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Solubility is another term associated with mixing two or more compounds together. The definition of solubility from the Condensed Chemical Dictionary is "the ability or tendency of one substance to blend uniformly with another, e.g., solid in liquid, liquid in liquid, gas in liquid, and gas in gas." The solubility may have varying degrees from one substance to another.
When researching chemicals in reference sources, relative solubility terms may include very soluble, slightly soluble, moderately soluble and insoluble. Generally, nothing is absolutely insoluble. Insoluble actually means "very sparingly soluble"; that is, only trace amounts dissolve.
Compounds of the alkali metals of family one on the Periodic Table are all soluble. Salts containing the ammonium ion (NH4), nitrates (NO3), perchlorates (ClO4), chlorates (ClO3), and organic peroxides containing carbon, hydrogen and two oxygen's bonded together are also soluble. All binary salt chlorides (Cl-), bromides (Br-) and iodides (I-) are soluble, except those containing silver (Ag), lead (Pb2) and mercury (Hg2). All sulfates are soluble except for those with the metals lead (Pb2), calcium (Ca2) strontium (Sr2), mercury (Hg2) and barium (Ba2). All hydroxides (OH) and metal oxides (containing O) are insoluble, except those of family one on the Periodic Table and Ca2, Sr2 and Ba2. All compounds that contain phosphate (PO4) carbonate (CO3), sulfate (SO3) and sulfur (S) are insoluble, except for those containing metals in family one on the Periodic Table and the ammonium ion (NH4). Most hydrocarbon compounds are mixtures and are not soluble, such as gasoline, diesel fuel and fuel oil.
Photo by Robert Burke
Molten sulfur is an element that presents inhalation and thermal hazards.
Compounds that are polar such as the alcohols, ketones, aldehydes, esters and organic acids are soluble in water, because water is also a polar compound. This concept is important to understand when selecting firefighting foams. Foam when applied to a flammable liquid is largely water. Polar liquids will take the water from the foam and the foam blanket will break down. Therefore, fighting fires involving polar liquids will require alcohol type or polar solvent foams.
There are some factors that effect the solubility of a material. One is particle size. The smaller the particle, the more surface area that is exposed to the solvent; therefore, more dissolving takes place over a shorter period of time. Higher temperatures usually increase the rate of dissolving. The term miscibility is often used synonymously with the term solubility. If a compound, for example, is miscible in water, it is water soluble. If it is immiscible, then it is insoluble in water.
Acetylene gas is produced when calcium carbide, a salt, is mixed with water. Acetylene gas is very flammable and unstable. When placed in a container, acetylene gas is dissolved in acetone to stabilize it. Many inorganic acids are made when a gas is dissolved in water to form the liquid acid. Anhydrous ammonia is very soluble in water. Vapor clouds of anhydrous ammonia can be knocked down with fog patterns, dissolving the ammonia in water and forming ammonium hydroxide.
Robert Burke will present "Hazardous Materials: Responding To Chemical & Biological Terrorism" at Firehouse Emergency Services Expo '97 in Baltimore July 24-27.
Robert Burke, a Firehouse® contributing editor, is a Fire Protection Specialist with the University of Maryland at Baltimore. He is a certified Hazardous Materials Specialist and has served on state and county hazardous materials response teams. Burke is a member of the Earleigh Heights, MD, Volunteer Fire Company and has 16 years' experience in career and volunteer fire departments, attaining the rank of assistant chief, as well as serving as a deputy state fire marshal. He holds a bachelor's degree in fire science and is an adjunct instructor at the National Fire Academy, Maryland Fire and Rescue Institute and Delaware County, PA, Fire Academy. Burke's book, Hazardous Materials Chemistry For Emergency Responders, was published in January 1997. He can be reached on the Internet at firstname.lastname@example.org, Part 1 of this report was published in May 1997.