PH of neutrality is not exactly 7 (25 °C), although this is a good approximation in most cases. Neutrality is defined as the condition where [H] = [OH] (or the activities are equal). Since self-ionization of water holds the product of these concentration [H]×[OH] = K, it can be seen that at neutrality [H] = [OH] = , or pH = pK/2. pK is approximately 14 but depends on ionic strength and temperature, and so the pH of neutrality does also. Pure water and a solution of NaCl in pure water are both neutral, since dissociation of water produces equal numbers
PH the concentration of the acid, so [A] = [H]. After some further algebraic manipulation an equation in the hydrogen ion concentration may be obtained. Solution of this quadratic equation gives the hydrogen ion concentration and hence p[H] or, more loosely, pH. This procedure is illustrated in an ICE table which can also be used to calculate the pH when some additional (strong) acid or alkaline has been added to the system, that is, when C ≠ C. For example, what is the pH of a 0.01M solution of benzoic acid, pK = 4.19? For alkaline solutions an additional term is