Question

1. How did the melting point of your acetanilide change after recrystallization?

2. Why would you test the purity of your acetanilide by mixing it with a known, pure sample of acetanilide and rechecking the m.p.?

Answer 1

Q1.

Typically, we have a sample with acetanilide and impurities.

Recall that impurities may or may not change the melting point (MP) depending on their characteristics.

If they are non-soluble, they will not affect it. It they are soluble, they will affect, typically reducing it.

Now... we use crystallization in order to

- get rid of impurities

- increase the lattice / crystal shape of the acetanilide.

Then, most impurities are gone.

The MP will not be depressed, therefore, expect a HIGHER value of MP fo rthe pure recrystallized sample of Acetanilide.

Q2.

We would want to do this in order to compare the values of pure/impure MP as a reference.

The pure sample of an acetanilide should mark the "range" of temperature in which we should see/observe the change in color, and phase transition.

This helps so we can know the expected range, for instance, insted of waiting 1° per test, we can go directly to the desired range