1. It is calibrated against buffer solutions of known hydrogen ion activity . 2. For example, pH is defined as the negative logarithm of the hydrogen ion activity . 3. Debye and H�ckel developed a theory with which single ion activity coefficients could be calculated. 4. Single-ion activity coefficients can be calculated theoretically, for example by using the Debye H�ckel equation. 5. Expressions were derived for the variation of single-ion activity coefficients as a function of ionic strength. 6. This led to the development of what is now called the free-ion activity model ( FIAM ). 7. PH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity , " a" 8. Firstly, the cell is filled with a solution of known hydrogen ion activity and the emf, " E" 9. However, chemists have never been able to give up the idea of single ion activities , and by implication single ion activity coefficients. 10. However, chemists have never been able to give up the idea of single ion activities, and by implication single ion activity coefficients.
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