Тема: Буферные растворы и буферные системы
По составу буферные растворы делятся
жүктеу/скачать 160.5 Kb.
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- Бұл бет үшін навигация:
- Например, карбонатный буфер
- Prt-COONa белок – соль
| По составу буферные растворы делятся на следующие типы:
Смесь слабой кислоты и её соли от сильного основания (щелочи). Например, ацетатный буфер Гидрокарбонатный (бикарбонатный) буфер 2. Смесь слабого основания и его соли от сильной кислоты. Например, аммонийный буфер 3. Смесь двух солей. Например, карбонатный буферФосфатный буфер 4. Белковые буферные системы, которые в общем виде можно представить как Prt-COOH т.е. белок – кислота Prt-COONa белок – сольВ белковые буферные системы входят белки плазмы, гемоглобин (Нb) и оксигемоглобин (НbО2) эритроцитов. Гемоглобиновый буфер оксигемоглобиновый буфер К белковым буферным системам относится водный раствор аминокислот (аминокислотный буфер), которые существуют в виде биполярных ионов R-CH-COOH ↔ R-CH-COO- | | NH2 NH3+ All these systems have the ability to soften the action of various factors that affect the pH of liquids. By the mechanism of action, buffer systems are divided into acidic, basic and ampholytic. Let us consider the mechanism of BUFFERING ACTION of acidic buffer systems. Acetate buffer: ↔ (1) Acetic acid CH3COOH weak electrolyte, α << 1. Sodium acetate СН3СООNа is a strong electrolyte α ≈1. The presence of СН3СООNа salt in the buffer mixture completely suppresses acid dissociation, because salt contains an ion common with acetic acid. If hydrochloric acid is added to this solution, i.e. introduce the H+ ion, then HCl will interact with the salt to form a weak acid CH3COOH (the salt component of the acetate buffer enters into interaction): + Н+ + Cl- → + Na+ + Cl- (2) From equation (2) it can be seen that the strong acid added to the buffer in solution is replaced by an equivalent amount of weak acid, its concentration increases and, according to the Ostwald dilution law, the degree of dissociation of acetic acid decreases. As a result, Сн+ and the pH of the solution (active acidity) will not change until all the buffer salt has completely reacted with the added acid. The total acidity of the solution increases with the addition of HCl acid. If alkali is added to the acid buffer, i.e. introduce an excess of OH- ions, then the alkali will interact with the acid (neutralization reaction), forming salt and water: + Na+ + OH- → + H2O (3) As a result of this reaction (3), the added alkali is replaced by an equivalent amount of salt, which, due to hydrolysis, has weakly basic properties, which affects the reaction of the medium to a much lesser extent than NaOH. OH- ions are bound by H+ ions into low-dissociated water and the active acidity of the pH mixture remains almost unchanged. However, instead of the reacted acid ions H+ and CH3COO- due to the dissociation of acetic acid, an insignificant amount of new ions H+ and CH3COO- is formed, but they practically do not change the active acidity of the buffer mixture. The total acidity of the buffer mixture decreases with the addition of alkali. The mechanism of action of salt buffer systems is acidic. In such buffer systems, acidic salt (NaHCO3, NaH2PO4) acts as a weak acid. Let's consider the mechanism of the buffering action of the ammonium buffer (the main mechanism of action). + Н+ + Cl- → + H2O (4) According to equation (4), the addition of small amounts of a strong acid to the ammonium buffer results in the formation of an equivalent amount of salt. The active acidity of the mixture pH practically does not change (there are small changes due to the formation of salt from a weak base, but they do not significantly affect the pH). The total acidity of the buffer mixture increases with the addition of acid. By adding small amounts of alkali to the ammonium buffer (reaction equation 5), an equivalent amount of a weak base is formed. The active acidity of the pH solution remains practically unchanged. The total acidity of the buffer solution decreases with the addition of alkali. + Na+ + OH- → + Na+ + Cl- (5) жүктеу/скачать 160.5 Kb. Достарыңызбен бөлісу:
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