30.14
Tampon phosphate
Le système tampon phosphate est un mécanisme biologique essentiel pour maintenir la stabilité du pH dans le corps. Ce système fonctionne principalemen…
Le système tampon phosphate est vital dans l’urine et les fluides intracellulaires.
Il se compose de dihydrogénophosphate de sodium et d’hydrogénophosphate de sodium.
Le dihydrogénophosphate de sodium étant un acide faible, il ne se dissocie pas beaucoup dans les solutions acides et neutres.
Cependant, lorsqu’une base forte, telle que l’hydroxyde de sodium, est introduite dans la solution, le dihydrogénophosphate de sodium se dissocie pour céder les ions hydrogène. Ces ions se lient aux ions hydroxyde, formant des molécules d’eau.
Dans le même temps, l’hydrogénophosphate de sodium se forme également.
Étant donné que ce processus convertit l’hydroxyde de sodium en hydrogénophosphate de sodium à base faible, le pH de la solution n’augmente que modestement.
L’hydrogénophosphate de sodium ne se dissocie pas dans des conditions alcalines.
Mais, lorsqu’un acide fort comme l’acide chlorhydrique est ajouté à la solution, l’hydrogénophosphate de sodium absorbe les ions hydrogène, formant du dihydrogénophosphate de sodium.
Étant donné que ce processus convertit le HCl en dihydrogénophosphate de sodium faible, le pH de la solution n’est que légèrement réduit.
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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.