Lab IV:
Part 2 of 3-Week Dual Unknown Lab
NOTE:
As stated in Lab 1, 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.
Pre-lab
Work
Reading
Assignment:
- Introduction
to Functional Groups:
Hornback; pp. 50-53
- Infrared
Spectroscopy:
Appendix
& Mohrig, Technique 18.1-18.4, pp. 228-236 & 18.6-18.9, pp. 243-267.
- Polarimetry:
Appendix
& Mohrig, Technique
14.1-14.4, pp. 165-172.
- Refractometry
Appendix
& Mohrig,
Technique 13 pp. 161-164.
- Solubility Tests:
Appendix
Solubility
Tests
These tests help you to determine the
nature of your unknown compounds. They show if you have a strong acid,
a weak acid, a strong base or a neutral substance. 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, refractometry,
and polarimetry
to collect more physical property information about your unknowns.
Experimental
Work
Objectives:
1. To determine the solubility/reactivity of your compounds.
2. To learn how to use infrared spectroscopy, polarimetry, and refractometry
to obtain information about the physical properties of a compound.
Experimental Procedures
Solubility
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 notebook.
Sample Handling for Instrumental Analysis
IMPORTANT NOTE:
- For infrared and
refractive index, use pure (neat or undiluted) samples.
- 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.
Calculate the specific
rotation for each unknown using the exact concentration you
calculated previously for your 1% solution.
Prepare an IR data
table for each unknown. List ALL possible functional groups and,
using the other data you have collected on your unknown, highlight
the functional groups which are most likely to be present. For liquid
unknowns only:
Obtain a refractive index for you liquid unknown making sure to note the temperature
as well.
Calculate the
refractive index for your liquid unknown at 20oC.
**Be sure to
share a copy of your IR spectrum as well as your
calculated
values for specific rotation and refractive index with your partner.
Post-lab Work
1. Write equations
to show what happens when...
(a.)...an amine dissolves in dilute, aqueous HCl.
(b.)...a carboxylic acid dissolves in dilute, aqueous NaOH.
(c.)...a carboxylic acid dissolves in dilute, aqueous NaHCO3.
(d.)...a phenol dissolves in dilute, aqueous NaOH.
Type the answers
to the following questions(#2-6) and tape the answers into your notebook.
2. From the solubility
data, identify the functional groups that are possible for each unknown.
3. From the FT-IR
data, identify the functional groups that are possible for each unknown.
4. What does each
instrument tell us about a compound?
5. Discuss any errors
in your experiment and what you would do differently if you were to do
this lab again.
6. Summarize the
information about each unknown compound.
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