Recrystallization

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VIDEO LINKS:

Technique Experiments (Write protocols and perform techniques based on these):

  1.  Purification with Activated Charcoal
  2. Choosing a Solvent for Recrystallization
  3. Recrystallization
  4. Collecting Crystals after Recrystallization

Lab Experiments (Write protocols and perform experiments based on these):

  1. Select an appropriate solvent for benzoic acid. Test the following solvent choices: acetone, ethanol, ethyl acetate, and water.
  2. Perform a recrystallization of 1 g impure benzoic acid. Calculate how much of your solvent is needed. Perform a hot filtration and/or decolorization if necessary.
  3. Collect and dry the product; determine yield and melting point of both the crude and recrystallized benzoic acid.

The prelab must include Experimental Protocol, Chemical Table and Equipment Table.

The lab report requires all sections (including prelab sections) to be completed in one document.

Experimental Protocol

(Analysis) Watch the experiment videos. Take notes on the protocolfor both the technique and theexperiment. Stop the video and re-watch as necessary to acquire the details of the procedure. Writeout the protocol for each part of the experiment. (It can be written in sequential steps. Completesentences are not necessary.) This is the protocol you will follow, so be detailed.

Chemical Table

(Representation) Prepare your chemical table including the materials you will use in the experiment and any products generated.  Here is a general template that you may use.
Chemical Name Chemical Formula Structural Formula Molar Mass (g/mol) Hazards Reference Precautionary Statements
Acetone C3H6O 58.08 Flammable liquid, eye damage, target organ toxicity (central nervous system, kidney, liver, spleen, blood) fishersci Use in fume hood; Keep away form heat/sparks/open flames.
           
           
           

Equipment Table

(Analysis) Identify the equipment (type AND size) needed for the experiment and include the name and an image of each.  Be sure to describe the equipment, how to use it, and why it is suitable for this use.
Equipment Name Equipment Picture or Description Intended Purpose

Data Collection

  1. (Acquiring competencies) Following your detailed protocol based on the videos, perform all the experiments. Record your observations and take pictures of your key steps in the process. Your observations and images need to be incorporated in your data section and this section should be as detailed as possible as you will use this information to complete your discussion.
  2. (Acquiring competencies) Follow your detailed protocol based on the videos. Record your observations for Choosing a Solvent for Recrystallization.
Solvent Soluble at room temperature? Soluble at elevated temperature? Appropriate solvent for recrystallization?
acetone
ethanol
ethyl acetate
water
 
  1. (Acquiring competencies) Follow your detailed protocol based on the videos. Record your observations for Recrystallization.
  2. (Acquiring competencies) Following your detailed protocol based on the videos. Record your observations for Collecting Crystals after Recrystallization. Include your percent recovery, and the melting point of the purified product versus the crude product.
  3. (Representation) Fill out the following table with your data.
Melting point of crude benzoic acid Melting point of recrystallized benzoic acid

Data Processing

  1. (Representation) Draw the structure of benzoic acid.
  2. (Analysis) Classify benzoic acid as polar or non-polar based on its structure.
  3. (Analysis) Match the polarity of benzoic acid to the polarity of the solvent choices investigated.
  4. (Analysis) Provide at least one argument for water being a good solvent choice based on molecular structure.
  5. (Manipulation) Show your calculation to determine your percent recovery.
  6. (Existing knowledge, research and view) Provide the literature values for the solubility of benzoic acid in water at 100°C and at room temperature.
  7. (Manipulation) Calculate the amount of benzoic acid dissolved at room temperature assuming 1.00 g of benzoic acid and 20 mL of deionized water.
  8. (Manipulation) Calculate the amount of benzoic acid dissolved at 100°C assuming 1.00 g of benzoic acid and 20 mL of deionized water.
  9. (Manipulation) Calculate the maximum amount of benzoic acid in grams that would precipitate under the conditions of your recrystallization. (HINT: This is your theoretical yield for the recrystallization.)
  10. (Manipulation) Using the mass of recrystallized benzoic acid and the theoretical yield for your recrystallization, calculate the percent yield for the recrystallization.
  11. (Assumptions)
Assumptions made Testing the assumption If assumptions are wrong ...
Water is the best solvent choice Try other solvents or solvent mixtures A higher percent recovery is obtained with another solvent choice
     

Discussion

Write a minimum one-page (12 font, single spaced) discussion on the experiment conducted this week. Address as many questions as you can from each category as fully as possible integrating the collected data, providing explanations for the observed trends, and evaluating whether your original assumptions about the experiment were validated by the results. The assignment will be graded on completeness, clarity of the explanations and the meaningful integration of the collected and calculated data. Correct grammar and appropriate format for the chemical formulae and chemical reactions is expected.
  1. (Interpretation) Describe the meaning of the solubility value and its unit as it applies to this experiment.
  2. (Analysis) Using the solubility at the different temperatures, comment on any observable trends in the solubility of benzoic acid in water as a function of temperature.
  3. (Analysis) Provide at least two arguments for using water as the solvent choice (of those tested) for the benzoic acid recrystallization.
  4. (Acquiring competencies) Comment on potential changes in the purity of your final crystals, if the solution is left to evaporate instead of performing the filtration.
  5. (Existing knowledge, research and views) Describe the conditions when it is preferred to let the crystals dry at room temperature, in an oven at a low heat setting, or in an oven at a high heat setting.
  6. (Analysis) Provide at least one argument for what your observed melting points indicate about the purity of your sample before and after recrystallization.
  7. (Analysis) Provide at least one supported argument for a recovery greater than 100%.
  8. (Analysis) Describe what would happen if you added less solvent than needed to dissolve your compound at the elevated temperature.
  9. (Analysis) Describe what would happen if you added more solvent than needed to dissolve your compound at room temperature.
  10. (Analysis) Provide an argument to explain a much lower than expected melting point for the recrystallized product.
  11. (Analysis) Describe what would happen, if you used a compound with a melting point of 60°C instead of benzoic acid in this experiment.
  12. (Experiment design) Propose a method for completing a recrystallization for a compound with a melting point of 60°C.
  13. (Analysis) Other than solubility at cold versus hot temperatures, identify some other considerations to make when selecting an appropriate crystallization solvent.