Hazard Categories and Chemistry Principles

The testing of chemicals/wastes to establish the nature of their hazard capacity/threat in accordance with regulatory requirements, falls into four categories (1) reactivity, (2) ignitability/flammability, (3) corrosivity, and (4) EP toxicity. Commercial chemical products, specific wastes, and wastes from specific processes may be listed as hazardous wastes because they are known to present toxic hazards in the maimer of the tests above and/or are known to present serious toxic hazards to mammals/humans. In the discussion to follow, various chemical groups will be examined primarily in the context of reactivity, ignitability, and corrosivity. 

The EPA defines corrosivity in tenns of pH (i.e., wastes with pH 2 or 2.5) or in terms of ability to corrode steel (SAE 20) at a rate of 6.35 mm (0.250 in.) per year at a temperature of 55°C (13°F). This discussion will address corrosivity as it applies to acids and caustics. Acids are compounds that yield H+ions (actually H30+ ions) when dissolved in water. Common industrial acids include acetic, nitric, hydrochloric, and sulfuric, acids. The terms concentrated and dilute refer to tire concentrations in solution. Mixing a concentrated acid with enough water will produce a dilute acid. For example, a bottle of concentrated HC1 direct from die manufacturer is approximately 12N in HC1, while a solution of HC1 used in a titration may be only 0.5N. The latter is a dilute acid solution. 

Strong and weak acids are classified by how completely they ionize in solution. For example, HC1 is classified as a strong acid because it is completely ionized to H+ and Cl ions. Acetic acid is classified as a weak acid because it does not totally ionize in solution. As mentioned earlier, weak acids such as acetic acid have higher pKas. The pKa for acetic acid is 4.75. The negative antilog of this value (1.76 x 10 5) can be used to calculate the concentrations at equilibrium of the acetate and hydrogen ions. Strong acids include perchloric, hydrochloric, sulfuric, nitric, and hydriodic 

Fire and Explosion Hazards Handbook of Industrial Chemicals 

The acidic nature of a given solution is characterized by its pH, where pH is the negative logarithm of the molar H+ concentration (-log (H+]). A solution with pH 7 is acid, a solution with pH 7 is neutral, and a solution with pH 7 is basic. For example, the pH of lemon juice is 2, while the pH of lye is about 14. 

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