CHM 221-02, 03 – Lab Tests for Functional Groups
Overview and Instructions for the Lab Report
Posted: Monday, Nov. 2 (due Wednesday, Nov. 11)
Determination of the structure of an organic compound can be done with a variety of techniques. Besides elemental analysis, spectroscopic methods can identify specific bonding groups based on the energy of absorption. This is often done by infrared spectroscopy in the so-called fingerprint region of 1000 to 3800 cm-1. Nuclear magnetic resonance (NMR) for the 13C and 1H atom also shows unique structural units based on the magnetic energy interactions.
Laboratory reagents are often used in conjunction with instrumental methods, and preliminary tests can be performed to classify an unknown compound. Sample purity can also be evaluated, and the sample itself may need to be purified for analysis. For example, we have already seen that melting point range is one simple test for identification of the compound and its purity.
In this lab we will look at two more examples: (1) solubility as a preliminary test for various functional groups ; (2) bromine and permanganate tests for identification of unsaturation in a compound.
Report – Instructions
The lab report has two parts.
In Part 1, you will need to research the structure of the compounds listed in the table. You will then evaluate the solubility of each compound based on its polarity compared to the polarity of the solvent listed. Complete the chart, and write the structures of all the substances listed there.
In Part 2, you will watch the video for the tests for unsaturation. Bromine addition is a common reaction for alkenes, as we have studied. Alkanes do not react with Br2. Permanganate (violet), MnO4 -1 will also add to a double bond with the product, MnO2 (brown).
Each part has questions for you to answer.
Lab Report – Part I – Solubility
Draw a structure for each of the compounds (all solids and solvents). Complete the following table by classifying each solid as either “soluble” or” insoluble” in the solvent.
TEST SOLID SOLVENT
4-amino-1-naphthalene sulfonic acid
1.) Explain your reasoning in the solubility of resorcinol in the three solvents. Include your evaluation of the overall polarity of each substance (with electronegativity values).
2.) What is the difference in solubility characteristics between acetic acid and heptanoic acid? What is the effect on solubility of the length of the carbon chain for these two carboxylic acids?
Lab Report – Part II – Tests for Unsaturation
Watch the two videos for these tests. Answer the following questions.
1.) What are the solubility characteristics of Br2? Explain how and why it separates when added to a hydrocarbon, particularly from the aqueous layer.
2.) Write an equation for the chemical reaction of 1-hexene with
3.) In this list of hydrocarbons,
(a) identify the ones which have unsaturation and will react with the two reagents in these two tests:
(b) List four hazardous chemicals in these two tests.