2,Purification of Solids by Recrystallization
2.1,Competent Chemist Rating:,How do you recrystallize a Mothball?”
Techniques Checklist,
Solubility tests?
Choosing a good solvent system?
Inducing crystallization?
Filtration?
Pre-Lab Discussion and Required Reading,
Theory of recrystallization, Zubrick Ch,13,LLP Ch,11.2
Digital Lab Techniques Manual,
9,Recrystallization
Equipment,
Test tubes (five 13x100 mm)
Erlenmeyer flasks (2x50-mL,1x125-mL)
Small magnetic stir bar
Funnel
Filter paper
Büchner funnel and filter paper
Magnetic stirring/hot plate
Filter flask (250-mL)
Rubber filter adapter
Large vial with white cap
Test tube rack
Large crystallizing dish
Desiccator
19
WARNING NOTICE,The experiments described in these materials are potentially hazardous and require a high level
ofsafety training,special facilities and equipment,and supervision by appropriate individuals,You bear the sole
responsibility,liability,and risk for the implementation of such safety procedures and measures,MIT shall have no
responsibility,liability,or risk for the content or implementation of any of the material presented,Legal Notices
Goal,
You will be given 2.00 g of impure naphthalene
(mothballs!),Your job is to purify the naphthalene by
recrystallization without losing a significant amount of your
Naphthalene
sample!
1
Experiment Outline,
I,Solubility Tests
Determine an appropriate solvent system for the recrystallization of naphthalene,
For your tests try,water,methanol,acetone,hexane,and toluene,To
understand how to find the appropriate solvent or solvent mixture for
recrystallization,see pages 104–105 in Zubrick,
II,Recrystallization of Naphthalene
Transfer the material to a 50-mL Erlenmeyer flask equipped with a stir bar,Add
about 20 mL of the solvent (determined in Part I) and heat to boiling on a stir/hot
plate,
Remove any insoluble impurities by filtration,and recrystallize your product - see
Two-Solvent Recrystallization Guide,
Collect your crystals on a small Büchner funnel by vacuum filtration,and rinse
with the cold solvent mixture,
Your crystals should be colorless,If some orange or yellow color persists,wash
your material with cold hexane,(Be careful,What is the solubility of naphthalene
in hexane?),
Dry your compound well - see Two-Solvent Recrystallization Guide for tips,
Determine the yield,and obtain a melting point.
Results,
To obtain your "CC Rating" in Purification of Solids by Crystallization,
you must obtain colorless,well dried crystals weighing at least 1.30 g (no traces of
yellow!),The purified material must melt over no more than three degrees with the
lower range beginning no lower than 77 °C and the upper range ending no higher
than 83 °C,This material must also be submitted to the TA for possible weight and
melting point verification,
1
Adapted from Fieser,L,F.; Williamson,K,L,Organic Experiments; 7th ed.; D,C,Heath and Company,
Lexington,MA,1992; p,40,
20
2.1,Competent Chemist Rating:,How do you recrystallize a Mothball?”
Techniques Checklist,
Solubility tests?
Choosing a good solvent system?
Inducing crystallization?
Filtration?
Pre-Lab Discussion and Required Reading,
Theory of recrystallization, Zubrick Ch,13,LLP Ch,11.2
Digital Lab Techniques Manual,
9,Recrystallization
Equipment,
Test tubes (five 13x100 mm)
Erlenmeyer flasks (2x50-mL,1x125-mL)
Small magnetic stir bar
Funnel
Filter paper
Büchner funnel and filter paper
Magnetic stirring/hot plate
Filter flask (250-mL)
Rubber filter adapter
Large vial with white cap
Test tube rack
Large crystallizing dish
Desiccator
19
WARNING NOTICE,The experiments described in these materials are potentially hazardous and require a high level
ofsafety training,special facilities and equipment,and supervision by appropriate individuals,You bear the sole
responsibility,liability,and risk for the implementation of such safety procedures and measures,MIT shall have no
responsibility,liability,or risk for the content or implementation of any of the material presented,Legal Notices
Goal,
You will be given 2.00 g of impure naphthalene
(mothballs!),Your job is to purify the naphthalene by
recrystallization without losing a significant amount of your
Naphthalene
sample!
1
Experiment Outline,
I,Solubility Tests
Determine an appropriate solvent system for the recrystallization of naphthalene,
For your tests try,water,methanol,acetone,hexane,and toluene,To
understand how to find the appropriate solvent or solvent mixture for
recrystallization,see pages 104–105 in Zubrick,
II,Recrystallization of Naphthalene
Transfer the material to a 50-mL Erlenmeyer flask equipped with a stir bar,Add
about 20 mL of the solvent (determined in Part I) and heat to boiling on a stir/hot
plate,
Remove any insoluble impurities by filtration,and recrystallize your product - see
Two-Solvent Recrystallization Guide,
Collect your crystals on a small Büchner funnel by vacuum filtration,and rinse
with the cold solvent mixture,
Your crystals should be colorless,If some orange or yellow color persists,wash
your material with cold hexane,(Be careful,What is the solubility of naphthalene
in hexane?),
Dry your compound well - see Two-Solvent Recrystallization Guide for tips,
Determine the yield,and obtain a melting point.
Results,
To obtain your "CC Rating" in Purification of Solids by Crystallization,
you must obtain colorless,well dried crystals weighing at least 1.30 g (no traces of
yellow!),The purified material must melt over no more than three degrees with the
lower range beginning no lower than 77 °C and the upper range ending no higher
than 83 °C,This material must also be submitted to the TA for possible weight and
melting point verification,
1
Adapted from Fieser,L,F.; Williamson,K,L,Organic Experiments; 7th ed.; D,C,Heath and Company,
Lexington,MA,1992; p,40,
20
