Dissolution Characteristics of Phosphoric Acid

10 mol. Such a solution is called neutral . Thus, the ionization constant of water is defined by 

The angle brackets in Eq. 4.15 represent molar concentrations of the particular species. In practice, one may select 1 mol of water for study, which means (H2O) = 1 in Eq. 4.5. Eurthermore, it is customary to represent the negative logarithm to base 10 of the molar concentrations in Eq. 4.5  

When (H ) = ((OH) ), the solution is neutral water, and — log(H ) = — log((OH) ) = 7. If more H remains in the water, then it is acidic (pH 7), while more hydroxyl ions remain, then the solution pH will be higher than 7. 

Similar to dissociation of water, all soluble acid phosphates, and soluble oxides dissociate or dissolve in water. When acid phosphates dissociate in water, they lower the pH of the solution by releasing protons (H ), while most of the oxides or hydroxides when mixed with water release hydroxyl ions (OH ) by removing protons from the solution. As a result, initially neutral water becomes richer in protons when acid phosphates are dissolved in it and the pH becomes 7. On the other hand, for certain oxides such as those of alkaline elements (e.g., Na, K, Mg, and Ca), the pH is increased because the solution becomes deficient in protons. Thus, the pH scale is a good indicator of the extent of release of protons and hydroxyl ions and will be used throughout this book to represent the extent of acid-base reactions. 

For example, consider phosphoric acid, which when mixed in water, loses hydrogen and forms protons (H ) and anions (H2PO4, HPO , and PO ) of phosphates. The number of protons lost during the dissolution depends on the pH in which this dissociation takes place. These dissociation reactions are represented by the following equations  

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