Overview and Instructions for the Lab Report
Recrystallization is a common method to purify a solid product in a reaction which contains impurities from the filtration process used to isolate it. When a product is collected and dried, a melting point range is taken to identify the solid, and also gives information about its purity [See Lab #4 – Melting Point]. Ann impure solid can be recrystallized to remove impurities, provided the correct solvent is chosen for that process.
Note: Review the material posted on Moodle for the procedure. An additional step may be the following:
If a solid seems discolored from the impurities, then decolorizing (absorbent) carbon is added along with the hot solvent to remove those specifically colored impurities. It does not interfere with the recrystallization because it is present in very small amounts.
Lab Report – Instructions
Your report will consist of an analysis of the results presented here. Answer the questions below.
The data and other information for the recrystallization of an impure sample of acetanilide is provided in the table.
Mass of impure acetanilide
Mass of acetanilide after recrystallization
Mass of watch glass and recrystallized acetanilide
Mass of watch glass
Volume of water added
Melting point range of impure solid
116 – 121 oC
Melting point range of recrystallized solid
120 -122 oC
1.) Determine the value for the missing entry in the data table and then calculate the % recovery after recrystallization. Show this calculation.
2.) Interpret the melting point range values for purity in comparing the impure and the recrystallized solid. Is the result more pure? How did you conclude that?
ANSWER THESE WITH COMPLETE SENTENCES. You will have to review the material on Moodle about the method for this information.
1.) What is the most important criterion of solubility in making the choice for a specific solvent? Hint: It has to do with temperature.
2.) What would you expect if you did a second recrystallization? (This is commonly done.)