30.14
Phosphatpuffer
Das Phosphatpuffersystem ist ein wichtiger biologischer Mechanismus zur Aufrechterhaltung der pH-Stabilität im Körper. Dieses System funktioniert haup…
Das Phosphatpuffersystem ist im Urin und in der intrazellulären Flüssigkeit lebenswichtig.
Es besteht aus Natriumdihydrogenphosphat und Natriumhydrogenphosphat.
Da Natriumdihydrogenphosphat eine schwache Säure ist, dissoziiert es in sauren und neutralen Lösungen nicht viel.
Wenn jedoch eine starke Base, wie z. B. Natriumhydroxid, in die Lösung eingebracht wird, dissoziiert Natriumdihydrogenphosphat und gibt Wasserstoffionen ab. Diese Ionen binden sich an Hydroxid-Ionen und bilden Wassermoleküle.
Gleichzeitig wird auch Natriumhydrogenphosphat gebildet.
Da bei diesem Prozess Natronlauge in die schwache Base Natriumhydrogenphosphat umgewandelt wird, steigt der pH-Wert der Lösung nur geringfügig an.
Natriumhydrogenphosphat dissoziiert unter alkalischen Bedingungen nicht.
Wenn jedoch eine starke Säure wie Salzsäure zur Lösung hinzugefügt wird, nimmt Natriumhydrogenphosphat die Wasserstoffionen auf und bildet Natriumdihydrogenphosphat.
Da bei diesem Prozess HCl in die schwache Säure Natriumdihydrogenphosphat umgewandelt wird, wird der pH-Wert der Lösung nur geringfügig gesenkt.
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.