Aqueous Ionic Equilibrium

In the strictly scientific sense of the word, insolubility does not exist, and even those substances characterized by the most obstinate resistance to the solvent action of water may properly be designated as extraordinarily difficult of solution, not as insoluble. 

3 Buffer Effectiveness Buffer Range and Buffer Capacity 765 

WE HAVE ALREADY seen the importance of aqueous solutions, first in Chapters 4, 

Every year, thousands of dogs and cats die from consuming a common household product antifreeze that was improperly stored or that leaked out of a car radiator. Most types of antifreeze used in cars are aqueous solutions of ethylene glycol  

Some brands of antifreeze nse propylene-glycol, which is less toxic than ethylene glycol. 

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Consider just a few cases of aqueous equilibria. The magnificent formations i n limestone caves and the vast expanses of oceanic coral reefs result from subtle shifts in carbonate solubility equilibria. Carbonates also influence soil pH and prevent acidification of lakes by acid rain. Equilibria involving carbon dioxide and phosphates help organisms maintain cellular pH within narrow limits. Equilibria involving clays in soils control the availability of ionic nutrients for plants. The principles of ionic equilibrium also govern how water is softened, how substances are purified by precipitation of unwanted ions, and even how the weak acids in wine and vinegar influence the delicate taste of a fine French sauce. In this chapter, we explore three aqueous ionic equilibrium systems acid-base buffers, slightly soluble salts, and complex ions. 

The final type of aqueous ionic equilibrium we consider involves a different kind of ion than we ve examined up to now. A simple ion, such as Na" " or S04 , consists of one or a few bound atoms, with an excess or deficit of electrons. A complex ion consists of a central metal ion covalently bonded to two or more anions or molecules, called ligands. Hydroxide, chloride, and cyanide ions are some ionic ligands water, carbon monoxide, and ammonia are some molecular ligands. In the complex ion Cr(NH3)6, for example, Cr is the central metal ion and six NH3 molecules are the ligands, giving an overall 3-1- charge (Figure 19.13). 

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