Title: Infrared Spectroscopy (IR) Lab
1Infrared Spectroscopy (IR) Lab
- Infrared Spectroscopy Identification of Unknown
- The use of selected physical properties and
Infrared Spectroscopy to determine the identity
of an unknown compound. - Text Materials
- Slayden pp. 33 - 44
- Pavia pp. 851 885 (Infrared Spectroscopy)
- pp. 941 - 959 (Mass
Spectrometry) - pp. 719 - 729 (Simple Distillation)
- Solomons Sec. 2.16 9.12 - 9.14
- Lecture Slides (Dr. Schornick Web Site)
- URL http//classweb.gmu.edu/jschorni/irlecture.p
pt
2Infrared Spectroscopy (IR) Lab
- Elements of the Experiment
- 1st Week
- Lecture on Theory of
- Infrared Spectroscopy
- Mass Spectroscopy
- Ultraviolet / Visible Spectroscopy
- 2nd Week
- Determination of Unknown Physical Properties
- IR Spectrum of Unknown
- Spectroscopy Problem Set
- Will be E-Mailed by Instructor
- Due Date to be Determined
3Infrared Spectroscopy (IR) Lab
- Physical Properties of Spectroscopy Unknown
- Boiling Point Purification via Simple
Distillation - Physical Description of Purified Unknown
- Solubility Relative to Water
- Density Relative to Water
- Refractive Index (Corrected for Temperature)
- Infrared Spectrum Analysis
- Analysis of Results identification of Unknown
- Unknown List Slayden Manual, Appendix 3, p.
125-127 - Verify physical properties with appropriate
literature citation (Merck, CRC, etc.). - The literature citation for a compound must
include the item number, if applicable, and page
number
4Infrared Spectroscopy (IR) Lab
- Simple Distillation Background
- Note The Distillation process (Simple and
Fractional) will be formally introduced in a
later experiment - Simple Distillation will be introduced here as
part of the Spectroscopy experiment to purify the
sample and determine its Boiling Point - Distillation, like Spectroscopy, Melting Point,
Refractive Index, etc. is one of the tools we
introduce you to in the Organic I II courses - Boiling point and purification of a sample by
Simple Distillation is one of several physical
properties solubility density relative to
water, refractive index, melting point that you
will determine routinely on sample unknowns
5Infrared Spectroscopy (IR) Lab
- Simple Distillation Background (Cont)
- Single Vaporization / Condensation cycle of a
liquid sample - The Distillate for a mixture is always impure at
any temperature range between the range of
boiling points of the components - Therefore, it is impossible to completely
separate the components in a mixture with simple
distillation. - Relatively pure substances can be obtained from a
mixture with Simple Distillation, if the boiling
points of the components differ by a large amount
(gt100oC) - Redistilling the distillate from multiple
sequential vaporization-condensation cycles
would produce increasingly pure substances, but
this is a very tedious process.
6Infrared Spectroscopy (IR) Lab
- Simple Distillation Background (Cont)
- Samples of unknown organic compounds that
students receive in Organic Lab are generally
pure, but may contain some impurities that could
produce ambiguous results when determining the
chemical or physical properties of the compound - Simple Distillation is used to purify the sample
by separating the pure compound that comes over
in a narrow temperature range corresponding to
its boiling point from the impurities that have
boiling points lower than or higher than the
compound
7Infrared Spectroscopy (IR) Lab
- Simple Distillation Basics Steps
- Set up Simple Distillation apparatus (next slide)
- Heat sample and collect - in a waste beaker - all
distillate that comes over while the temperature
continues to rise.Usually this involves only a
small amount, if any, of the distillate. - When the temperature stabilizes over a narrow
temperature range collect the distillate in a
small clean container. The bulk of the sample
will be collected here. - Stop collecting sample when the temperature
begins to rise again, i.e., any sample remaining
at this point would consist of impurities with
boiling points above that of your unknown sample.
8Infrared Spectroscopy (IR) Lab
- Typical Distillation Setup
9Infrared Spectroscopy (IR) Lab
- Simple Distillation Procedure
- Set up Simple Distillation apparatus
- Use 25 mL or 50 mL Distillation flask
- Place a Corundum or Teflon boiling chip in the
flask - Start gentle water flow through condenser
- Put a waste receiving container (small beaker)
into an ice water bath especially for low
boiling liquids. - Begin heating sample
- Note The sample may appear to be boiling, but
the actual boiling point is not reached until the
temperature of the boiling liquid and the vapor
surrounding the thermometer bulb reach
equilibrium. At this point the vapor will start
to condense in the condenser
10Infrared Spectroscopy (IR) Lab
- Simple Distillation - Procedure
- Note the temperature when the distillate begins
to drip into the waste receiving container - Continue to collect distillate in the waste
container until the temperature begins to level
off - Remove the waster container and begin collecting
the distillate in a small clean Erlenmeyer flask - Note the temperature when you start to collect
the purified sample - Continue to collect the sample until the
temperature begins to rise again (it may not
change before the all of the sample has come
over) - Note the temperature just before the temperature
begins to change - The first and last temperatures recorded in the
narrow boiling range represent the boiling point
range of your sample
11Infrared Spectroscopy (IR) Lab
- Solubility Density Relative to Water
- Place about 2 mL Distilled Water in a medium test
tube - Add 4-5 drops of the solid or purified liquid
unknown - Shake test tube firmly
- Observe solubility of Sample in Distilled Water
- If sample is insoluble, observe whether sample
- Floats on top of water
- Floats in the middle of the water
- Sinks to the bottom of the test tube
12Infrared Spectroscopy (IR) Lab
- Refractive Index
- Clean prisms of ABBE Refractometer with tissues
Methyl Alcohol BE GENTLE!! - Do not touch prism with fingers or other hard
objects, use tissues - Place 3-4 drops of sample on Prism.
- Close Prism and raise lamp in front of Prism
Portal. - Flip switch on left side to turn on light.
- Use large dial on right to bring light/dark image
into view. - If image cannot be found, flip switch on left
down and use large dial on right to bring the
Scale into view around 1.4000
13Infrared Spectroscopy (IR) Lab
- Refractive Index (Cont)
- Release switch on left and use large dial on
right to bring light/dark image into view - Sharpen line of demarcation using Drum dial on
front of instrument. - Use Eyepiece to sharpen Cross-Hairs
- Align the line of demarcation with the
Cross-Hairs - Flip switch on left down and read value to 4
decimal places - Ex. 1.5523
14Infrared Spectroscopy (IR) Lab
- The following equation adjusts the raw Refractive
Index value to 20oC - ND20 NDRm Temp (Rm Temp 20) 0.00045
- Ex For an observed value of 1.5523 at 16oC,
the correction is - ND20 1.5523 (16 20) 0.00045 1.5523
(-4) 0.00045 1.5505
15Infrared Spectroscopy (IR) Lab
- Infrared Spectroscopy
- Liquid Samples
- 1 to 2 drops of liquid sample are placed between
two single crystals of sodium chloride (Salt
Plates) - Note NaCl plates are water soluble keep
dry - Solid Samples Soluble in Acetone
- Dissolve sample in acetone
- Evaporate on Salt Plate
- Solid Samples Not Soluble in Acetone
- Make Potassium Bromide (KBR) pellet
- Put Salt Plate sandwich in Plate Holder
- Place Plate Holder into Beam Slot of IR
Spectrometer
16Infrared Spectroscopy (IR) Lab
- Infrared Spectroscopy Cont
- Confirm with instructor that Background has
been scanned in. - Select Memory location (X, Y, or Z)
- Press SCAN button
- Verify No. of Scans is 4 if not, notify
instructor - Press Execute (last (far right) soft button
- If spectrum absorptions bottom out, remove Salt
Plate holder and reload Salt Plate with less
sample. - Rerun Scan / Execute again
- Push Plot to produce chart
- Remove Cell Holder and disassemble
- Clean Salt Plate with acetone and dry with
ChemWipe - Place Salt Plate in desiccator