30.14
Tampone fosfato
Il sistema tampone fosfato è un meccanismo biologico fondamentale per mantenere la stabilità del pH nel corpo. Questo sistema funziona principalmente…
Il sistema tampone fosfato è vitale nelle urine e nel liquido intracellulare.
È costituito da sodio diidrogeno fosfato e sodio idrogeno fosfato.
Poiché il diidrogeno fosfato di sodio è un acido debole, non si dissocia molto in soluzioni acide e neutre.
Tuttavia, quando una base forte, come l'idrossido di sodio, viene introdotta nella soluzione, il sodio diidrogeno fosfato si dissocia per cedere ioni idrogeno. Questi ioni si legano agli ioni idrossido, formando molecole d'acqua.
Allo stesso tempo, si forma anche l'idrogeno fosfato di sodio.
Poiché questo processo converte l'idrossido di sodio nell'idrogeno fosfato di sodio a base debole, il pH della soluzione aumenta solo modestamente.
L'idrogeno fosfato di sodio non si dissocia in condizioni alcaline.
Ma, quando un acido forte come l'acido cloridrico viene aggiunto alla soluzione, il fosfato acido di sodio assorbe gli ioni idrogeno, formando il fosfato monobasico di sodio.
Poiché questo processo converte l'HCl nel fosfato monobasico acido debole, il pH della soluzione si riduce solo leggermente.
View the full transcript and gain access to JoVE Core videos
Q1: What are the two main components of the phosphate buffer system?
The phosphate buffer system consists of sodium dihydrogen phosphate (NaH2PO4), which acts as a weak acid, and sodium hydrogen phosphate (Na2HPO4), which serves as a weak base. These two components work together to neutralize both strong acids and strong bases, maintaining pH stability in urine and intracellular fluid.
Q2: How does the phosphate buffer respond when a strong base is added?
When a strong base like sodium hydroxide is introduced, sodium dihydrogen phosphate donates hydrogen ions that bind with hydroxide ions, forming water molecules. This converts the strong base into sodium hydrogen phosphate, a weak base, so the pH rises only modestly instead of dramatically.
Q3: What happens to the phosphate buffer when a strong acid is added?
When a strong acid like hydrochloric acid is added, sodium hydrogen phosphate accepts hydrogen ions and forms sodium dihydrogen phosphate. This converts the strong acid into a weak acid, causing only a slight pH reduction rather than a significant drop.
Q4: Why doesn't sodium dihydrogen phosphate dissociate in neutral or acidic solutions?
Sodium dihydrogen phosphate is a weak acid that does not fully dissociate under neutral or acidic conditions. It remains largely intact in these environments, but when exposed to strong bases, it readily donates hydrogen ions to neutralize the base and stabilize pH.
Q5: Where does the phosphate buffer system function in the body?
The phosphate buffer system is vital in urine and intracellular fluid, playing a critical role in renal physiology. It helps excrete hydrogen ions and stabilize urine pH, contributing to the body's overall acid-base balance through renal regulation of acid base balance.
Q6: What is the relationship between sodium hydrogen phosphate and strong acids?
Sodium hydrogen phosphate, the weak base component, neutralizes strong acids by accepting hydrogen ions released by the acid. This reaction binds excess hydrogen ions and converts the strong acid into sodium dihydrogen phosphate, a weak acid, preventing significant pH reduction.
Q7: How does the phosphate buffer system maintain pH stability?
The phosphate buffer system minimizes pH changes through its dual capacity to neutralize both strong acids and strong bases. By converting strong acids into weak acids and strong bases into weak bases, it effectively stabilizes the solution's pH even when significant amounts of acid or base are introduced.