Question

A buffer is prepared by dissolving \(\mathrm{HONH}_{2}\) and \(\mathrm{HONH}_{t} \mathrm{NO}_{3}\) in some water. Write equations to show how this buffer neutralizes added \(\mathrm{H}^{+}\) and \(\mathrm{OH}^{-}\)

Short answer

The buffer neutralizes added H+ ions through the reaction: HONH2 + H+ \( \rightarrow \) HONH3+, and neutralizes added OH- ions through the reaction: HONH2 + OH- \( \rightarrow \) HONH- + H2O.

Step-by-step solution

Understand buffer solutions

A buffer solution is a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. Buffer solutions resist changes in pH when small amounts of strong acids or bases are added. In this exercise, we have a buffer solution prepared by dissolving HONH2 and HONH2NO3.

Identify acidic and basic components of the buffer

First, we must determine the acidic and basic components of the buffer solution. We can do this by considering the dissociation of the given substances in water: HONH2 can donate a proton (H+) to form its conjugate base: HONH2 \( \rightleftharpoons \) HONH- + H+ HONH2NO3 is the salt of HONH2 and HNO3, formed by the reaction of HONH2 (weak base) and HNO3 (strong acid): HONH2 + HNO3 \( \rightarrow \) HONH2NO3 + H2O Since HNO3 is a strong acid, its dissociation in water can be considered complete: HNO3\( \rightarrow \) H+ + NO3- The dissociation of HONH2NO3 will therefore be: HONH2NO3\( \rightleftharpoons \) HONH2 + NO3- So, in this buffer: - HONH2 (a weak base) serves as the basic component. - The HONH2NO3 (the salt of HONH2) ionizes in water to produce HONH2 and NO3-, where NO3- is the conjugate base of the strong acid HNO3, serving as the acidic component.

Write the equations for neutralization of added H+ and OH- ions

Now, we will write the equations that show how the buffer's components neutralize added H+ and OH- ions. Neutralizing added H+: When H+ ions are added to the buffer, the basic component HONH2 reacts with the H+ ions to form its conjugate acid: HONH2 + H+ \( \rightarrow \) HONH3+ Neutralizing added OH-: When OH- ions are added to the buffer, the acidic component (NO3- ions from HONH2NO3) reacts with the OH− ions to form water and the conjugate base HONH2: HONH2 + OH- \( \rightarrow \) HONH- + H2O In summary, the buffer consisting of HONH2 and HONH2NO3 neutralizes added H+ ions through the following reaction: HONH2 + H+ \( \rightarrow \) HONH3+ And it neutralizes added OH- ions through this reaction: HONH2 + OH- \( \rightarrow \) HONH- + H2O

Key concepts

Acid-Base Neutralization

Acid-base neutralization is a chemical reaction where an acid and a base react to form water and salt. This process effectively reduces the strength of the acid and the base involved. In simpler terms, it's a battle between the opposites — acids releasing hydrogen ions ( H^+ ) and bases releasing hydroxide ions ( OH^- ). When they encounter each other, they combine to form water ( H_2O ), neutralizing their effects.

In buffers, this concept plays a critical role. When a strong acid or base is added to the buffer, the weak acid/base in the buffer reacts with the strong counterpart in the added solution, absorbing the extra hydrogen or hydroxide ions and minimizing pH changes.

• The buffer's weak acid will react with any added base ( OH^- ) to form water, decreasing the base's effect.
• The buffer's weak base will react with any added acid ( H^+ ) to form its conjugate acid, reducing the acid's impact.

This ability to neutralize small amounts of added acid or base is why buffers are so effective in maintaining pH stability.

Conjugate Base

A conjugate base is what remains after an acid donates a proton ( H^+ ) during a chemical reaction. For any weak acid in a buffer solution, this conjugate base plays a millennium-old game of balance. It ensures the buffer can resist changes in pH upon the addition of acids.

Consider a weak acid, HA. When it releases a proton, it becomes its conjugate base, A-. This A- is then 'prepared' or 'armed' to grab any extra hydrogen ions that might show up, preventing them from affecting the solution's pH.

• Example: The weak acid HONH_2 becomes its conjugate base HONH^- .
• Upon encountering excess H^+ , HONH^- quickly forms HONH_3^+ , stabilizing the pH.

This game of exchanging a proton and capturing it back keeps the buffer functioning effectively, maintaining the desired pH.

Weak Acid

Weak acids play a fundamental role in buffer systems, acting as the initial line of defense against drastic pH changes. Unlike strong acids, they do not dissociate completely in water. Instead, they establish an equilibrium between the undissociated acid and its ions.

Let's explore the behavior of weak acids within a buffer. When a strong base is added:

• They respond by releasing hydrogen ions ( H^+ ) to counteract any increase in hydroxide ions ( OH^- ).
• This release means the weak acid's natural tendency to stay undissociated helps maintain the pH.

These acids release their hydrogens gradually, perfectly matching the need for adjustments in pH without overshooting or overreacting.
This gradual release process is a safety net against practices where the strong acid would have caused sharp pH variations.

pH Resistance

The primary benefit of buffer solutions is their ability to resist changes in pH, known as pH resistance. This quality is central to many chemical and biological systems, where maintaining a stable pH is crucial.

Buffers are crafted from a weak acid and its conjugate base, or a weak base and its conjugate acid. This combination molds an environment robust against pH swings by actively neutralizing added acids or bases.

• When hydrogen ions ( H^+ ) are added, they are absorbed by the conjugate base, forming the undissociated weak acid.
• If hydroxide ions ( OH^- ) are added, the weak acid responds by forming water and its conjugate base.

In either case, these reactions ensure that the pH remains fairly constant. This system's design makes buffers indispensable in laboratory settings and biological systems alike, where enzymes and other proteins are highly sensitive to pH changes.