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JoVE Lab Manual
Lab: Chemistry

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Learning Objectives

At the end of this lab, students should know...

What is recrystallization used for?

Recrystallization is a method to purify solid compounds based on the differences in solubility in a solvent.

What are the steps of recrystallization?

1-Choosing the solvent or solvent pairs, 2-dissolving the sample in the minimum volume of the hot solvent, 3-cooling the saturated solution, 4-collecting and washing the crystals, and 5-drying.

What is an ideal solvent with respect to the solute?

An ideal solvent has the following characteristics: it completely dissolves the solute only at high temperatures (near the boiling point of the solvent); it does not react with the solute; it has approximately the same polarity as the solute; it precipitates the solute at low temperatures (near room temperature or lower); and it only dissolves impurities at low temperatures.

When is a solvent-pair used in recrystallization?

A solvent-pair is used when a single solvent with ideal properties cannot be found.

What are the two phases of crystallization?

The two phases of crystallization are nucleation and crystal growth. During nucleation, solute molecules come together to form small stable crystals called nuclei. Then, additional crystal growth occurs on the nuclei, increasing the size of the crystals. This is because solute molecules have a higher affinity for joining existing solute crystals than forming new crystals.

List of Materials

  • Lab stand
  • 3-prong clamp
  • Stirring hotplate
  • Flask tongs
  • Vacuum pump or house vacuum wih tubing
  • 125- or 250-mL glass filter flask
  • Büchner funnel
  • Filter adapter
  • 600-mL glass beaker
  • 250-mL glass beaker
  • 5- or 10-mL glass graduated cylinder
  • 10-mL glass graduated cylinder
  • 125-mL Erlenmeyer flask
  • 25-mL Erlenmeyer flask
  • Glass stirring rod
  • Medium stir bar
  • Metal tweezers
  • Pasteur pipette bulb
  • Melting point capillary tube
  • Glass funnel with small stem
  • Boiling chips
  • 50-mL glass beaker
  • Acetanilide (99% purity)
    20 mg
  • Acetanilide (>99% purity)
    20 mg
  • trans-cinnamic acid (98% purity)
    20 mg
  • trans-cinnamic acid (>99% purity)
    20 mg
  • Ethanol, absolute
    100 mL
  • 50-mL glass bottle with solvent-resistant cap
  • 50-mL glass graduated cylinder
  • Glass funnel
  • Pasteur pipettes
    Dependent on lab size
  • 70-mm filter paper
    1 box
  • 110-mm filter paper
    1 box
  • Analytical balance (at least 1)
    Dependent on lab size
  • Weighing boats
    Dependent on lab size
  • Spatulas
    Dependent on lab size
  • Melting point analyzer (at least 1)
    Dependent on lab size
  • Deionized water
    Dependent on lab size
  • Crushed ice
    Dependent on lab size
  • Ice container
    Dependent on lab size
  • Ice scoop (minimum 1)
    Dependent on lab size
  • Lab wipes
    Dependent on lab size

Lab Prep

Source: Lara Al Hariri at the University of Massachusetts Amherst, MA, USA

  1. Preparation of the Laboratory

    Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.

    • To set up for this lab experiment, wear the appropriate personal protective equipment, including a lab coat, chemical splash goggles, and gloves.
    • Confirm that the lab has a glass waste container and a container for solid acetanilide and trans-cinnamic acid waste.
    • Prepare 40 mL of a 95% by volume ethanol solution. Measure 38 mL of absolute ethanol and pour it into a 50-mL glass bottle using a funnel.
    • Then, add 2 mL of deionized water to the bottle. Mix the solution with a glass rod or by shaking the closed bottle until it appears homogeneous.
    • Label the bottle and place it in a fume hood for solvents. Store the absolute ethanol in a cabinet for flammable materials.
    • Set aside high-purity acetanilide and trans-cinnamic acid to be used as seed crystals.
    • Bring reagent-grade acetanilide and trans-cinnamic acid to the balances for students to use. Confirm that there are enough lab wipes, spatulas, and weighing boats.
    • Set out the following glassware and equipment at each student lab station:
       1    Lab stand
       1    3-prong clamp
       1    Stirring hotplate
       1    Pair of flask tongs
       1    Vacuum pump (or house vacuum)
       1    125- or 250-mL filter flask
       2    Büchner funnels
       1    Filter adapter
       2    600-mL beakers
       1    250-mL beaker
       2    5-mL graduated cylinders
       1    10-mL graduated cylinder
       1    125-mL Erlenmeyer flask*
       1    25-mL Erlenmeyer flask
       2    Glass stirring rods
       1    Medium stir bar
       1    Pair of tweezers
       2    Pipette bulbs
      *Note: Try to use older flasks with scratches on the inside for this lab.
    • Keep extra 125-mL Erlenmeyer flasks, stemless or wide-stem glass funnels, large filter papers, small beakers, and boiling chips available in case students need to hot filter their acetanilide solutions.
    • Place boxes of laboratory wipes, medium filter papers, and Pasteur pipettes in a central area for the students.
    • Set up the melting point analyzer and place a container of capillaries next to it.
    • Just before the lab, fill an insulated cooler with about 8 L of crushed ice. Place the cooler and an ice scoop on the central bench in the lab.

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