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
Alkali–silica reaction mineral acid-base reaction between NaOH or KOH, calcium hydroxide, also known as Portlandite, or (Ca(OH)), and silicic acid (HSiO, or Si(OH)). When complete and to simplify, this reaction can be schematically represented as following: However, the ASR reaction significantly differs from the pozzolanic reaction by the fact that it is catalysed by soluble alkali hydroxides (NaOH / KOH) at very high pH. It can be represented as follows using the classical geochemical notation for fully hydrated dissolved silica (Si(OH) or silicic acid: HSiO), but an older industrial notation also exists (HSiO, hemihydrated silica (does not exist), by analogy with carbonic