Hydroxide ions from autoionization

A substance is said to be amphoteric if it can behave either as an acid or as a base. Water is the most common amphoteric substance. We see this behavior in the autoionization of water, which involves the transfer of a proton from one water molecule to another to produce a hydroxide ion and a hy-dronium ion ... 

The OH contribution from the autoionization of water is negligible here, as was the contribution of HaO from autoionization in the 0.10 M HCl and HCIO4 solutions. When only a very small amount of strong acid or base is added to pure water (for example, 10 mol L ), we have to include the autoionization of water to describe the concentration of hydronium and hydroxide ions accurately. 

Although pure water is virtually 100% molecular, a small number of water molecules do ionize. This process occurs by the transfer of a proton from one water molecule to another, producing a hydronium ion and a hydroxide ion. This process is the autoionization, or self-ionization, of water. 

According to our equilibrium table, x = [OH ]. In this case, the autoionization of water makes a significant contribution to the hydroxide ion concentration so the total concentration will be the sum of 1.2 X 10A/ (from the ionization of F ) and 1.0 X 10 M (from the autoionization of water). Therefore, we calculate the pOH first as... 

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