Question

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Recrystallization of Acetanilide Recrystallization is an important method used by chemists to purify solid compounds. When a chemist conducts a chemical reaction as shown in Scheme 1, it will rarely go to 100% completion, and will frequently produce byproducts. These byproducts and some of the unreacted starting materials will be present in the end as impurities. Chemists need ways to remove these unwanted impurities so they can isolate their desired product in its pure form. ΝΗ. OCH HOCH Aniline Acetic Anhydride Acetic Acid Acetanilide Scheme 1- Synthesis of Acetanilide Recrystallization takes advantage of the fact that a given compound's solubility increases with temperature. If a crystalline compound is fairly insoluble in cold solvent, the solvent could be heated, causing it to dissolve. If this hot solution is then cooled, the compound will gradually become insoluble and will recrystallize. Crystals that have been recrystallized tend to have fewer impurities trapped in them. There are generally two reasons why impurities are excluded during recrystallization. First, impurities usually have a different solubility and will either not dissolve in the boiling solvent and be filtered out, or they may stay dissolved in the cold solvent during recrystallization. Second, they are excluded from the crystal growth because crystals often form by ordered packing as shown below (Figure 1A), making a highly stable crystal structure. Crystals that incorporate an impurity while forming will be less stable and are, consequently, less likely to form (Figure 1B). AD Figure 1- Crystal Structures: Contrast between a pure crystal "A" and an impure crystal "B" with trapped impurities.

Answer 1

1) Yes recrystallization increases the purity of the solvvent. Because of the crystal growth.

2) The maximum amount cannot be calculated but it can be said that after the purity will be much more than 90%.

3) Slow cooling gives the better crystal.

4) Filteration.

6) It generraly increases the melting point as the compoubd after recrystallization the compund is held tightly in lattice.

7) Minimal amount of solvent is needed because the solvent also have to evaporate which will take less time

8) Cheking the melting point with the literature value. Getting NMR and Mass spectra