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Introductory Sequence: Recrystallization

Page history last edited by jbfriesen 9 years, 7 months ago

03_Solubility2012_class_data.xlsx Summary of Procedure:

The solubility of 5 known compounds is studied in three different solvents at four different temperatures.

The information on solubility is used to recrystallize the two unknown compounds from the previous labs.

Similar to the TLC experiment, the students work in groups to gather data for the first part.

2010 Student Handout: Recrystallization

2008 Student Handout: Recrystallization

Positive aspects of this experiment:

+ Recrystallization is a fundamental Organic Chemistry technique. This experiment allows students to practice this technique. Filtration of a precipitate is another common technique in Organic Chemistry.

+ The improvement to the solids by recrystallization is often readily evident.

Neutral (may be positive or negative) aspects of this experiment:

± Heptane is preferred to hexane because it won’t boil away in the hot water bath.

Negative aspects of this experiment:

- Judging the qualitative “solubility” of a compound is difficult. Students tend to get variable results from this part.

- Recrystallization is difficult to do without significant loss of compound. What looks like a large quantity of fluffy crystals may turn out to be “nothing.”

Inquiry & Extension Ideas:

● Solubility characteristics can be quantified. This allows a statistical analysis of the class results.

● Is there a link between TLC “polarity” and solubility?

● The “Green” question about the relative environmental friendliness of the three solvents is very interesting.

Data Links:

2012 Solubility Data