Question

You purify two colorless solids (2 and 3) by recrystallization. Both have a melting point range of 102-104 °C. You forgot to label your work, so you are not sure which solid is 2 and which is 3. You have a small amount of an authentic sample of pure 2 available in your lab. How can you identify the unknowns?

Answer 1

We know that the melting point of impure or mixture is lower and broadens then pure compound.

Here we have pure sample 2 which has sharp melting point.

Now we add small amount of pure sample 2 in both unknown, then determine the melting point of these mixture.

The mixture which have same melting point as sample 2, indicate the unknown is sample 2

The mixture which have lower and broadens melting point, indicate there are two types of compounds which are sample 2 and sample 3.