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Lab IV: Part 2 of the 2-Part Dual Unknown Lab
Pre-lab Work
Reading Assignment:
- Introduction
to Functional Groups:
Hornback; pp. 50-53 - Infrared
Spectroscopy:
Appendix, including the web tutorial Infrared Spectroscopy and Organic Functional Groups& Mohrig, 2nd edition, Technique 18.1-18.4, pp. 228-236 & 18.6-18.9, pp. 243-267 or 3rd edition Techniques 201.-20.4 pp. 277-285. - Polarimetry:
Appendix & Mohrig, 2nd edition Technique 14.1-14.4, pp. 165-172, or 3rd edition Techniques 16.5-16.7, pp. 203-211. - Solubility Tests:
Appendix - Mass Spectrometry:
Hornback, pp 617-633. - Mass Spectrometry:
Appendix for GC/MS only & Mohrig, 2nd edition Technique 20.1-20.2, & 20.5, pp. 341-349, 353-358 or 3rd edition Techniques 23.1-23.2, &23.5, pp. 406-413, 417-422.
Pre-lab Questions:
(Please turn in the answers to these questions when you arrive to lab.)
1. Here is the data for my unknown when put through the solubility tests. Being thorough, I tested the unknown in ALL of the possible solutions given in lab:
--In distilled water, the unknown was insoluble with no change to the pH paper.
--Insoluble in 5% HCl
--Soluble in 5% NaOH
--Soluble in 5% NaHCO3
From the list of possible major functional groups listed in the Introduction below, what possible major functional group(s) are present on my unknown based on these results?
2. Using your new bff—ChemDraw! please show the reaction that takes place between phenol and 5% NaOH(aq) to produce the phenolic salt and water.
3. Typically, organic compounds are insoluble in water. What kind of organic compounds are soluble in water?
4. Please describe, IN DETAIL, how you would prepare a 1% (g/mL) ethanolic solution of your unknown for the polarimeter using a 25.00-mL volumetric flask, pure Ethanol (absolute Ethanol), your unknown, and any other glassware in the lab. [Note: your pure liquid unknown can be massed, just like your pure solid unknown.]
5. How many degrees of unsaturation (DU) are present in the following compounds?
a. C6H9Cl b. C4H8O c. C6H7N
6. Using the mass spectra supplied in lecture for each unknown, please give the following information for each unknown:
a. Molecular weight.
b. Any other information about possible functional groups or likely fragments off of the unknown.
7. For each structure below, state several significant masses (Molecular ions are 'significant masses' too!) that would be seen in the mass spectrum for each compound:
Compounds: |
Mass Fragments (m/z) in MS: |
|
|
1. |
3.
|
|
1. |
3. |
|
1. |
3. |
Introduction
NOTE: As stated in Lab 3, each unknown will contain one or more of the following major functional groups: ALCOHOL, ALDEHYDE, AMINE, CARBOXYLIC ACID, KETONE, NITRILE, PHENOL.
The unknown might also contain one of these other functional groups: alkene, alkyne, amide, aromatic, ester, ether, halide, and nitro.
Beilstein Test
This test provides you with information about whether your unknown contains a halide, specifically a
Solubility
Tests
These tests help you to determine the
nature of your unknown compounds. First, you will practice the solubility tests with compounds whose functional groups are known to you. You will then test your unknowns to see if you have a carboxylic acid (a stronger organic acid), a phenol (a weaker organic acid), an amine (an organic base), or a neutral compound. With this information,
you can narrow down the possible major functional groups that could exist
as components of your unknown compounds.
Click here for specific procedures.
Instrumental
Techniques
It is often necessary in organic chemistry to use instrumental techniques
to identify compounds or characteristics of compounds. Many of these
techniques
are used to determine physical properties of compounds in order to make
the identification of unknown compounds easier. For Part 2 of your Dual
Unknown lab, you
will be using infrared
spectroscopy in lab to collect more physical property information about your unknowns.
You will be supplied with the mass spectrum of each unknown in a previous lecture. Please analyze the mass spectra data before coming to lab. This will make it easier to perform a cursory identification of each unknown at the end of lab when you are given the list of possible compounds for your unknowns. (Note: In Lab 6 you will obtain your own GC/MS data in lab from our GC/MS instrument.)
Safety Notes The acids and bases used in the solubility tests are corrosive to the skin and eyes. Wear gloves and goggles when handling these compounds. Wash immediately with cold water in case of a spill. |
Experimental
Work
Objectives:
1. To determine the solubility/reactivity of your compounds.
2. To learn how to use infrared spectroscopy and polarimetry
to obtain information about your compounds.
3. To test for the presence of halide using the Beilstein Test.
4. To perform the Beilstein Test for Halides on your 2 unknowns.
5. To use the mass spectra for each of your unknowns that you obtained in a previous lecture to determine the molecular weight and possible molecular formula for each of your unknowns.
6. To obtain the list of possible unknown compounds and work with your partner(s) to make an attempt at a cursory identification of your unknowns.
Experimental
Procedure
Solubility Tests
The determination of the solubility in
water is the starting point, and is perhaps the most important solubility
test. The pH of the water-solubility test should always be determined. Why?
Record your solubility data neatly in a table in your e-lab.
Infrared Spectroscopy & Polarimetry
IMPORTANT NOTE:
- For infrared spectroscopy: use pure (neat or undiluted) liquid and solid samples and create an electronic version of your IR spectrum that can be copied to one of the designated "ORGO lab flash drives" for portability to your laptop and your partner's laptop.
- For polarimetry: Prepare approximately a 1% (weight/volume, g/mL) solution of sample in ethanol. Use a balance (recording the amount you weigh out) and a 25.00 mL volumetric flask. Calculate the exact concentration of the solution you prepare.
For both
unknowns:
Prepare a 1% ethanolic solution of your unknown for the polarimeter and
use your pure unknown for the infrared spectrophotometer. Please see
your
Instructor
for directions
on how to use the instruments.
Measure the observed rotation of each unknown using your prepared 1% ethanolic solution. Calculate the specific rotation for each unknown using the exact concentration of your "1%" solution.
Prepare an IR data table for each unknown. List ALL possible functional groups using the literature table in the infrared spectroscopy section of the appendix. Highlight the functional groups which are most likely to be present, i.e.-match your data the best.
**Remember...please be sure to share an electronic copy of your IR spectrum with your partner.
Beilstein
Test
Follow the procedure described in the Appendix.
Test 1-butanol, one of the chlorides or bromides provided as standards, and your unknowns from your Dual Unknown lab. Record your results in your e-lab.
Mass spectra
Supplied to you in a previous lecture and hopefully, analyzed before coming to this lab to determine the most likely molecular weight for your unknowns as well as any possible fragments/pieces that must be part of the unknowns.
How to Obtain the List of Possible Unknown Compounds:
To obtain the list of possible unknown compounds, you and your partner(s) need to present an oral argument for the major functional group(s) you think are present in your unknowns using the data collected in this lab and the molecular weight of your unknowns based on the analysis of your mass spectra that you've been given in a previous lecture. Once I'm satisfied that you and your partner have a clear vision of your unknowns, I'll supply you with a hardcopy data table containing all the possible unknown compounds grouped according to their major functional group(s). Then, you and your partner can attempt to make a cursory identification of each of your unknowns before leaving lab.
Waste Disposal and Clean-up
- Dispose of your acid and base solutions from the solubility tests in their respective waste containers.
- Place any halogenated waste in the non-flammables (halogenated) waste bottle and any non-halogenated (flammable) waste in the flammables waste bottle.
- Place the used test tubes in the glass disposal box.
- Rinse your glassware with acetone and dispose of the acetone rinse in the flammables waste bottle.
Post-lab Work for the Dual Unknown Lab
**Please write a 500-word max. Dual Unknown lab conclusion and submit one hardcopy version for you and your partner(s) no later than 5PM on Tuesday, 6/18.
Please place all spectral data and data tables in an "Appendix" to your conclusion and reference the data as you use it throughout your 500-word max. conclusion when arguing for the identification of each unknown.
NOTE:
You can only go over the 500-word limit if you are working in a group of 3 with 3 unknowns OR you make your conclusion so creative that I can't wait to read more of it...like a great story! :)
Please put the answers to the following questions at the very end of your "Appendix".
1. Using a data table and the seven possible major functional groups mentioned in the Sudoku functional group puzzle and our online lab manual, please answer each question below for EACH of your unknowns:
a.) Which major functional groups are possible based on the solubility data?
(Please report your solubility test data to support your answer.)
b.) Which major functional groups are possible based on the FTIR data?
c.) Looking at the Solubility data and FTIR data, which functional group(s) are present in both pieces of data?
2. What was the observed and corrected optical rotation for each unknown? Please show your calculations.
3. In the table below, write the 'protonation state' (i.e.-neutral, protonated or deprotonated) of a carboxylic acid (RCOOH), a phenol (PhOH), a primary amine (RNH2) and an alcohol (ROH) in each of the solutions listed.
RCOOH |
PhOH |
RNH2 |
ROH |
|
| 5% HCl (pH < 2) | ||||
| 5% NaOH (pH > 12) | ||||
| 5% NaHCO3 (pH ~ 9) |
4. Would you expect a solid carboxylic acid, phenol, primary amine, or alcohol to dissolve in the 3 solutions listed? List your answers ("yes"=it dissolves, or "no"=it does not dissolve) in the table below.
RCOOH |
PhOH |
RNH2 |
ROH |
|
| 5% HCl (pH < 2) | ||||
| 5% NaOH (pH > 12) | ||||
| 5% NaHCO3 (pH ~ 9) |
5. Why were you instructed to only test the pH in the water solubility test and not in any of the other acid/base solubility tests?
6. What does the polarimeter tell us about a compound?