Appendix
35 Identification of an Unknown Organic Solid–Planning Scenario and Background
Scenario
In your new job as a chemical safety aide for MSU’s Office of Environmental Health and Safety (EHS), your team encounters an organic research laboratory that has recently “found” an unlabeled jar of a powdered mixture in the back of one of the chemical hoods. The lab manager has narrowed down the possibilities of what the organic powder might be, as listed below:
Possible Compounds
| acetanilide | benzoic acid | succinimide | adipic acid | benzilic acid |
| oxindole | benzamide | n-phenylsuccinimide | salicylic acid | cinnamic acid |
Your supervisor tasks your team with testing the powder, purifying it and identifying it. Since your team is responsible for safely disposing of the solid, you will also need to determine as many of its physical and chemical properties as possible to help prevent potentially dangerous interactions with the other waste in the facility.
Before you can identify the unknown, you will need to perform a recrystallization to ensure the purity of the sample. In order to perform the recrystallization, your team will need to perform solubility test in order to select the optimal solvent for your unknown.
Tasks for successfully completing this project
- Perform solubility test of your unknown at high temperature and at low temperature. Choose the best solvent and binary solvent system for recrystallization.
- Perform a single-solvent recrystallization and a binary-solvent recrystallization using solubility test results.
- Use two qualitative and two quantitative identification techniques to identify of the unknown.
- Share data with your group members and report the identity of your unknown to your TA; assess the validity of their claims based on the evidence from the identification methods.
You will be weighing out three grams of the compound; use it wisely! You and your TA will not be told the identity of your compound, nor will you be given any other information about it.
Safety notes:
● Be sure to consult the MSDS/SDS for any compound that you might work with.
● Wear safety goggles, gloves, and appropriate clothing at all times in the laboratory.
● Dispose of waste in the labeled containers. Do not pour any waste down the drain unless you check with your instructor first.
● Use great care when transferring solutions of acids and bases.
● If you spill a strong acid or base on your clothes or skin, rinse with large amounts of water immediately and ask one of your team members to tell your TA.
● All of the unknown compounds that you will work with in this project are Generally Recognized as Safe, but normal safety precautions should be observed.
Techniques you may need to learn or review
Consider reviewing the following sections in the Lab Manual:
- Measuring solids and liquids
- Purification via recrystallization
- Solubility test at different temperatures
- Measuring solution pH
- Melting point determination
- FTIR spectroscopy
- 1H NMR spectroscopy
Project Checklist
Use these questions as a guide to complete required tasks and lab documents. This planning scenario and background document should be uploaded to D2L for grading.
Optimization of solvent system
- Solubility Test: Five greener solvents are provided below. Your team must test the solubility for the unknown in all pure solvents at different temperatures and summarize the result in the solubility chart next week.
| Water | Ethanol | Ethyl Acetate | Toluene | Heptane | |
|---|---|---|---|---|---|
| Low temperature | |||||
| High temperature |
Note: you do not need to fill out this table. It is only a reference table to help you prepare for next week’s experiment. Think: how do you plan to collect the data?
- For each solvent that you will test, indicate whether the unknown is soluble when heated, when cooled and at room temperature. How can you control the temperature? What will occur if the temperature is too high?
- Based on the results of the example table below, which is the best solvent for recrystallization? What makes it a good solvent?
| Example | Solvent A | Solvent B | Solvent C |
|---|---|---|---|
| Ice bath | High solubility | Medium solubility | Low solubility |
| Room temperature | Medium solubility | Medium solubility | Medium solubility |
| Warm water bath | Low solubility | Medium solubility | High solubility |
- You need to write a procedure for finding the solubility of your compound. What information will you need to determine this? What factors affect solubility?
- Some organic solvent you used are highly flammable, for example, heptane. Be careful! How would you warm it up?
Recrystallization
- For single solvent recrystallization, each team must test at least one pure solvent for the unknown. For multi-solvent recrystallization, each team must test at least one binary mixture of solvents. Remember the two solvents you chose for multi-solvent recrystallization should be miscible. Indicate which solvents or solvent systems your team will try.
- For single-solvent recrystallization, what factors did you consider in this selection? How will you manipulate these to induce crystallization?
- To guide your thinking, consider organizing information on each solvent’s general polarity and boiling point, or any relevant properties of the selected solvents. Take the boiling point of each solvent into consideration.
- For multi-solvent recrystallization, what factors did you consider in this selection? How will you manipulate these to induce crystallization?
- What are the general steps for a single-solvent recrystallization and a binary-solvent recrystallization?
- Why should we be concerned about purity of the unknown before we attempt to identify it? How would an impurity affect the results of your identification techniques?
Identification of Unknown
- You will choose four techniques to analyze the unknown; justify those selections and describe how you will use the information from each technique to identify your unknown. Are they qualitative or quantitative techniques or both? Why?
- Based on the four chosen identification techniques, hypothesize how impurities could affect the results of these techniques. Be detailed.
Chemicals (add rows as needed)
| Chemical Name | Hazard(s) | Accidental Release Measures |
|---|---|---|
|
|
Equipment
Generate a detailed list of equipment you need, hand-draw the apparatus set-up for solubility test and recrystallization.
Project Plan (Procedures)
Write a preliminary plan for your experimental procedure for each week. Indicate what each person in your group will do to solve the problem, and what data they will record. Break down the work so you use your time effectively and that each person will end up with a mini lab report for their data and notes assignment next week. Be detailed.
