Buffer solutions: preparation and use

Buffer solutions are solutions containing buffer systems. Buffer systems are mixtures containing a certain quantitative ratio of weak acids and their salts with strong bases or weak bases and their salts with strong acids. Such solutions have a stable concentration of H + ions when diluted with a neutral solvent (water) and add a certain amount of strong acids or bases to them.

Buffer solutions are found in the waters of the world's oceans, soil solutions and living organisms. These systems perform the functions of regulators that support the 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 can be acetate buffer system, the second - ammonium. There are natural and artificial buffer solutions. A natural buffer solution is blood containing hydrocarbonate, phosphate, protein, hemoglobin and acid buffer systems. An artificial buffer solution can be an acetate buffer consisting of CH3COOH.

Features of the internal composition and mechanism of the buffer systems will be considered using the acetate buffer system as an example: acetate acid / sodium acetate. In the aqueous medium, the components of the buffer system undergo electrolytic dissociation. Sodium acetate as a salt of a weak acid and strong base dissociates completely into ions. The presence of anions in such a buffer mixture depends on the concentration of the 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 the acid salt in it.

Thus, the concentration of H + ions in the main buffer is directly proportional to the concentration of the salt in it and inversely proportional to the concentration of the base.

In laboratory practice, buffer solutions with known pH values are used. Thus, 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 ratios of the components, buffer solutions with a given pH value are produced. Some are interested in how the solution is prepared.

For example, it is necessary to prepare an acetate buffer with several pH values. Initially, prepare 5M solutions of acetate and sodium acetate. To prepare the first solution, take 50 ml of each of the components. Guided by the formula, the concentration of H + ions in the resulting solution is determined.

For the next buffer solution, take 80 ml of the acid solution and 20 ml of the salt solution prepared earlier. There are a number of prescriptions for various buffer solutions used in chemical analysis and laboratory practice.

For buffer solutions, some properties are characteristic. These include, first of all, buffering - the ability to maintain the constancy of the concentration of H + ions when adding a certain amount of strong acid or strong base to the buffer solution. For example, if a small amount of chloride acid is added to the acetate buffer, the pH will not shift to the acid side, since the chloride acid will react with the exchange salt with a weak acid salt. As a result of the reaction, a strong acid, capable of shifting the pH to the acid side, is replaced by a weak acid and a neutral salt. The degree of dissociation of a solution of a weak electrolyte with increasing its concentration decreases, tends to zero, and the pH shift does not occur.