. 11. Pipet 10mL of the standardized NaOH solution into the HCl solution in the cup. Swirl the cup to mix the contents. Replace the lid and immediately record the temperature with digital thermometer. 12. Continue to record the temperature every 30s for at least 5 minutes. Stop taking readings when a constant decrease in temperature is noted for 4 consecutive readings. 13.Dump out the solution and rinse out with distilled water. C.Measurement of Hf for Mg2+ (aq).

14.Weigh out 0.12g of magnesium turnings to 0.0001g on the analytical balance. 15.Add 40mL of distilled water and 20mL of 6M HCl to the cup. Weight the cup and HCl solution to the nearest 0.01g. Swirl the cup to mix the contents. 16.Using the digital thermometer, record the temperature of the solution every 30s for 4 minutes. Occasionally swirl the cup. Keep the lid on the cup. 17.Carefully add the magnesium turnings to the HCl solution in the cup. Swirl the contents in the cup. Replace the lid and immediately record the temperature with the digital thermometer. 18.Continue to record the temperature every 30s for at least 5 minutes. Stop taking readings when a constant decrease in temperature is noted for 4 consecutive readings. 19.Dump out the solution and rinse the cup with distilled water. Return the cup and lid to your instructor, and the digital thermometer to the storeroom window. D.Determination of H for two other reactions using Hess’s...
tracking img