University:
Liberty University
Course:
BIOM 500 | Introduction to Biomedical Sciences
Academic year:

2024
Views:

57

Pages:

6
Author:

Sheha A.

**The Concept of pH** * The term pH is defined as the "negative log of the hydrogen ion concentration". i.e. pH = -log[H+] * The value of [H+] of pure water at 25°C is 1.0 x 10^-7. The pH can be calculated as follows: pH = -log[H+] = -log(10^-7) = -(-7) = 7.0 * The pH value of 7 is said to be neutral pH. * Solutions having a pH greater than 7 are basic. (The concentration of OH- is greater than the concentration of H+ ions). * Solutions having a pH less than 7 are acidic. **Acids and Bases** * Acids are defined as proton donors (proton donors). * Strong acids (e.g., HCl, H₂SO₄) dissociate completely in an aqueous solution. * Weak acids (e.g., acetic acid) dissociate only partially in an aqueous solution. * Strong bases (e.g., KOH, NaOH) dissociate completely in an aqueous solution. * Weak bases (e.g., Ca(OH)₂) dissociate partially in an aqueous solution. * Many biologically important molecules, including amino acids, can act as both acids and bases. **Measurement of pH and Indicator** * The pH of an aqueous solution can be approximately measured using acid-base indicators like litmus, phenolphthalein, and methyl orange. * These indicators change color at specific pH ranges, indicating the acidity or basicity of the solution. * The precise measurement of pH is done using a pH meter, which is a device with a glass electrode that is sensitive to hydrogen ions. **pH of an Aqueous Solution** Solution | Color of litmus paper | Color of phenolphthalein | pH range | Nature ---| --- | --- | --- Acidic | Red | Colorless | Less than 7 | Acidic Basic | Blue | Pink | Greater than 7 | Basic Neutral | Red/Blue | Colorless | Approximately 7 | Neutral **Acid-Base Balance** * The overall acid-base balance of the body is maintained by controlling the H+ concentration of the body fluids. * The normal pH of systemic arterial blood is 7.35-7.45. * Homeostasis of pH is maintained by buffers, respiration (via exhalation of CO2), and excretion of H+ ions and reabsorption of HCO3- via the kidneys. * Any significant change in pH can have serious consequences on biological molecules and processes. * The pH of blood plasma below the normal value of 7.4 is called acidosis. * The pH of blood plasma above the normal value of 7.4 is called alkalosis. * The maintenance of blood pH is crucial for the proper functioning of various physiological processes.