30.14
磷酸盐缓冲系统
磷酸盐缓冲系统是维持体内 pH 值稳定性的关键生物机制。该系统主要通过两种成分运作：磷酸二氢钠 (NaH_2PO_4)，其充当弱酸，磷酸氢钠 (Na_2HPO_4)，其充当弱碱。
磷酸二氢钠在中性或酸性溶液中不会完全解离。当强碱，例如氢氧化钠 (NaOH)被引入溶液中时，磷酸二氢钠会贡献质子 (H^…
磷酸盐缓冲系统在尿液和细胞内液中至关重要。
它由磷酸二氢钠和磷酸氢二钠组成。
由于磷酸二氢钠是一种弱酸，在酸性和中性溶液中解离程度较低。
然而，当向溶液中加入强碱（如氢氧化钠）时，磷酸二氢钠会解离并释放出氢离子。这些离子与氢氧根离子结合，形成水分子。
同时，也会生成磷酸氢二钠。
由于该过程将氢氧化钠转化为弱碱磷酸氢二钠，溶液的 pH 值仅略有上升。
在碱性条件下，磷酸氢钠不会解离。
但是，当向溶液中加入盐酸等强酸时，磷酸氢二钠会结合氢离子，形成磷酸二氢钠。
由于该过程将 HCl 转化为弱酸磷酸二氢钠，溶液的 pH 值仅略有下降。
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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.