2.1: Experiment 9 Practical Tips
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1. Do not use “filter tip” pipettes. Just follow the procedure given in recitation (see attached flow chart) to get rid of solids.
2. To prepare the column shown on p. 73 of the textbook, use a Pasteur pipette with a minimum amount of cotton (just enough to hold the solid alumina in place).
3. Do not pack the cotton plug used in step 2 too tight. If you have too much cotton or if it’s packed too tight the filtration process will take a long time.
4. In order to evaporate the solvent in the warm water bath, place the methanol solution in a small beaker, not in a heavy wall vial. If you use a heavy wall vial it will take much longer to evaporate the solvent because the vial takes longer to heat and is too tall (vapors take longer to escape out of the vial).
5. There is no need to evaporate all the solvent (methanol) completely. As soon as about 80% or more of the solvent has evaporated, you can go to the next step. If you don’t see any solid, all you have to is let the solution cool to room temperature and a solid will appear.
6. If a solid does not appear even at room temperature, place the beaker in ice bath for about 5-8 min. a solid should appear. Then you’re ready for the filtration.
7. During the vacuum filtration do not open the water faucet full blast, just enough to create the suction needed for the filtration.
8. When you open the water faucet make sure the hoses attached to it drain the water into the trough and do not splatter out to the counters.
9. Have one member of each group learn how to use the melting point instrument while the others continue with the experiment. This will prevent a time crunch at the end with everyone trying to take a melting point while also trying to learn how the instrument.
10. Have fun!