1. Suppose you dissolve a compound in too much solven in a recrystallization. Ho
ID: 820187 • Letter: 1
Question
1. Suppose you dissolve a compound in too much solven in a recrystallization. How would you find out that you had used too much solvent? Given that too much solvent has been used, what can you do about it?
2. Suppose a Craig tube assembly has been chilled in an ice bath. Why must the "filtration" step be performed quickly?
3. Acetanilide has a mp of 114 degrees C, yet it apparently melts in boiling water. Explain.
4. Why is it necessary to dry the purifiied acetanilide before taking a melting point?
5. Explain why slow cooling tends to give "better" crystals in a recrystallization than the crystals obtained upon rapid cooling.
6. A compound is soluble in ether at room temp. but not very soluble at -80 degrees C ("Dry Ice" temp). Would ether be a useful crystallization solvent for the compound? Explain.
Explanation / Answer
1. No crystallization will occur because the solution is to dilute. If there is to much solvent then you would either need to boil the excess water in this case or solvent off, or begin again.
2. it is placed in a water bah quickly so that is can begin to crystalize at the bottom of the craig tube.
3. There is a depression in the melting point of impure samples and it is misable in water so becasue both are polar it can seemingly dissolve in water.
4. there still can be solute particles in the non dry compound so it will not give you an accurate amont of yeild of the product thus increasing the melting point
5. When the solution is cooled slowly it is more uniform and gives a more accurate result as opposed to quick cooling that is not as uniform.
6.the ether would not make a good solvent although it is polar and the dry ice in non polar becasue it is too good meaning that you wouldnt recover much of the compound.
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