Sørensen’s pH scale, named after Danish biochemist Søren Peter Lauritz Sørensen, is a widely used quantitative tool for measuring a solution’s acidity or alkalinity (basicity). It’s fundamental in chemistry, biology, and many other fields.

The Scale:

 Range: The pH scale runs from 0 to 14, with 7 being neutral.

 Interpretation:

     0-6: Acidic (increasing acidity as the number decreases)

     7: Neutral (equal concentration of hydrogen and hydroxyl ions)

     8-14: Alkaline (increasing basicity as the number increases)

 Logarithmic: Each unit difference on the scale represents a tenfold change in the concentration of hydrogen ions (H+). For example, a solution with a pH of 4 is 10 times more acidic than a solution with a pH of 5.

Mathematical Basis

The pH is calculated as the negative logarithm (base 10) of the hydrogen ion concentration:

pH = -log[H+]

This equation reflects that smaller H+ concentrations correspond to higher pH values, indicating less acidic solutions.

Applications

The pH scale has numerous applications across various domains:

 Chemistry: Understanding chemical reactions, predicting their behavior, and optimizing reaction conditions.

 Biology: Maintaining the proper pH balance in living organisms, essential for various physiological processes, including enzyme activity and protein structure.

 Environmental science: Monitoring water quality, assessing soil health, and studying the impact of pollutants on ecosystems.

 Medicine: Diagnosing various diseases, developing medications, and formulating cosmetics with optimal pH levels for skin and hair health.

 Food science: Controlling food spoilage, preserving food quality, and ensuring food safety.

Limitations and Considerations

 Temperature dependence: The pH value of a solution can slightly change with temperature.

 Ionic strength dependence: The pH scale considers the activity of hydrogen ions, not just their concentration, meaning the presence of other ions can influence the measured pH.

 Applicability: The pH scale primarily applies to aqueous solutions. Measuring the acidity of non-aqueous solutions often requires different methods.

Sørensen’s pH scale provides a valuable tool for understanding and quantifying the acidity/alkalinity of solutions. Its widespread use across various disciplines highlights its significance in numerous scientific and practical applications.