ABSTRACT
A neutral solution is one in which the concentrations of H+ ions and OH− ions are equal. At 25°C, this occurs at a pH of 7.0, but this is temperature dependent, a fact which is important when considering measurements made at different temperatures. Neutral pH is 7.4 at 4°C, but 6.8 at 37°C. The standard range over which pH is normally regarded to lie is between pH = 1 (a very acidic solution) where [H+] is 0.1 mol l−1 and pH = 14 (a very alkaline solution) where [H+] is 10−14 mol l−1. However, these are not physical limits and whilst pH values outside these limits are uncommon and probably nonexistent in living systems, in theory it is possible to exceed these values.
