Basic Remarks on Acidity

This Review provides a unified view on Brønsted acidity. For this purpose, a brief overview of the concepts acidity, acid strengths, and pH value is given, including problems, proposed solutions, and the use of the pH abs / scale as a unifying concept. Thereafter, some examples of the accessibility and application of unified pH abs values are given. The Review is rounded off with the analogy of acid‐base chemistry to redox chemistry with the introduction of the unified redox scale pe abs . The combination of pH abs and pe abs values in the protoelectric potential map (PPM), as elaborated in ongoing studies on the thermochemistry of single ions, provides a means to classify and to compare all possible acid‐base/redox reactions in a medium‐independent and, thus, unified fashion.