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Color Chemistry

One of the straightforward, cost effective, and “Best” accepted practices frequently used by EPA personnel for the detection and identification of hazardous materials is that of simple color change chemistry. Since a color change often accompanies a “chemical change” for determination, you might suspect a chemical reaction is at the root of this indicator. This is indeed the case, and solidly cements this method for sure identification, giving the Hazardous Materials responder confidence to then make life important operational decisions.  Since this basic concept gives us “best practices” decision making capabilities, a closer understanding of these principles is mandatory to deliver a “professional response.”

This month, featured pictures include “pictures from the field” at the recent winter 2014 Madonna University Hazardous Materials “Technician” course just completed this April. We used the ChemCat for the first class after our recent purchase. One of the features of this “kit” is color chemistry. This is used in many tests and provided an excellent identification process for the scenario “clandestine methamphetamine drug lab” that the students responded to for their final scenario.

As hazardous materials responders, we should be aware that color change chemistry is the addition of Hydrogen Ions (H) for determining Acidic properties while the subtraction of Hydrogen Ions and/or additions of Hydroxyl Ions (OH) being responsible for Alkaline (bases) properties. But exactly “how” does this happen on our color-metric strips?

In all organics and some synthetics, color and molecular structure ARE related. Light energy is delivered through little pouches called “photons.” Different “colors” of light pack different “amounts” of energy in their photon pouches. All materials absorb “some” energy. BUT, only substances that absorb photons of VISIBLE light will have COLOR. While molecules are very selective about which photons they will absorb, they are so characteristic that they can reliably be used as a “fingerprint” to identify that molecule in a mixture. Molecules have “set” or quantized energies which means they ONLY exist at certain allowed energy states. So, photons can only be absorbed if its energy is exactly the amount to take the molecule from one energy state to another.

Acids/Alkaline (Bases) is an excellent example for this technology. Since different molecules have different colors, this means molecular structure has something to do with the SIZE of these energy transitions associated with the absorption of visible light. While a lot of other factors are involved in this, one general principle should be understood. Color changes are caused by electron “confinement” within the different molecular structures. Therefore, “more” confinement in a molecular structure shows the light absorbed as “blue”, while less confinement in a molecular structure shows the light absorbed as “red.”

Since our eye sees the opposite of what was absorbed, when we see red, blue was absorbed, and vice versa. So, the molecular structure of an unknown substance that absorbs blue, allows us to “see” a red color, on an indicator paper, telling us the substance is acidic in nature. The reverse is also true.

The color of a hazardous liquid that “IS” identified may be helpful as a secondary confirmation in identification of the substance. The color of a transparent substance is due to the absorption of photon energy (in pigment/color) and what resulting color we are able to “see” passing through the material. This “MAY” be helpful as a secondary identifier for some particular substances as confirmed by the manufacturer of the substance released.

A glass of red wine when held up to the light allows you to “see” the color red because the substances molecular structure has “absorbed” all of the remaining colors and only allows “RED” to pass through the liquid. These procedures are directly translated onto indicator paper or “strips” allowing responders to “READ” the color passed through, or not absorbed by the structure. The color indicator we “see” affords us decision making for our operations at a hazardous material incident.

Plant “pigments” or color, can act as acid/alkaline (base) indicators in much the same way. Plants, flowers etc, that have the same color, contain the exact same molecular structure portion that interprets colors/photon absorption comparable to the same like structure found in chemical liquids. While it is amazing that totally different plants contain the exact same “color change” structure, this explains like colors. Color change in the fall and spring are examples of plant molecular structure changes due to maturity, temperature, sunlight amount variance, and additional Environmental factors we refer to as the “seasons.” Tampering with the genes in flowers has directly given us the variance of colors that now exist.

While this “best practices” of color chemistry can determine many more essential properties other than Acid/Alkaline (Base) information, most of these exact compounds and indicators are proprietary in nature to preserve the manufacturer’s product and marketability. Oxidizers, Halogens, Nerve Agents, Bio-Agents, and other Hazardous Materials can be confidently evaluated using color chemistry to make operational decisions at Hazardous Materials Incidents.

                                            Haz Mat Mike





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