Inorganic Chemistry 

 Experiment 4

Spring 2018

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 Infrared and Electronic Spectra

    In experiment two, you found correlation tables for organic and inorganic compounds.  In this experiment, you will obtain the IR and visible spectra for an unknown compound.  From this data, you will identify the class of compounds from a list of unknowns.

IR study
    Obtain an unknown to be run on the Nicolet iS10 FT-IR spectrophotometer.  The sample will be run as a Nujol mull.  The mull is prepared by placing enough sample to thinly cover a dime in Description: Description: Description: Description: Description: C:\Users\mdraganj\Documents\draganjac_files\Midac.JPGyour mortar (the bowl) and grind with the pestle.  Then add a drop of Nujol (or mineral oil) and grind again.  You want to have a sample with the consistency of tooth paste.  Adjust by adding either more sample or mineral oil.  Place a small drop of the mixture in the center of the NaCl salt plate (use gloves when handling the salt windows to avoid contamination) and cover with the second salt plate.  Gently push the two salt plates together to spread out the sample.  Be careful not to make the sample too thick or too thin. For reference, you should obtain the IR spectra for NaNO3 and Na2SO4.
    Clean the salt plates with acetone.  Do NOT use water on the salt plates.

Visible spectrum
    The visible/ultraviolet spectrum is associated with electronic transitions in the compound.  In the transition metal complexes, many of these transitions occur in the visible region of the spectrum.  The spectrum obtained here is unlike the IR spectrum, in that it does not give "fingerprint" regions that aid in the structure determination.  However, once a spectrum is known, it is indicative of that Description: Description: Description: Description: Description: C:\Users\mdraganj\Documents\draganjac_files\visible.jpgparticular compound.  Many transition elements do have characteristic colors in solution.  Once you obtain your spectrum, be sure to discuss the relationship between the color of the solution and the absorbance maxima in the spectrum.  (Hint:  find the visible light spectrum with the corresponding wavelengths for the different colors).
    Sample preparation:  dissolve approximately 30 - 50 mg of sample in approximately 5 mL of water. The exact concentration is not important for this experiment.  Place the sample in a cuvette and obtain the spectrum using the HP8452A spectrophotometer. Print the spectrum.  Be sure to turn off the lamp when finished.  Do not use organic solvents to clean the plastic cuvettes.  Rinse with distilled water and let air dry.

    The report must follow the guidelines on the Lab Report page.  The minimum report should include an introduction explaining how each instrument works (in theory) and what information each instrument gives about the compound, the spectra and a discussion of your results.  The report will be due by 5:00 pm on Friday, March 16, 2018.  This lab will be worth 30 points of your lab grade. No late reports will be accepted.

Possible Unknowns

















Colors of hydrated metal ions (from Wulfsberg, Principles of Descriptive Inorganic Chemistry, p. 33)

Ti+3, violet

Ce+3, colorless 

Pa+4, colorless

V+3, blue 

Pr+3, green

V+2, violet 

Nd+3, lilac 

U+3, red-brown

Cr+3, violet 

Np+4, yellow-green

Cr+2, blue 

Pm+3, pink

Np+3, purple


Pu+4, tan

Mn+2, pale pink

Sm+3, yellow 

Pu+3, blue-violet

Fe+3, pale purple

Am+4, red

Fe+2, pale green

Eu+3, pink

Am+3, pink

Sm+2, red 

Cm+4, yellow

Co+2, pink

Gd+3, colorless

Eu+2, colorless

Ni+2, green 

Tb+3, pink

Cu+2, blue

Dy+3, yellow

Ho+3, yellow

Er+3, lilac

Tm+3, green

Yb+3, colorless

UO2+2, yellow
Zn+2, colorless

CHEM4204 Experiment list