CIRI Consultant Services why oils and grease effectively dissolve in other dry cleaning agents. Carbon tetrachloride dissolves benzene but should never be used when cleaning indoors because it is carcinogenic. tive charged sodium ion is surrounded by water molecules. Their negative ends are directed at the sodium and a negatively charged chloride ion surrounded by water molecules. Their positive ends are directed at the chloride. The ions comprising table salt are in cages of water molecules. When water molecules surround an ion that way the ion is hydrated. The cage of water molecules surrounding an ion neutralizes or insulates its charge. It also keeps the solutionʼs oppositely charged ions from attracting each other over distances. In the case of water, Na+ and Cl-cannot form a salt crystal. In contrast, non-polar molecular solu-tions cannot dissolve ionic solids, such as salt, since solids cannot be separated by positive and negative charged forces. They also cannot insulate the solidʼs ions from each other. When ionic solids are in non-polar molec-ular solutions they quickly attract each other and separate from the solution as solids. They congregate rather than dissolve. The result is an important fact of cleaning chemistry. Substances similar in molecular attrac-tion forces generally are soluble in one another. Polar solvents, such as water, dissolve ionic substances, like salt. Solvents comprised of non-polar mole-cules dissolve non-polar substances. Chemistry explains many cleaning mech-anisms. Soap is made when animal fats react with water and a strong base, like lye or caustic soda. When the base and the acidsʼ fats react an ion is released that has a negatively charged head connected to a long hydro-carbon chain. Typically, soap has a negatively charged carbon dioxide unit. This head connects to a long hydrocar-bon tail resembling those in oil, gasoline, grease and animal fat. The soap ionʼs hydrocarbon tail is not water soluble. It will, however, dissolve in like hydrocar-bons, such as grease and animal fat. Hydrophobic substances arenʼt water soluble either. In solutions containing soap the hydrophobic hydrocarbon tails of fatty acid ions interlace forming an oil-like glob. Meanwhile, the ionʼs charged head points toward the surrounding water molecules. This charged head has an affection for water. Fatty acid ions called micelles are formed by this love-fear relationship with water. Soap decomposes and removes oils and fats in fabrics and surfaces because “like dissolves like.” The soap ionsʼ hydrocarbon tails dissolve in the hydrocarbons being removed. That hydrocarbon substance is overlaid by the soap ionsʼ hydrocarbon tails. Gradually it separates as the charged, water-loving ion head is drawn toward sur-rounding water molecules. The attraction forces of the water mole-cules and the head of the long hydrocarbon chain pull the glob apart. As the breakdown occurs, the soap solu-tion holds bits of unwanted substance in colloidal suspension. The heads of the soap ions are the same charge and repulse each other. This prevents the substance being dis-solved from reforming. The suspended substance is emulsified and carried away in wash water. Synthetic detergents act like soap by breaking apart and dissolving the same substances. Instead of animal fat, however, they con-sist of man-made chemicals, such as sodi-um alkylbenzenesulfonates. Detergentsʼ main advantage is they work better than soap in hard water, the common state of ground water in urban and rural environments. The electrostatic states in detergents vary more than in soaps. Detergent ions have positive heads called cations or negative heads called anions. Other detergents are non-ionic or polar compounds with positive and negative ends. A synthetic detergentʼs anions donʼt become solids in hard water like in soap. Consequently, hard water does not affect their cleaning action. CM Are There Varying Degrees Of Solubility In Cleaning Chemistry? Consider what happens when a solid dis-solves in a liquid. A solidʼs molecules are arranged in a reg-ular pattern to maximize attraction forces. For the solid to dissolve, the dissolving solutionʼs molecular forces must overcome those forces holding the solid together. Sugar consists of molecules held tightly together by hydrogen bonding. It will not dissolve in gasoline. The gasolineʼs carbon-based molecular forces are too weak to overcome the sugarʼs hydrogen-based molecules. The sugar, however, dissolves in water because of its hydrogen-based molecules. It has one oxygen and two hydrogen atoms and attraction forces equivalent to sugar molecules. When sugar and water combine their molecules become interchangeable. Water alone dissolves many water-solu-ble substances, such as solids containing positive and negative ions. Ions are positively or negatively charged particles. Sometimes they are called ionic crystals. Salt — or sodium chloride — is one. When ionic substances dissolve in water the adjoining ions in the solid separate and are surrounded by water molecules. Water molecules are two positive charged hydrogen atoms joined by a single oxygen atom. The water molecule is called a polar mol-ecule meaning opposing molecule ends carry opposite electrical charges. Not all molecules are polar. Water is, however, because of its positive and negative ends. The electrostatic attraction of opposite charges holds the water molecules togeth-er to form water bodies. Its molecular polarity makes it particular-ly useful in cleaning because of its dissolvability. Salt also dissolves in water when a posi-24 CM/Cleaning & Maintenance Management ® • May 2009
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