B. Determination of the Enthalpy of Formation of Magnesium Oxide...

B. Determination of the Enthalpy of Formation of Magnesium Oxide

Magnesium Reaction
1. Ensure that the calorimeter vial used in Part A is clean and dry.
2. Assemble the calorimeter as shown in Figure B2.2. Pour the entire contents of the bottle of pre-measured 20 mL of hydrochloric acid (1 mol ⋅ L−1) into the vial. Ensure that the thermometer bulb is below the surface of the liquid, and determine the temperature of the hydrochloric acid.
3. Pour the entire contents of one of the pre-weighed vials of magnesium powder (approximately 0.12 g) into the hydrochloric acid contained in the calorimeter. Stir the mixture vigorously, taking care not to hit the thermometer with the stirrer. Read the temperature of the reaction mixture every 15 seconds, until it reaches a maximum. Thereafter, read the temperature every minute for five minutes.
4. Check the contents of the calorimeter. If all the magnesium did not dissolve, you must start Part B again.
5. Dispose of the contents of the calorimeter vial down the drain with plenty of water. Wash the vial with water, and dry it with tissues or paper towels.
6. Repeat steps 1 though 5 for a second determination.

Magnesium Oxide Reaction
1. Set up the calorimeter as before. Again pour the entire contents of the bottle of pre-measured 20 mL of hydrochloric acid (1 mol ⋅ L−1) into the calorimeter vial, and measure the temperature of the acid.
2. Pour the entire contents of one of the pre-weighed vials of magnesium oxide (approximately 0.25 g) into the hydrochloric acid contained in the calorimeter, stir thoroughly, and monitor the temperature change in exactly the same manner as you did in step 3, above.
3. Check the contents of the calorimeter.
If you can see any unreacted magnesium oxide you must repeat the experiment.
4. Dispose of the contents of the calorimeter down the drain. Wash the cup with water, and dry it with paper towels or tissues.
5. Repeat steps 1 through 4 for a second determination.