Question

The complete phosphate buffer system is based on four substances: \(\mathrm{H}_{3} \mathrm{PO}_{4}, \mathrm{H}_{2} \mathrm{PO}_{4}^{-}, \mathrm{HPO}_{4}^{2-},\) and \(\mathrm{PO}_{4}^{3-}\). What different buffer solutions can be made from these substances?

Short answer

Three buffer solutions can be made: \( \mathrm{H}_3\mathrm{PO}_4/\mathrm{H}_2\mathrm{PO}_4^- \), \( \mathrm{H}_2\mathrm{PO}_4^- / \mathrm{HPO}_4^{2-} \), \( \mathrm{HPO}_4^{2-}/\mathrm{PO}_4^{3-} \).

Step-by-step solution

Understanding Buffers

A buffer solution is a system that resists changes in pH when small amounts of acids or bases are added. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid.

Identify Conjugate Acid-Base Pairs

In the phosphate buffer system, the conjugate acid-base pairs are: \( \mathrm{H}_3\mathrm{PO}_4 / \mathrm{H}_2\mathrm{PO}_4^- \) and \( \mathrm{H}_2\mathrm{PO}_4^- / \mathrm{HPO}_4^{2-} \), and \( \mathrm{HPO}_4^{2-} / \mathrm{PO}_4^{3-} \).

Formulate Possible Buffers

Buffers can be made using the conjugate acid-base pairs identified: 1. \( \mathrm{H}_3\mathrm{PO}_4 \) and \( \mathrm{H}_2\mathrm{PO}_4^- \)2. \( \mathrm{H}_2\mathrm{PO}_4^- \) and \( \mathrm{HPO}_4^{2-} \)3. \( \mathrm{HPO}_4^{2-} \) and \( \mathrm{PO}_4^{3-} \)

Conclusion on Buffer Systems

Thus, the following three buffer systems can be created from the phosphate compounds: 1. \( \mathrm{H}_3\mathrm{PO}_4 / \mathrm{H}_2\mathrm{PO}_4^- \)2. \( \mathrm{H}_2\mathrm{PO}_4^- / \mathrm{HPO}_4^{2-} \)3. \( \mathrm{HPO}_4^{2-} / \mathrm{PO}_4^{3-} \)

Key concepts

Buffer Solutions

Buffer solutions play a crucial role in maintaining the pH balance in various chemical and biological systems. They are specially formulated to resist changes in pH upon the addition of small amounts of acid or base. This resistance to pH change is what makes buffer solutions invaluable in processes that require a stable pH environment.

Buffer solutions typically consist of a weak acid and its conjugate base, or a weak base and its conjugate acid. In the case of the phosphate buffer system, which is common in biological and chemical processes, the distinct compounds can be rearranged to form various buffer solutions.

The beauty of buffer systems is their adaptability. Specifically, the phosphate buffer includes multiple substances with differing capacities to either donate or accept hydrogen ions. This versatility allows it to maintain pH levels across a broad spectrum of conditions. Overall, buffers are essential in laboratory settings, environmental systems, and the human body, among other applications.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs are fundamental to understanding how buffer solutions function. These pairs consist of two species that differ by one proton (H⁺). The concept of conjugate acid-base pairs allows us to convey the reversible nature of acid-base reactions.

In the phosphate buffer system, several conjugate acid-base pairs can be formed:

• o(\(\mathrm{H}_3\mathrm{PO}_4 / \mathrm{H}_2\mathrm{PO}_4^- \)) - Here, \(\mathrm{H}_3\mathrm{PO}_4\) is the acid and \(\mathrm{H}_2\mathrm{PO}_4^-\) its conjugate base.
• o(\(\mathrm{H}_2\mathrm{PO}_4^- / \mathrm{HPO}_4^{2-} \)) - In this pair, \(\mathrm{H}_2\mathrm{PO}_4^-\) acts as the acid while \(\mathrm{HPO}_4^{2-}\) is the conjugate base.
• o(\(\mathrm{HPO}_4^{2-} / \mathrm{PO}_4^{3-}\)) - Lastly, \(\mathrm{HPO}_4^{2-}\) can donate a proton to form the conjugate base \(\mathrm{PO}_4^{3-}\).

Understanding these conjugate pairs is key to preparing buffer solutions. Each pair influences the buffer's characteristics and effectiveness at different pH levels. Consequently, by selecting appropriate pairs, chemists and biologists can tailor buffer solutions to specific needs.

pH Resistance

One of the hallmark features of buffer solutions is their ability to resist changes in pH, a characteristic often referred to as pH resistance. This property is vital in preventing drastic shifts in pH that could affect chemical reactions or biological functions.

The phosphate buffer system is an excellent example of pH resistance in action. Because it involves multiple stages of proton donation and acceptance through its conjugate acid-base pairs, it can stabilize pH across a wide range.

• This makes phosphate buffers especially valuable in biological systems, where maintaining a narrow pH range is crucial for enzyme function and other biochemical processes.
• Phosphate buffers are also frequently used in industrial applications where consistent pH levels are needed.

Ultimately, the pH resistance provided by buffer solutions like the phosphate buffer system is essential for the stability and efficiency of many scientific, industrial, and physiological processes.