Recrystallization
At the end of this lab, students should know...
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Q1: What personal protective equipment is required for a recrystallization lab?
Students must wear a lab coat, chemical splash goggles, and gloves during recrystallization experiments. These items protect against chemical exposure and potential splashes from organic solvents and hot solutions. Ensure all equipment is in good condition before beginning work to maintain a safe laboratory environment.
Q2: How do you prepare a 95% ethanol solution for recrystallization?
Measure 38 mL of absolute ethanol and pour it into a 50-mL glass bottle using a funnel. Add 2 mL of deionized water to create the 95% ethanol solution. Mix thoroughly with a glass rod or by shaking the closed bottle until the solution appears homogeneous, then label and store in a fume hood.
Q3: What glassware and equipment should be set up at each student lab station?
Each station requires a lab stand, stirring hotplate, two 600-mL beakers, one 250-mL beaker, Erlenmeyer flasks, graduated cylinders, glass stirring rods, Büchner funnels, a filter flask, and a vacuum pump. Additionally, include flask tongs, tweezers, pipette bulbs, and a medium stir bar. This setup enables students to perform heating, cooling, and vacuum filtration steps efficiently.
Q4: Why are high-purity crystals set aside separately in recrystallization preparation?
High-purity acetanilide and trans-cinnamic acid are reserved as seed crystals to initiate crystallization during the experiment. Seed crystals provide nucleation sites that promote controlled crystal growth. Reagent-grade compounds are used for the bulk of the experiment, while pure seeds ensure quality crystal formation.
Q5: What waste containers and materials should be prepared before the lab begins?
Prepare a glass waste container and separate containers for solid acetanilide and trans-cinnamic acid waste. Confirm these containers are available and properly labeled before students arrive. Proper waste segregation prevents contamination and ensures safe disposal of chemical materials used during recrystallization.
Q6: How should the laboratory be organized for efficient student workflow?
Place boxes of laboratory wipes, medium filter papers, and Pasteur pipettes in a central area for shared access. Set up the melting point analyzer with capillaries nearby for analysis. Fill an insulated cooler with crushed ice and position it on the central bench. This organization minimizes congestion and allows students to access common supplies quickly.
Q7: What backup glassware and equipment should be available during the recrystallization lab?
Keep extra 125-mL Erlenmeyer flasks, stemless or wide-stem glass funnels, large filter papers, small beakers, and boiling chips available. These backups accommodate students who need to perform hot filtration or encounter breakage. Having contingency supplies ensures the lab can continue smoothly without interruption.