From: Dr Bob <drbob**At_Symbol_Here**FLOWSCIENCES.COM>
Subject: Re: [DCHAS-L] Perchloric acid use
Date: Tue, 21 Dec 2021 17:49:54 +0000
Reply-To: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU>
Message-ID: BN8PR07MB63409CA146A17A76EDD47A67D97C9**At_Symbol_Here**



Hi Elizabeth Hinds!


I have attached a link to a paper I wrote on perchloric acid a couple of years ago. You need to know this stuff can form contact-explosive organic peroxides in a variety of ways. Perchloric hoods with wash-down systems innundate and dissolve these peroxides, minimizing explosive hazard.


Thee following is a link to an article on this acid I wrote four years ago.


Be careful about narrowing your thinking about perchloric acid to whether a hood is required. Consider these equally important questions:

  1. Do you plan on diluting the acid in-house or will you purchase pre-diluted?
  2. Where will concentrated acid  be stored? (I note in procedure the concentrated acid is used with a dropper bottle)
  3. How will waste products left over after experiment be disposed of? Remember than as the damp stuff dries out, it could get more dangerous.
  4. Will you be using materials in an explosion-proof electrical environment?
  5. I am particularly distressed by the phraise in your procedure:  "The solutions should never be poured down the sink." I see no alternates discussed in the procedure.


Best wishes!


Dr. Bob Haugen

Director of Product and Technology Development

Flow Sciences, Inc.


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From: ACS Division of Chemical Health and Safety <DCHAS-L**At_Symbol_Here**Princeton.EDU> On Behalf Of Elizabeth Hinds
Sent: Tuesday, December 21, 2021 11:40 AM
To: DCHAS-L**At_Symbol_Here**Princeton.EDU
Subject: [DCHAS-L] Perchloric acid use


We have an inorganic chemistry lab that uses perchloric acid. 

Guidelines for using perchloric acid digestions state that a wash down fume hood must be used. In this procedure they are using diluted (0.1, 1 and 4M) perchloric acid as a chromatography solvent. Is a wash down fume hood still necessary for use in that context. I have typed out the procedure given to students below. 


Thanks for any insight you have.


Ion Exchange Separation of Chromium Complexes

Experimental procedure

Safety Note: Perchloric acid, HClO4, is a strong oxidant and can react explosively with some organic compounds such as acetone. In the present experiment, which is conducted entirely in aqueous solutions, there should be no hazard as long as the solutions are kept away from organic solvents. At the end of the experiment place all the solutions that contain chromium and perchloric acid into a labeled waste receptacle for them. The solutions should never be poured down the sink.

Preparation of Ion Exchange Column

A buret (about 10-mm inner diameter) may be conveniently used in this experiment. Fill the buret three-quarters full with distilled water. Push a small plug of cotton or glass wool to the bottom of the buret with a rod. With the stopcock on the buret open and a large beaker positioned under the tip of the buret, pour into the buret a slurry of Dowex 50W-X8 (50-100 mesh, H+ form) cation exchange resin in deionized water until a final resin height of approximately 15cm is achieved. Allow water to pass through the resin until the effluent is colorless (this should take less than 100ml). Then lower the water level so it coincides with the top of the resin, and close the stopcock. If the water level drops below the top of the resin, channels will develop. Because channeling reduces the separation efficiency of a resin, never allow the resin to dry.

Prepare 200ml each of 0.1, 1.0 and 4.0M solutions of HClO4. These solutions will be used to elute the desired complexes.

trans-Dichlorotetraaqupchromium (III) Ion, trans-CrCl2(OH2)4+

Prepare a 0.35M Cr(III) solution by dissolving 2.33 g (8.7mmol) of commercial CrCl3 6 H2O in a mixture of 25ml of H2O and one drop concentrated HClO4. Do no heat the solution to dissolve the solid. Important: Record the time of day when the dissolution of the CrCl3 6 H2O is performed. Portions of the Cr (III) solution will be used throughout the experiment.

Immediately after this 0.35M Cr(III) solution is prepared, add 5 ml of it to the cation exchange column previously prepared and drain until the solution and resin levels are the same. Elute with 0.1M HClO4. When the most intense portion of the broad green band begins to drip out of the buret, collect a 5-ml fraction and immediately record the spectrum of the fraction on a visible spectrophotometer in the wavelength range from 350 to 800 nm using glass cells of 1 cm path length.


Chloropentaaquochromium (III) Ion , CrCl(OH2)52+

When CrCl2(OH2)4+ is warmed briefly in aqueous solution, much of it is converted to the cation CrCl(OH2)52+. Place an Erlenmeyer flask containing 5 ml of the 0.35M Cr(III) solution in a boiling hot water bath for 3 mins. (Do not allow the solution inside the flask itself to come to a boil). After 3 min are up, remove the Erlenmeyer flask from the bath and immediately add 5ml of distilled water. Pour the entire solution into the same buret that was used above. Drain the solution to the resin level and flush the column with 0.1M HClO4 until the unreacted CrCl2(OH2)4 has been eluted. The desired complex, CrCl(OH2)52+ is then eluted with 1.0M HClO4. Collect 5 ml of the most intensely colored fraction that elutes. Measure the visible spectrum of the solution.


Hexaaquochromium (III) Ion, Cr(OH2)63+

Combine 5 ml of the 0.35 M Cr (III) solution with 5 ml of distilled water and boil for 5 min. Add all of this solution to the same buret and drain until the solution level reaches that of the resin. First rinse the column with 1.0M HClO4 to remove any unreacted CrCl2(OH2)4+  or CrCl(OH2)52+. Then elute the complex with 4.0 M HClO4. Collect 5 ml of the intensely colored portion of the eluted Cr(OH2)63+ solution and then record its visible spectrum.



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