Question

Explain how the phosphate buffer system will react to buffer a strong acid. (p. 443)

Short answer

#tag_title# Short Answer #tag_content# When a strong acid is added to the phosphate buffer system, the dihydrogen phosphate ions (H2PO4^-) accept the protons (H+) from the strong acid, forming phosphoric acid (H3PO4). This reaction helps maintain a relatively constant pH in the solution, providing a buffering effect against the strong acid. The reversible nature of the reaction allows the phosphate buffer system to adjust and maintain the pH within an optimal range for biological systems.

Step-by-step solution

Understand the phosphate buffer system

The phosphate buffer system is an important buffer present in biological systems, such as human blood and cells. It is mainly composed of a mixture of two different ions: hydrogen phosphate ions (HPO4^2-, also called dihydrogen phosphate) and dihydrogen phosphate ions (H2PO4^-, also known as monohydrogen phosphate). These two ions can react with each other or with water to form different species in the system, and thus maintain a relatively constant pH in the presence of added strong acids or strong bases.

Determine the reaction with a strong acid

When a strong acid is added to the phosphate buffer system, it will donate a proton (H+) to the system. The dihydrogen phosphate ion (H2PO4^-) will be the species responsible for accepting this proton, as it acts as a weak base. The reaction can be represented as follows: $$H2PO{4}^{-}+H^{+}\leftrightarrow H3PO4$$ In this reaction, the dihydrogen phosphate ion (H2PO4^-) combines with a proton (H+) to form phosphoric acid (H3PO4). This reaction is reversible, meaning it can proceed in both forward and reverse directions, depending on the conditions in the solution.

Understand the buffering effect of the phosphate buffer system

The phosphate buffer system is able to maintain a relatively constant pH in the presence of a strong acid because it can accept or donate protons, depending on the conditions in the solution. When a strong acid is added, the dihydrogen phosphate ions (H2PO4^-) in the buffer system will readily accept the protons, thus preventing a significant change in the concentration of hydrogen ions (H+) in the solution. This means that the pH of the solution remains relatively constant, despite the addition of the strong acid. Due to the reversible nature of the reaction, the phosphate buffer system can adjust to changes in the solution and maintain the pH within an optimal range.

Recap the phosphate buffer system's reaction to a strong acid

To summarize, when a strong acid is added to the phosphate buffer system, the dihydrogen phosphate ions (H2PO4^-) present in the system will accept the protons (H+) from the strong acid, forming phosphoric acid (H3PO4). This reaction helps to maintain a relatively constant pH in the solution, providing a buffering effect against the strong acid. The reversible nature of the reaction allows the phosphate buffer system to adjust and maintain the pH within an optimal range for biological systems.

Key concepts

Acid-Base Balance

Acid-base balance in the human body is a crucial aspect of maintaining physiological stability. This balance refers to the mechanism by which the body keeps its internal environment, particularly the blood, at a relatively constant pH level, typically around 7.35 to 7.45. The pH scale, running from 0 to 14, measures how acidic or basic a solution is, with a pH less than 7 being acidic and greater than 7 being basic (or alkaline).

The body has several systems in place to manage pH levels, including the respiratory system, the kidneys, and various buffer systems in bodily fluids. Among these, the phosphate buffer system, present in the plasma and the cells, is an integral component. It consists of a mix of phosphate salts that work together to prevent drastic pH changes, especially during metabolic processes where acids or bases might be produced or consumed. When a strong acid is added to this system, the buffer will minimize the alteration of the pH by converting the dihydrogen phosphate ion $H2PO{4}^{-}$ into phosphoric acid $H3PO4$, thus 'absorbing' the additional hydrogen ions that would otherwise cause acidification of the fluid.

Buffering Effect

The buffering effect can be envisioned as the biochemical equivalent of a shock absorber—it helps to dampen the impact of external changes on the pH of a solution. A buffer system generally comprises a weak acid and its conjugate base (or a weak base and its conjugate acid). This pairing is vital as they can rapidly accept or donate protons ($H^{+}$) in response to pH changes.

In the scenario where a strong acid is introduced to a solution, like in our phosphate buffer system example, the conjugate base of the buffer ($H2PO{4}^{-}$) accepts the excess protons, forming its corresponding weak acid $H3PO4$. By sequestering the free protons, the dihydrogen phosphate ion helps to keep the pH from dropping significantly, showcasing the system's ability to maintain homeostasis. This reversible reaction is fundamental, meaning that should the solution become too basic, the weak acid can donate protons back into the solution, thus correcting the pH imbalance.

Biochemical Reactions

Biochemical reactions are processes that sustain life, taking place within cells and tissues of living organisms. These reactions often involve the transformation of molecules into others via a series of steps, catalyzed by enzymes. Acid-base balance is crucial here because most enzymes function optimally within a narrow pH range. If the pH of the cellular environment strays too far from its optimum, the structure and activity of the enzymes can be compromised, leading to dysfunction in metabolic pathways.

Buffer systems such as the phosphate buffer are pivotal in maintaining pH stability, thereby allowing biochemical reactions to proceed unimpeded. The phosphate buffer system, in particular, is versatile; it functions both inside the cells and in the extracellular fluids, including the blood. This versatility is key in a variety of cellular processes, ranging from energy metabolism to DNA synthesis, where the maintenance of a stable pH is essential for the enzymes and proteins involved to perform efficiently.