Acquire approximately 1.00 g of one unknown “crude” solid. Place sample in 125-mL Erlenmeyer flask. | - Unknown D acquired.
- White/orange-ish color, flaky
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Find a rough melting point of the sample using a Mel-Temp Apparatus and melting point tube, recording range (1st recording when sample begins to melt and final recording when sample is completely melted). Use this range to make a hypothesis about what the unknown is. | - Sample tamped into mp tube easily
- Start mel-temp below lowest known mp, kept close watch until melting occured
- Range: 122.4-123.6°C
- Clear transition, all melted completely, still an orange color
- Hypothesis for unknown: Benzoic Acid (given range: 122-123°C)
- Mel-Temp apparatus set up as below:
[pic 1] |
Determine a good solvent for recrystallization (0.10g solid + 3mL of solvent). Heat (no flames), cool, and ice-water bath to see crystals. If no solvent works may have to use mixed-solvent. | - 3 possible solvents listed in class:
- Boiling Water: no dissolving
- Room Temp Water: No Dissolving
- Methanol: All Dissolved (left orange at the bottom of test tube)
- Mixed solution necessary: Methanol + Water
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After selecting appropriate solvent, heat solvent and add to solid in Erlenmeyer flask. Filter any impurities through gravity filtration. Activated Charcoal may be used to filter out any discoloration that should NOT be present. | - 1.00 gissolved with approx. 10mL of Methanol (all dissolved with impurity left at bottom)
- Gravity Filtered with Setup below:
[pic 2] - No Activated charcoal needed
- All impurity (sand) left in filter paper
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Allow flask (with dissolved solid and solvent) to cool and put in ice bath to allow for crystallization. Agitate with glass rod if no crystals form. | - Since mixed solution, used water to allow for recrystallization
- No recrystallization after addition of water, stirring, or agitating with glass rod
- Used hot plate to boil off excess Methanol
- Added water -> crystal formation
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Filter crystals with Buchner funnel and vacuum. Use Water trap with Water Aspirator (water all the way on). | - Buchner funnel and vacuum apparatus set up as below:[pic 3]
- Small amount of water used to get remaining crystals from flask into Buchner funnel
- Vacuum hook ups available in lab, no water aspirator necessary
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Allow crystals to dry and take weight. | - Used larger filter paper to dry crystals
- Left on vacuum for excess time to pull unwanted water out
- Final weight: 0.233g
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Find the melting point (RANGE) for the pure sample. | - Mel-Temp apparatus set up as last time, closer to known range and slower rate of temperature increase
- Range: 121.6-122.6°C (given range: 122-123°C)
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The above steps should be repeated for the microscale unknown. With the exception of using a smaller amount and a Hirsch funnel instead of a Buchner funnel. | - Unknown Q acquired (approx. 0.1g)
- Flaky, bright yellow
- Crude melting point from mel-temp apparatus: 130.0-131.8°C
- Smooth transition to melt
- Stayed completely yellow upon melting
- Hypothesized unknown: trans-9-(2-phenylethynyl)-anthracene (given range: 131-132°C)
- 0.0993 g unknown Q added to 100 ml Erlenmeyer flask
- Recrystallization solvent given in lab: isopropanol
- Isopropanol at room temp. = no dissolving
- Heated isopropanol = dissolved unknown completely
- Just enough solvent needed to completely dissolve the 0.0993g of solid in Erlenmeyer flask used (approx. 2mL)
- Flask added to boiling water to dissolve all crystals
- Gravity filtration not needed b/c pure unknown
- Flask allowed to cool to room temperature before added to ice bath to allow for complete recrystallization
- Vacuum filtered through Hirsch funnel (apparatus looks similar to before, just on smaller scale).
- Sample allowed to dry
- Final weight: 0.0930g
- Final melting point range: 130.7-131.4°C (given range: 131-132°C)
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For the liquid unknown, the boiling point is found by using the microscale method (Siwoloboff’s method). Repeat 3 times. Use boiling point ranges found to determine the unknown’s identity. | - Unknown Liquid B acquired
- Clear liquid
- Micro boiling point apparatus set up as below:
[pic 4] - All air allowed to escape capillary tube, once bubbles transitioned from slow (air release) to rapid (boiling) entire apparatus removed from heat
- First measurement in range (high end) measured when liquid unknown started to fill capillary tube.
- Second measurement in range (low end) taken when liquid quit filling capillary tube
- First measurement (only recoded when capillary tube filled—missed initial reading): approx. 65°C
- Second: approx. 67-65°C
- Third: approx. 69-67°C
- Unknown identity determined to be Tetrahydrofuran (pre-researched bp found to be approx. 65°C)
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Use another Physical property to determine identity of unknown. | - For the sake of this lab, an additional physical property was not needed to be found, instead boiling point range was found 3 times to insure accuracy.
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