11.3 Hess's Law on Combustion of Magnesium

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Design
Objective: Find the standard molar enthalpy of combustion for magnesium.

Manipulated Variables- volume of HCl, length of magnesium strip, mass of magnesium oxide, Controlled Variable- type of calorimeter (Styrofoam cup)
Responding Variable- change in temperature
Procedure:
1. Cut out 3 pieces of magnesium strips each with lengths of maximum 5 centimeters. 2. Measure and record the lengths of the magnesium.
3. Scrub the magnesium strips with steel wool to clean out impurities. 4. Pour out approximately 310 mL of hydrochloric acid from the stock container. 5. Use a 50mL or 100mL graduated cylinder to measure approximately 50mL of hydrochloric acid. 6. Record the volume of hydrochloric acid.

7. Measure and record the initial temperature of hydrochloric acid. 8. Pour hydrochloric acid into the Styrofoam cup (the calorimeter) and add magnesium in. 9. Close the lid immediately with the thermometer inside the calorimeter. 10. Wait till the temperature is stable and then record it. 11. Repeat steps 5 to 10 for three consecutive and precise trials (ΔrHm value of each trial should be within 10% of each other). 12. For the reaction of magnesium oxide and hydrochloric acid, tare the scale with the Styrofoam cup on it. 13. Add an amount of maximum1 gram of magnesium oxide.

14. Record the mass of magnesium oxide.
15. Repeat steps 5 to 7.
16. Pour the hydrochloric acid from the graduated cylinder into the Styrofoam cup. 17. Repeat steps 9 and 10.

Data Collection
Data Collection for Magnesium and Hydrochloric Acid Reaction Initial and Final Temperature of Three Different Consecutive Trials of Magnesium and Hydrochloric Acid Reactions Trial| Initial Temperature (±0.1°C)| Final Temperature (±0.1°C)| Change in Temperature (±0.2°C)| 1| 22.8| 27.3| 4.5|

2| 22.6| 26.8| 4.2|
3| 22.6| 26.8| 4.2|

Temperature vs. Time of Trial #1 of Magnesium and Hydrochloric Acid Reaction Time (±0.5s*)| Temperature (±0.1°C)|
0.0| 22.4|
10.0| 22.8|
20.0| 23.0|
30.0| 23.1|
40.0| 23.9|
50.0| 25.3|
60.0| 25.9|
70.0| 26.5|
80.0| 26.8|
90.0| 27.0|
100.0| 27.2|
110.0| 27.2|
120.0| 27.3|
130.0| 27.3|
140.0| 27.3|
150.0| 26.5|
160.0| 26.5|
170.0| 26.5|
* The uncertainty derives from reaction time and the fact that we did not stop the timer for a continuous recording of the time. Therefore the actual time of observing the temperature could be different by 0.5 seconds.

Temperature vs. Time of Trial #2 of Magnesium and Hydrochloric Acid Reaction Time (±0.5s*)| Temperature (±0.1°C)|
0.0| 22.6|
10.0| 22.9|
20.0| 22.9|
30.0| 23.4|
40.0| 24.8|
50.0| 25.2|
60.0| 26.1|
70.0| 26.5|
80.0| 26.9|
90.0| 26.9|
100.0| 26.8|
110.0| 26.8|
120.0| 26.8|
130.0| 26.8|
140.0| 26.8|

Temperature vs. Time of Trial #3 of Magnesium and Hydrochloric Acid Reaction Time (±0.5s*)| Temperature (±0.1°C)|
0.0| 22.6|
10.0| 23.0|
20.0| 23.9|
30.0| 24.1|
40.0| 25.0|
50.0| 25.9|
60.0| 26.3|
70.0| 26.6|
80.0| 26.7|
90.0| 26.8|
100.0| 26.8|
110.0| 26.8|
120.0| 26.8|
130.0| 26.8|
140.0| 26.9|
150.0| 26.9|
160.0| 26.9|

Mass and Length of Solid Magnesium Strip and Volume of Aqueous Hydrochloric Acid for Three Different Consecutive Trials Trial| Length of Magnesium Strip (±0.01cm)| Mass of Magnesium (±0.005g)| Volume of Hydrochloric Acid (±0.1mL)| 1| 4.91| 0.04| 50.1|

2| 4.42| 0.04| 50.2|
3| 4.26| 0.04| 50.1|

Qualitative Observations for Magnesium and Hydrochloric Acid Reaction Trial| Before Reaction| During Reaction| After Reaction| 1| Mg is a shiny metallic stripHCl is a clear liquid| Smoke rises from the calorimeter immediately after magnesium is placed inLid felt warm to the touch| Mg is completely goneThe mixture inside the container is completely clear| 2| Same...
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