30.14
リン酸緩衝液
リン酸緩衝系は、体内の pH 安定性を維持するための重要な生物学的機構です。この系は主に、弱酸として機能するリン酸二水素ナトリウム (NaH_2PO_4) と弱塩基として機能するリン酸水素ナトリウム (Na_2HPO_4) の 2 つの成分によって機能します。
リン酸二水素ナトリウムは、中性または酸…
リン酸緩衝系は、尿や細胞内液に不可欠です。
リン酸二水素ナトリウムとリン酸水素ナトリウムで構成されています。
リン酸二水素ナトリウムは弱酸であるため、酸性および中性の溶液ではあまり解離しません。
しかし、水酸化ナトリウムなどの強塩基を溶液に導入すると、リン酸二水素ナトリウムが解離して水素イオンが放出されます。これらのイオンは水酸化物イオンと結合し、水分子を形成します。
同時に、リン酸水素ナトリウムも形成されます。
このプロセスは水酸化ナトリウムを弱塩基リン酸水素ナトリウムに変換するため、溶液のpHはわずかに上昇するだけです。
リン酸水素ナトリウムは、アルカリ性条件下では解離しません。
しかし、塩酸のような強酸を溶液に加えると、リン酸水素ナトリウムが水素イオンを取り込み、リン酸二水素ナトリウムを形成します。
このプロセスによりHClが弱酸性リン酸二水素ナトリウムに変換されるため、溶液のpHはわずかに低下します。
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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.