pH indicator

The negative logarithm of hydrogen ion concentration is denoted as pH and is called the hydrogen indicator:

pH = -lg[H⁺]; pH + pOH = 14.

In an acidic aqueous solution, the hydrogen ion concentration can vary from 1 to 10^–7, hydroxide ions from 10^–7 to 10^–14, pH from 0 to 7, pOH from 7 to 14. However, the values of K_w and pH + pOH remain constant. The pH of acidic solutions is <7, alkaline solutions have a pH >7, neutral pH = pOH = 7. The dissociation of water is an endothermic process, therefore, as the temperature increases, K_w increases and pH decreases. The pH hydrogen indicator is often used in biochemical research as well as in clinical practice to describe the acidic-basic properties of biological environments and pharmaceutical substances. The blood pH under normal conditions fluctuates between 7.25 and 7.44. At a temperature of 37 °C, a neutral environment corresponds to pH = 6.8, making blood weakly alkaline. The optimal pH for enzymes varies greatly, for example, the enzyme pepsin in gastric juice functions at pH 1.5-2.0, while blood catalase at pH 7. The lower the pH, the more acidic the solution.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė