The pH is a chemical parameter of aqueous solutions; measures acidity or alkalinity by indicating the concentration of hydrogen ions, H + , in the solution. The pH is defined as the negative value of the logarithm of the concentration of hydrogen ions in the solution . The usual range of pH values is from 0 to 14, but if the molar concentration of hydrogen ions in an acid is greater than one, the logarithm value will be positive and the final pH value will be negative. But this is not something experimentally verifiable.
For example, the pH of an aqueous solution of hydrochloric acid of molar concentration equal to 12 is calculated as –log(12) = –1.08. This pH value cannot be measured experimentally. The instruments used in the laboratory to measure pH, such as papers that change color depending on the pH of the solution, do not provide for this case. And the tubes of the electronic pH meters do not measure negative values either. But the main thing to keep in mind is that strong acids, such as hydrochloric acid, do not completely dissociate at such high concentrations, so the actual pH will be higher than obtained from this calculation.
In conclusion, it is not possible to measure such a low pH and it is difficult to determine how much the pH decreases when the concentration of a strong acid increases when dealing with very concentrated solutions, since a complete dissociation of the acid is not induced, leaving the acid in solution. hydrogen ion. Similar reasoning can be applied to highly alkaline solutions, solutions with a pH greater than 14.
Fountain
Catherine E. Housecroft, AG Sharpe. Inorganic Chemistry . Pearson Education. Prentice Hall, 2001.
