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Lecture 6

CHEM 235 Lecture Notes - Lecture 6: Ground Glass Joint, Boiling Chip, Petroleum Ether

Course Code
CHEM 235
Dana Zendrowski

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LAB 6 (PART 2)
1. Take a small test tube and put 3 drops of solvent, add few crystals, look if dissolved, agitate
2. Put the test tube in boiling water bath for a min (petroleum ether -> warm tap water) , watch
for dissolving, if not add few more drops (not more than 20)
3. 2 minutes of boiling, observe if dissolving
4. Figure out the solvent pair for one/both compound
5. Scrape out solid from RB flask, transfer it to 50 ml Erlenmeyer flask with ground glass joint
6. Start recrystallizing in RB flask with small amount of solvent , add boiling chip
7. Add west condenser on the RB, place it on THERMOWELL , clamp the west condenser. Water in
bottom, water out- top
8. Heat the mixer and swirl the flask, once dissolved transfer solution from RB to EF quickly
9. Add solvent to dissolve compound in EF.
10. Add cork size 7, clamp the flask at 45 deg on the vertical poles
11. Wait 30 min for crystal to form (otherwise crystals forms in 5 min, add more solvent and reheat)
12. Suction filtration:
- Need suction trap, 125 ml filter flask, filter vac, Buchner funnel, small filter paper, glass rod
with rubber tip, spatula, watch glass, solution
- Use 3 pronged clamp to attach the suction flask with the vertical rod
- Attach tube from suction trap to suction flask
- Add filter vac, Buchner funnel and a filter paper on the suction flask
- Wet filter paper with a bit of cold solvent
- Attach the tube to the aspirator and turn on full
- Unmount the tube before pouring the solution in s.f, use the glass rod to hold still the filter
- Reattach the tube, press down filter vac, use rubber tip to scrape out solvent or use the
mother liquor to rinse it out
- Use the suction to air dry the crystal for few mins
13. Use the spatula to take out the filter paper with crystals on the watch glass, let it dry and cover
Solvent-pair Recrystallization:
1. (AFTER STEP 8) dissolve the solvent in minimum amount of boiling solvent (5 10 ml) which is
very soluble
2. Solution is boiled and all the compound is dissolved. Slowly add second solvent from the top of
west condenser.
3. Stop adding when cloudiness appears, and don’t disappear with swirling and heating
4. Add enough of the first solvent to clear the cloudiness (CONTINUE TO STEP 10)
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