Organic Chemistry Laboratory I - Chem 341

Quiz 2c

1. Define the term “flash point” as it pertains to organic solvents. (1 pt)

The flash point is the temperature at which an organic compound can spontaneously ignite. For many solvents this is very low, for instance the f.p. for diethyl ether is –40C.

2. Draw the chemical structure of 2-naphthol. (1 Pt)

3. Explain the process of “seeding” as it pertains to a recrystallization? (1 pt)

The process of seeding is used to induce crystal growth when crystallization does not occur upon cooling to room temperature. To seed a solution, you take a pure crystal and add it to your solution. This provides a surface for additional crystals to grow from. Other techniques used to induce crystallization include cooling, scratching the flask with a glass rod, and evaporating more solvent to make the solution more concentrated.

4. Circle the compounds that are likely to be soluble in water. (2 pts)

5. What is the reason for performing a hot filtration? (1 pt)

A hot filtration is performed to remove materials that are insoluble, such as sand, dirt, or activated carbon. If the filtration were performed at room temperature, then the desired compound would crystallize out on the cold filter paper and funnel. By ensuring that it is hot, most of the desired compound will remain dissolved and pass through the filter paper.

6. During a recrystallization, why is it important to allow the solution to slowly cool to room temperature rather than rapid cooling with an ice bath? (2 pts)

Rapid cooling tends to trap impurities within the crystal lattice. Slow cooling allows the desired molecules to organize into a well-defined crystal and leave the impurities in solution.

7. Why is anhydrous sodium sulfate added to the organic phase after the last extraction? (2 pts)

Anhydrous sodium sulfate absorbs any water that may remain in the organic solvent after the extraction. This residual water often causes the organic phase to look cloudy; the solution generally clears up after addition of the sodium sulfate drying agent. The sodium sulfate is then removed by filtration prior to evaporation of the solvent.