Experimental Analysis of Alum: Melting Point Determination and Water of Hydration Investigation

Part I. Melting Point Determination of Alum:

1. Pulverize 0.5 g of dry alum using a mortar and pestle.
2. Pack alum in a capillary tube to a depth of 0.5 cm.
3. Secure the tube to the thermometer, ensuring alum is level with the thermometer bulb.
4. Fasten the thermometer to a ring stand using a clamp.
5. Immerse capillary and thermometer in a beaker of water and heat, recording the temperature range.
6. Repeat the process with a new alum sample.

Part II. Determination of Water of Hydration in Alum Crystals:

1. Set up Bunsen burner on a ring stand.
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2. Heat a red-hot crucible with cover over the burner.
3. Cool crucible, find mass, and record.
4. Add 2g alum crystals, weigh, and heat to remove water of hydration.
5. Cool, measure, and record the mass of crucible, cover, and anhydrous alum.
6. Repeat until a constant mass is obtained.

Materials: Part 1:

• Beaker, 150 mL
• Capillary tubes
• Mortar and pestle
• Notched stopper
• Rubber bands
• Thermometer
• Clamp

Part 2:

• Balance
• Crucible and cover
• Crucible tongs
• Ring support
• Triangle, pipe stem
• Wire gauze

Both Parts:

• Gloves
• Apron
• Goggles
• Alum (AlK(SO4)2*12H2O, 2.5g)
• Bunsen burner
• Ring stand

Analysis and Calculations:

Melting Point Data:

• Group 1: 91.2, 91.6
• Group 2: 91.7, 91.4
• Group 3: 94.4, 92.3
• Group 4: 93.3, 92.9
• Group 5: 91.5, 92.0
• Group 6: 97.6, 96.8

Results:

• Mean Melting Point: 93.1°C
• Deviation from Mean: 1.492°C
• Standard Deviation: 2.18746°C
• Q-Test for Group 6: 0.66 (rejecting with 90% confidence)

Water of Hydration Data:

• Mols Alk(SO4)2: Group 6 deviates
• Mols H2O: Group 6 deviates

Results:

• Mean Mole Ratio: 14.032
• Deviation from Mean: 1.0312
• Relative Precision: 1.292
• Q-Test for Group 6: 0.4369 (rejecting with 90% confidence)

Post-Lab Questions:

1. Objects must cool before mass determination to avoid air-induced instability.
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2. Melting point results were accurate, but Water of Hydration had deviations in Group 6.
3. Additional tests include sulfate percentage analysis or freezing/boiling point determination.

Result/Conclusion:

• Melting Point: 91.4°C (compared to literature 92.5°C)
• Water of Hydration: Mole ratio 14.032 (compared to literature 12)
• Percent error (Melting Point): 1.18%
• Percent error (Mole Ratio): 24.46%

Error Analysis:

• Melting point observation precision and accuracy issues.
• Uneven heat distribution due to not stirring during heating.
• Error in alum quantity for trials one and two.
• Extended heating time suggested for water of hydration determination.
• Cooling time constraints may affect mass measurements.

In conclusion, the experiment provided accurate results with some margin of error. Improvements in observation precision and careful handling during heating can enhance the reliability of future experiments.

The melting point determination of alum was conducted by pulverizing 0.5 g of dry alum using a mortar and pestle. The powdered alum was then packed into a capillary tube to a depth of 0.5 cm and secured to a thermometer, ensuring the alum was level with the thermometer bulb. The thermometer was fastened to a ring stand using a clamp, and the capillary tube and thermometer were immersed in a beaker of water and heated, with the temperature range recorded. This process was repeated with a new alum sample.

For Part II, the determination of water of hydration in alum crystals involved setting up a Bunsen burner on a ring stand and heating a red-hot crucible with a cover over the burner. After cooling the crucible, its mass was measured and recorded. 2 g of alum crystals were added to the crucible, and the combined mass was measured before heating to remove water of hydration. The crucible was cooled, and the mass of the crucible, cover, and anhydrous alum was measured and recorded. This process was repeated until a constant mass was obtained.

Materials used for both parts included a beaker (150 mL), capillary tubes, mortar and pestle, notched stopper, rubber bands, thermometer, clamp, balance, crucible and cover, crucible tongs, ring support, triangle (pipe stem), wire gauze, gloves, apron, goggles, alum (AlK(SO4)2*12H2O, 2.5g), Bunsen burner, and ring stand.

The analysis and calculations presented mean melting point data with temperatures recorded for different groups. The mean melting point was calculated as 93.1°C, with a deviation from the mean of 1.492°C and a standard deviation of 2.18746°C. A Q-test for Group 6 indicated a deviation, leading to rejection with 90% confidence.

Water of hydration data included calculations for moles of Alk(SO4)2 and moles of H2O, with a mean mole ratio of 14.032. The deviation from the mean was calculated as 1.0312, and the relative precision was 1.292. The Q-test for Group 6 suggested rejection with 90% confidence.

Post-lab questions highlighted the importance of cooling objects before mass determination to avoid air-induced instability. The melting point results were deemed accurate, but there were deviations in Group 6 for the water of hydration. Additional tests, such as sulfate percentage analysis or freezing/boiling point determination, were suggested.

The final results and conclusion included a melting point of 91.4°C (compared to literature 92.5°C) and a water of hydration mole ratio of 14.032 (compared to literature 12). Percent errors were calculated as 1.18% for melting point and 24.46% for the mole ratio.

Error analysis identified issues such as precision and accuracy in melting point observations, uneven heat distribution due to not stirring during heating, errors in alum quantity for trials one and two, and the suggestion of extended heating time for water of hydration determination. Cooling time constraints were also acknowledged as a factor affecting mass measurements. In conclusion, while the experiment provided accurate results, improvements in observation precision and careful handling during heating were suggested to enhance the reliability of future experiments.