Water as Both Acid and Base

Write an equation that shows a water molecule transferring a hydrogen ion to 

This reaction shows that both hydronium ion and hydroxide ion will be present in aU aqueous solutions. However, the equilibrium for the reaction lies on the reactant side and, consequently, the amount of hydronium ion present in pure water is very small, 1 x 10 moles per liter of water. The number of moles of hydroxide ion present in pure water is the same (1x10 moles per liter) because each transfer of a hydrogen ion from one water molecule to another produces one hydronium ion and one hydroxide ion. 

The concentrations of hydronium ion and hydroxide ion in aqueous solutions are so important that a special mathematical function is used to express them. The pH of a solution is defined as  

The brackets indicate the unit of solution concentration known as molarity. Molarity (M) is defined as the number of moles of a substance in one liter of solution. Notice that the symbol p simply stands for the negative logarithm to the base 10. 

In pure water the hydrogen ion concentration is 1 x 10 mole/liter and thus the pH is -log[l X 10 M] = 7. Although hydrogen ions in water are covalently attached to oxygen in the hydroninm ion, it is common to use the terms hydrogen ion and hydroninm ion interchangeably. 

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According to this definition NHj is regarded as an acid (NH4 NH3 + H ) and water as both acid and base, since... 

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