Hydrofluoric Acid: A Weak Acid – Yet It Dissolves Glass?

On the far right side of the Periodic Table of the Elements is listed the halogens, which include fluorine, chlorine, bromine, iodine, and astatine. In order of ascending atomic weight we have: fluorine and chlorine gases, bromine liquid, and iodine and astatine solids. Each exhibits a –1 valence. Each attaches to a single atom of hydrogen to form an anhydrous acid. Most of these acids are considered very strong with the exception of hydrofluoric acid. It is comparably a relatively weak acid. This is the case, even though hydrofluoric is the only acid stored in polyethylene bottles because it dissolves glass. Since it can eat its way through glass, how can hydrofluoric acid be considered a weak acid? Hydrofluoric Acid Attacks Glass While hydrofluoric acid is usually written HF, for…
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Fly Ash for Concrete: Lowers Cost, Rids Waste and Aids the Environment

Chemistry, Technology
[caption id="attachment_15873" align="alignright" width="440"] Finding uses for waste products - Fly Ash[/caption] Fly ash for concrete? Most concrete is formulated from water, broken stone or gravel, sand, and cement—generally Portland cement. The formulation can include a small quantity of waste material. Fly ash is one such waste material. It offers three advantages. It reduces the need to dispose of some of earth’s abundant fly ash waste, it decreases cost, and decreases helps decrease damage to the environment. What is Fly Ash? Fly ash is the lightweight particulate carried along by flue gases produced from burning coal in boilers. It may be removed electrostatic precipitation. Although coal is mostly carbon, coal deposits are embedded in rock. Thus, inevitably, burning coal yields some silica (SiO2), alumina (Al₂2O3), and calcium oxide (CaO). Tragically,…
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Why Sand Filtration to Treat Waste Water?

[caption id="attachment_5157" align="alignright" width="440"] Treatment Plant - CCA SA 3.0 Germany by Martina Nolte[/caption] Is sand filtration out of date? If not, what are its advantages? Waste water received by a treatment plant must be processed several ways before it is sent to the sand filter, disinfected and discharged to the environment. Large objects and grit are first removed. Treatment to remove nitrogen and phosphorous follows.  Suspended solids are digested and removed. The waste water is next aerated, allowed to settle and then pumped to the sand filter. Sand filtration blocks tiny particles. A separate layer of activated carbon may be included in the sand filter. Sand Filtration Operation Particle removal features two mechanisms. Particles larger than the gaps between grains of sand are blocked. Many smaller particles are absorbed…
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