Problem 11 - Chemistry for Allied Health

Question

Write the formula of the conjugate acid needed to form a buffer with each of the following weak bases. a. \(\mathrm{NH}_{3}\) b. \(\mathrm{CH}_{3} \mathrm{NH}_{2}\)

Step-by-Step Solution

Answer

The conjugate acid of \\( \mathrm{NH}_3 \\) is \\( \mathrm{NH}_4^+ \\), and of \\( \mathrm{CH}_3 \mathrm{NH}_2 \\) is \\( \mathrm{CH}_3 \mathrm{NH}_3^+ \\).

Step 1: Understanding Weak Bases and Buffers

A buffer solution is formed by a weak base and its conjugate acid. The conjugate acid of a base is formed by adding a proton (H⁺) to the base. For example, if the base is \(NH_3\), adding a H⁺ will form the conjugate acid.

Step 2: Identify the Conjugate Acid for Ammonia

For the weak base \( \mathrm{NH}_3 \), add a proton to form its conjugate acid. Therefore, the conjugate acid is \( \mathrm{NH_4^+} \).

Step 3: Identify the Conjugate Acid for Methylamine

For the weak base \( \mathrm{CH}_3 \mathrm{NH}_2 \), add a proton to get its conjugate acid. Thus, the conjugate acid is \( \mathrm{CH}_3 \mathrm{NH}_3^+ \).

Key Concepts

Weak Bases

Weak bases are substances that tend to partially accept protons, or hydrogen ions, when dissolved in water. Unlike strong bases, which fully dissociate in water, weak bases do not fully ionize.
Weak bases are crucial in the formation of buffer solutions because they can resist changes in pH when small amounts of an acid or base are added.
When a weak base accepts a proton, it turns into its conjugate acid, playing a vital part in maintaining the balance of the buffer solution.

Conjugate Acids

Conjugate acids are formed when a proton is added to a base. In the context of weak bases, the conjugate acid results from a weak base accepting this additional hydrogen ion.
For example, the conjugate acid of ammonia ( H_3) is ammonium ( H_4^+), and the conjugate acid of methylamine ( CH_3NH_2) is methylammonium ( CH_3NH_3^+).
These conjugate acids are essential components of buffer systems, allowing them to neutralize added acids in solutions, thus preventing drastic pH changes.

• Protonation of a base results in a conjugate acid.
• The reaction helps to maintain the balance of a buffer solution.

Ammonia Buffering

Ammonia ( H_3) is a classic example of a weak base that forms an effective buffer solution in combination with its conjugate acid, ammonium ( H_4^+).
When added to water, ammonia accepts protons to an extent, forming ammonium ions. These ions can then combine with additional hydroxide ions or donate protons to neutralize added acids.

• Ammonia can neutralize acids due to its basic properties.
• Ammonium ions act to resist pH changes by neutralizing added bases.

Such properties make ammonia-based buffers instrumental in many industrial and biochemical applications.

Methylamine Buffering

Methylamine ( CH_3NH_2), similar to ammonia, acts as a weak base that can be paired with its conjugate acid, methylammonium ( CH_3NH_3^+), to create a buffer solution.
When methylamine is in solution, it partially accepts protons, forming its conjugate acid. This system effectively dampens changes in pH when additional acids or bases are introduced to the solution.
The methylammonium ions can provide protons when a base is added or accept protons when an acid is present.

• Methylamine is suitable for maintaining pH in specific ranges.
• The combination with methylammonium ions ensures efficient buffering.

These characteristics make methylamine buffers valuable in chemical and biological systems.