Pre Lab Experiment 3: Recrystallization

Question 1

Why is it hard to master “intuition” in recrystallization?

Answer 1

Because if you do a step too fast than you will get impurities rather than selective crystal growth

Question 2

How do select a good solvent?

Answer 2

1) Solubility (not soluble at room temp, but readily dissolves at boiling temp)
- Like dissolves Like
- Impurities dissolve very well OR not at all
2) Not chemically reactive
3) B.P. of solvent is less than M.P of the solid to prevent oiling out

Question 3

What are the two compounds you will be using in Recrystallization lab?

Answer 3

Benzoic Acid and Acetanilide

Question 4

What solvent will we be using for this lab? Why?

Answer 4

We are recrystallizing with water because these 2 compounds are polar.

Question 5

Which compound is contaminated with insoluble sand, and coloured soluble impurities? How do we remove these impurities? What precautionary steps do we need to take?

Answer 5

Acetanilide is contaminated. We must add:
1) Norit -to remove coloured, soluble impurities
2) Celite -to absorb Norit and attached impurities
3) New boiling chip -to prevent bumping (violent frothing)
4) Excess solvent - to prevent premature of solvent onto the receiver or funnel
SAFETY: Solution can’t be hot when addicting Norit or boiling chip!