Buffer solutions are solutions containing buffer systems. Buffer systems are called mixtures, in the composition of which weak acids and their salts with strong bases or weak bases and their salts with strong acids are contained in a certain quantitative ratio . Such solutions have a stable concentration of H + ions when diluted with a neutral solvent (water) and a certain amount of strong acids or bases are added to them.
Buffer solutions are found in the waters of the oceans, soil solutions and living organisms. These systems perform the functions of regulators that support an active reaction of the medium at a certain value necessary for the successful course of metabolic reactions. Buffer solutions are classified into acidic and basic. An example of the former is the acetate buffer system, and the latter is ammonium. Distinguish between natural and artificial buffer solutions. A natural buffer solution is blood containing bicarbonate, phosphate, protein, hemoglobin and acid buffer systems. The artificial buffer solution may be an acetate buffer consisting of CH3COOH.
We will consider the features of the internal composition and mechanism of action of buffer systems using the example of the acetate buffer system: acetate acid / sodium acetate . In an aqueous medium, the components of the buffer system undergo electrolytic dissociation. Sodium acetate as a salt of a weak acid and a strong base completely dissociates into ions. The presence of anions in such a buffer mixture depends on the concentration of salt in it and the degree of its dissociation. The concentration of H + ions in the buffer system is directly proportional to the concentration of acid in it and inversely proportional to the content of this acid salt in it.
Thus, the concentration of H + ions in the main buffer is directly proportional to the concentration of salt in it and inversely proportional to the concentration of the base.
In laboratory practice, use buffer solutions with previously known pH values. So, the preparation of buffer solutions is carried out using solutions of a weak acid and its salt with a strong base or a weak base and its salt with a strong acid. Then, changing the quantitative proportions of the components, buffer solutions with a given pH value are prepared. Some are interested in how the solution is prepared.
For example, it is necessary to prepare an acetate buffer with several pH values. First, 5M solutions of acetate acid and sodium acetate are prepared. To prepare the first solution, 50 ml of each component is taken. Guided by the formula, determine the concentration of H + ions in the resulting solution.
For the next buffer solution, 80 ml of the acid solution and 20 ml of the salt solution prepared previously are taken. There are a number of prescriptions of various buffer solutions used in chemical analysis and laboratory practice.
Buffer solutions are characterized by some properties. These primarily include buffering - the ability to maintain a constant concentration of H + ions when a certain amount of strong acid or strong base is added to the buffer solution. For example, if a small amount of perchloric acid is added to the acetate buffer, a pH shift to the acid side will not occur, since perchloric acid will enter into a metabolic decomposition reaction with a weak acid salt. As a result of the reaction, a strong acid capable of shifting the pH to the acidic side is replaced by a weak acid and a neutral salt. The degree of dissociation of a solution of a weak electrolyte decreases with an increase in its concentration, tends to zero, and a pH shift does not occur.