Recrystallization & Melting Point: Identifying a Component of “panacetin”

Recrystallization & Melting point:

Identifying a component of “Panacetin”

Pre-Lab Questions:

1. Determine if the following statements are true or false.

1. A mixture will have a lower melting point than the melting points of either of the pure substances that are in the mixture.

True

1. You should never heat a mineral oil bath above 300 of a substance

True  

1. Only pure substances have sharp melting points (narrow melting point ranges)

True

1. At what rate should the temperature of the melting point apparatus rise when taking the final melting point of an unknown substances?

The temperature of the melting point apparatus should rise when taking the final melting point of an unknown substances at a narrow range (1–2°C or less) at a temperature close to the literature value, it is probably quite pure. In the other hand if its melting-point range is broad and substantially lower than the literature value, it is probably.

1. During recrystallization, the solution is slowly cooled after hot gravity filtration, allowing the solute to crystallize out. What is wrong with crystal sizes at the two extremes listed below?

1. Very small crystals

Small crystals have a large surface area to volume ratio and impurities are located on the surface of the crystals as well as trapped inside the matrix.

1. Very large crystals

Slow crystallization gives larger crystals than fast crystallization. It’s contaminated and has impurities  

1. List two methods you might use to induce crystallization in a solution where the solid does not want to crystallize out.

You might induce crystallization in a solution by scratching the sides of the container with a glass stirring rod. The tiny scratch provides a rough surface on which the crystallization may begin. Then cool the container further in a beaker containing ice and tap water to increase the yield of product. The same result could be obtained by adding a small “seed” crystal of that substance, assuming a small amount of solid had been saved.