Acids and Bases The pH of Solutions

With very few exceptions, naturaiiy occurring acids and aikaiies are weak. Aii acids known in antiquity were of organic origin some occur in fruits, especiaiiy in unripe fruitjuices. Most ancient aikaiies were derived from the ash of piants such as bariiia, Salsola soda and Salsola kali (Russian thistie), and keip. 

Aii acid solutions taste sour and are more or iess corrosive and chemicaiiy quite reactive they react with most metais, many of which are corroded and dissoived by acids. Alkaline solutions, aiso chemicaiiy reactive, are caustic (they burn or corrode organic tissues), taste bitter, and feei siippery to the touch. Both acids and bases change the coior of indicators (substances that change coior, hue, or shade depending on whether they are in an acid or basic environment). 

When an acid soiution is mixed with an aikaiine soiution in the appropriate quantities, the two soiutions are said to neutraiize each other the hydrogen (H ) cations of the acid and the hydroxyl (OH ) anions of the base combine to form water molecules (HOH or H2O), canceling the (acid or alkaline) properties of the other. The term neutralization is used to refer to this reaction because the acid and basic properties of the two solutions are neutralized and the solution is neutral, neither acid nor basic  

Neutral solutions also contain a dissolved salt, derived from the neutralization of the acid and the base (a salt is an ionic compound formed in a neutralization reaction and is composed of the cation of an alkali and the anion of an acid). When a solution of carbonic acid (formed when atmospheric carbon dioxide dissolves in water), for example, reacts with an alkaline solution of lime, the two solutions neutralize each other and form a salt, calcium carbonate  

The acidity and alkalinity of water solutions and, therefore, differences in their acidity or alkalinity, can be quantified and assigned numerical values. One way of doing this is to express the concentration of hydrogen ions in solutions on a numerical scale. Such a scale is provided by the widely accepted pH scale, in which the strength or weakness of acid or alkaline 

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