This article is semi-protected until February 3, 2020. Contrary to popular belief, the pH value can be less than 0 or greater than 14 for very strong acids and bases ph chart for r12 pdf. H is established by international agreement.
H in 1924 to accommodate definitions and measurements in terms of electrochemical cells. 17 g of hydroxide ions. Note that pH depends on temperature. C the pH of pure water is 7. It follows that electrode potential is proportional to pH when pH is defined in terms of activity. The difference between the two measured emf values is proportional to pH.
This method of calibration avoids the need to know the standard electrode potential. A combined glass electrode has an in-built reference electrode. Two or more buffer solutions are used in order to accommodate the fact that the “slope” may differ slightly from ideal. The reading from a second standard buffer solution is then adjusted, using the “slope” control, to be equal to the pH for that solution. When more than two buffer solutions are used the electrode is calibrated by fitting observed pH values to a straight line with respect to standard buffer values. C and a correction factor to be applied for other temperatures.