Experiment 3: Purification Techniques

What is the total amount of crystallized A expected after the recrystallization process?

Which solvent can be used for the recrystallization of the unknown compound according to the procedure?

What is the maximum solubility of Acetanilide in cold water as provided in the data?

What should be done with the solid waste after the experiment?

Why is it necessary to use boiling chips or a stir bar when boiling water?

What is the primary purpose of recrystallization in the laboratory?

How does temperature affect the solubility of compounds during recrystallization?

What occurs to impurities in a mixture during the recrystallization process?

What observation would indicate a compound is pure after recrystallization?

Given the solubilities in boiling solvent for Compound A (4.0 g/100 mL) and Compound B (6.0 g/100 mL), how much boiling solvent is required to dissolve 2.0g of Compound A?

If 50 mL of boiling solvent is added to a mixture containing 2.0g of A and 0.3g of B, how much of Compound B could dissolve in that volume?

What is the appropriate method to recover the crystallized solid after cooling the solution during recrystallization?

Which factor is NOT typically associated with broad melting point ranges in solids?

Experiment 3: Purification and Identification of an Unknown Solid

Key Lab Skills and Techniques: Recrystallization and measuring melting points
Key Concepts:
- Recrystallization: Based on the difference in solubility of a solid in hot vs cold solvent.
  - Dissolving the solid in a minimal amount of boiling hot solvent.
  - Cooling the solution, leading to crystallization of the dissolved solid as solubility decreases.
  - Impurities are removed through filtration, either dissolved in the cold solvent or removed from the hot solvent.
  - Pure solids have a sharp melting point range (usually 2 degrees or less).
- Melting Point: A characteristic property of pure substances.
  - Broad melting point ranges indicate impure compounds.

Recrystallization Procedure

Procedure: Recrystallize the unknown solid from last week using water.
- Important: Carefully read the section on recrystallization in "Organic Chemistry Lab Techniques" by Nichols.
Procedure: Measure the melting point of:
- The purified unknown.
- The unknown mixed with acetanilide.
- The unknown mixed with phenacetin.

Recrystallization Example with Compounds A & B

Solubility: Compound A and B have different solubility in hot and cold water.
- Example: 2.0 g of Compound A and 0.3 g of Compound B in a mixture.
  - 50mL of boiling water is required to dissolve all of Compound A.
  - 3.0g of Compound B could dissolve in 50 mL of boiling water.
  - After cooling, 0.15 g of Compound A and 0.4 g of Compound B remain soluble in the cold solvent.
  - Crystallization: 1.85 g of Compound A crystallizes out of the solution (2.0 g - 0.15 g = 1.85 g).

Chemical Used

Acetanilide and Phenacetin: Two compounds used in the experiment.
- Both have different solubility in hot and cold water.

Safety Considerations

Hot Surfaces: Exercise caution to avoid burns.
Boiling Water: Use boiling chips or a stir bar to prevent bumping.

Results

Results: Record:
- Mass of the unknown before and after recrystallization
- % purity of the unknown from last week
- Melting point of the pure unknown
- Melting points of the mixtures (unknown with acetanilide and unknown with phenacetin)

Waste Disposal

Acetanilide and/or Phenacetin: Solid waste container.
Filtrate: Aqueous waste container.
Acetone: Organic waste container.

This quiz focuses on the key lab skills and techniques for the purification and identification of an unknown solid through recrystallization and melting point measurement. You will explore the differences in solubility and the importance of sharp melting point ranges in determining purity.