1. A hot solution of a particular compound was allowed to cool to room temperature. After...

1. A hot solution of a particular compound was allowed to cool to room temperature. After waiting a few minutes, it was noticed that the crystallization had not taken place. Discuss two ways to induce crystallization.

2. What properties are necessary and desirable for a solvent in order that it is well suited for recrystallizing a particular organic compound?

3. Assume that 3.0 g of aniline and 4.5 ml of acetic anhydride are used in the preparation of acetanilide. What is the limiting reagent? What is the theoretical yield of acetanilide? What is? the percentage yields if 3.3 g of acetanilide is obtained?

4. The solubility of compound A in ethanol is 0.4 g per 100 ml at 0o C and 5.0 g per 100 ml at 75 o C. What is the minimum amount of solvent needed to recrystallize an 8.0 g sample of compound A? How much would be lost in the recrystallization?

5. Impure acetanilide was dissolved in hot water. The solution was filtered hot and the beaker of solution was immediately placed in an ice-water bath instead being allowed to cool slowly. What will be the result of cooling the solution in this manner?

Expert Solution

One way to induce crystallization is solvent evaporation. In this technique, a saturated solution is prepared in a suitable solvent. This sample is left in a vial that has a perforated cap. The perforation may depend on the volatility of the solvent used. The vial is kept aside until all the solvent is evaporated. Once, the solvent starts evaporating, crystals grow in the vial and they can be collected after complete evaporation. This method best suits for air stable samples.

Another method to induce crystallization is vaccum sublimation. In this method, a small amount of sample is sealed under vaccum and is subjected to a temperature gradient on a warm oven. This temperature is sufficient to produce crystals within a span of time depending on the volatility of the sample and the quality of the vaccum. This method is very ideal for air sensitive compounds and a large number of compounds can be sublimed to form excellent crystals.

queen_honey_blossom answered 1 year ago

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