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Part IIB: Determination of the Heat of Reaction |
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| In part IIB of the experiment, you will measure the molar heat for the reaction:
MgO(s) + 2HCl(aq) ------> MgCl2(aq) + H2O(l) The procedure is very similar to that in part IIA, but be careful to watch for the differences. Again, transfer 50 mL of 1.00 M hydrochloric acid to the clean and dry "coffee cup" calorimeter. Measure and record its initial temperature. In our example the initial temperature is 20.0 oC, as shown at right. |
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| Next measure the mass of a clean test tube and note it somewhere in the margin on your lab handout. The picture to the left is the mass of the clean 13 X 100 test tube. Add enough magnesium oxide to the test tube to increase the mass by about 0.35 grams. The picture on the right is the initial mass of the test tube plus MgO and is recorded on the lab handout. In our example this mass is 8.699 grams. | |||||||||
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About 0.35 grams of MgO in a 13 X 100 test tube looks like this: |
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| Now pour the MgO into the "coffee cup" calorimeter with the HCl solution, and put the lid and thermometer into place. Rotate the calorimeter and stir with the thermometer to keep the reactants well mixed. As before record the highest temperature you see as the final temperature of the reaction. Once again, it will probably take a few minutes to reach the highest temperature. Below is a picture of the highest temperature from our reaction. The final temperature would be recorded here as 29.0 oC, as shown below. Take the difference between the final temperature and the initial temperature, and record this as the temperature change. | |||||||||
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| Since there will be some MgO powder left behind in the test tube after pouring the MgO into the calorimeter, weigh the test tube plus the MgO powder that was left behind on the balance after recording the final temperature. In the picture below is the mass we recorded on our data sheet as the final mass of the test tube plus MgO. Take the difference between the initial and final masses to find the amount of MgO actually poured into the HCl solution in the calorimeter. | |||||||||
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| Rinse the calorimeter and thermometer with distilled water and dry them. Then repeat this procedure to get a second set of results. | |||||||||
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