1.List some advantages as well as disadvantages to using the Craig tube crystall
ID: 1000988 • Letter: 1
Question
1.List some advantages as well as disadvantages to using the Craig tube crystallization technique.
2.What was the purpose of using activated charcoal in this experiment? Did you notice any differences before and after the addition of the activated charcoal?
3.Describe the purpose of each of the following as they apply to recrystallization.
Seed crystals
Boiling stones
Celite
4.Why must the acetanilide be completely dry before obtaining its melting point?
5.Why does slow, controlled cooling generally give better crystals than rapid cooling?
6.How do you know if you happen to use too much recrystallization solvent? If you encounter this problem, what can you do?
7.Why do you think a stemless funnel was used rather than a long stem funnel during the gravity filtration step?
8.How do the melting points of the impure acetanilide and the recrystallized acetanilide compare?
Explanation / Answer
1.List some advantages as well as disadvantages to using the Craig tube crystallization technique. ADVANTAGE • If you are working with a relatively small amount of material (10-100 mg) is easier and provides a better product recovery percentage • Requires less energy for separation distillation or other methods commonly used and can be performed at relatively low temperatures. DISADVANTAGES • Not applicable to large amounts. • The operation involves the handling of solids, with technological drawbacks that this entails. In practice is a solid processing sequence, including crystallization equipment together with other solid-liquid separation and drying. 2.What was the purpose of using activated charcoal in this experiment? Did you notice any differences before and after the addition of the activated charcoal? When the solute contains colored or resinous impurities , it is customary to add a selective adsorbent such as activated carbon to remove . Usually appear when the mixture in case of using activated carbon, has to remove the ball of fire, and place a minimum amount of activated carbon is heated , because if you add being in the fire can produce extremely dangerous projections . Then it is filtered hot to remove it. 3.Describe the purpose of each of the following as they apply to recrystallization. Seed crystals: The placement of a seed crystal into solution allows the recrystallization process to expedite by eliminating the need for random molecular collision / interaction Boiling stones: It is used to control the boiling point of the solution Celite: If the activated solution is added charcoal boiling. Once the coal is suspended in the solution add a small amount of Celite (150-200 mg). Celite is a common filtration adjuvant used in organic chemistry. Its addition will help prevent any carbon particles from escaping through the filter paper 4.Why must the acetanilide be completely dry before obtaining its melting point? For greater accuracy acetanilide must be passed by the stove, to thereby remove the water that is in the acetanilide . And if the melting point is obtained when the acetanilide not dry not have a good accuracy, since the mixtures have a melting point lower than that of the pure substance. That is that alters the structure that holds the molecules, which makes it a solid. 5.Why does slow, controlled cooling generally give better crystals than rapid cooling? The crystallization process is a balance between the molecules in solution and which are incorporated into crystals. Since the crystal structure is highly ordered, different molecules, such as impurities, not included in the crystal structure and re- dissolution. Therefore only required compound molecules are retained on the surface of the crystal lattice and impurities remaining in the mother liquor. For successful crystallization, the cooling must take place slowly so that crystals can form slowly and can operate the balance excluding the impurity molecules from the crystal lattice. If the solution is cooled too fast, impurity molecules or be trapped included in the crystal lattice. 6.How do you know if you happen to use too much recrystallization solvent? If you encounter this problem, what can you do? The amount of solvent is important , since the amount of crystals determined to be formed . Having too much solvent will be more difficult to reach the recrystallization as they remain more dissolved time and what we want is that we are not dissolved , but the main reason is because the main point of making a recrystallization is " purify" a substance with high performance , ie the amount of solute is put almost similar to the pure you get solute or solvent recrystallized and much would occur lost. 7.Why do you think a stemless funnel was used rather than a long stem funnel during the gravity filtration step? A funnel stemless to thereby prevent clogging of the stem with crystals is used. 8.How do the melting points of the impure acetanilide and the recrystallized acetanilide compare? The purity of the crystallized compound is tested through its melting point. This intrinsic physical property to each compound serves as an indicator for determining the purity of the solids obtained. The melting point of any crystalline solid is the temperature at which it passes from the solid phase to the liquid. The value of the melting point is fixed for pure substance, however, impurities having this value changes. Therefore the melting point deviation of acetanilide depend on the crystallization yield.
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