Problem 215 - Introductory Chemistry Atoms First

Question

Is a solution that contains \(0.10 \mathrm{M} \mathrm{HBr}\) and \(0.10 \mathrm{M}\) NaBr a buffered solution? Why or why not?

Step-by-Step Solution

Answer

The solution containing 0.10 M HBr and 0.10 M NaBr is not a buffered solution because it does not contain a weak acid with its conjugate base or a weak base with its conjugate acid. HBr is a strong acid and cannot act as a buffer, while NaBr is the salt of a strong acid and a strong base, and its dissociation does not affect the pH of the solution.

Step 1: Identify the substances in the solution.

In the solution, there are two substances: HBr (hydrobromic acid) and NaBr (sodium bromide). HBr is a strong acid, and its conjugate base is Br⁻ (bromide ion). NaBr is the salt of a strong acid (HBr) and a strong base (NaOH); it will ionize completely into Na⁺ (sodium ion) and Br⁻ (bromide ion) in the solution.

Step 2: Determine the nature of the substances in the solution.

HBr, as a strong acid, dissociates completely in the solution and yields a high concentration of H⁺ ions, resulting in a low pH. Since it is a strong acid, it cannot act as a buffer. NaBr, as mentioned earlier, is the salt of a strong acid and a strong base, and its dissociation will not affect the pH of the solution. Therefore, NaBr cannot act as a buffer either.

Step 3: Analyze the solution's buffering capability.

For a solution to be a buffered solution, it needs to contain a weak acid and its conjugate base OR a weak base and its conjugate acid. In our case, the solution contains neither a weak acid with its conjugate base nor a weak base with its conjugate acid. HBr is a strong acid, and NaBr is a salt that does not contribute to the buffering system.

Step 4: Conclude whether the solution is a buffered solution or not.

Based on the analysis, neither HBr nor NaBr can act as buffers in the solution. Thus, the solution containing 0.10 M HBr and 0.10 M NaBr is not a buffered solution.

Key Concepts

Strong Acids

Strong acids are acids that completely dissociate in water. This means they release all of their hydrogen ions (\(H^+\)) into the solution. Because of this complete dissociation, strong acids result in a high concentration of hydronium ions, contributing to a very low pH. Some common examples of strong acids include:

• Hydrochloric acid (\(HCl\))
• Sulfuric acid (\(H_2SO_4\))
• Nitric acid (\(HNO_3\))

Hydrobromic acid (\(HBr\)) is also a strong acid.Due to their full dissociation, strong acids are not able to form buffer systems on their own. This is because buffer systems require a combination of a weak acid and its conjugate base to neutralize added acids or bases effectively.

Hydrobromic Acid

Hydrobromic acid (\(HBr\)) is a strong acid that dissociates completely in water, forming hydronium ions (\(H^+\)) and bromide ions (\(Br^-\)). This complete dissociation is characteristic of strong acids, which means HBr will not be part of a buffer system.The solution of hydrobromic acid will have a low pH due to the higher concentration of hydronium ions, making it a highly acidic environment. Here are some important points about hydrobromic acid:

• It is commonly used in the industry for the production of inorganic bromides.
• In laboratory settings, it can act as a strong acid catalyst in certain reactions.

Because hydrobromic acid does not participate in buffering, it cannot prevent significant changes in pH when acids or bases are added, differentiating it from buffer systems.

Sodium Bromide

Sodium bromide (\(NaBr\)) is a salt that results from the neutralization of the strong acid hydrobromic acid and the strong base sodium hydroxide (\(NaOH\)). In solution, sodium bromide dissociates completely into sodium ions (\(Na^+\)) and bromide ions (\(Br^-\)). Because the bromide ion is the conjugate base of the strong acid hydrobromic acid, it has virtually no ability to affect the pH of the solution.Sodium bromide does not contribute to any buffering effects because:

• Its ions are the result of a strong acid and a strong base.
• The solution will not resist pH changes effectively.

Therefore, sodium bromide by itself, or even in combination with other non-buffering components like strong acids, does not form a buffered solution.

Buffer Systems

Buffer systems are designed to maintain a stable pH in a solution when acids or bases are added. These systems are critical in many biological and chemical processes, where pH stability is crucial.Buffers usually consist of:

• A weak acid and its conjugate base (such as acetic acid and acetate ion).
• A weak base and its conjugate acid (such as ammonia and ammonium).

These components work together to neutralize added acids or bases, keeping the pH relatively constant.In the system discussed, with a solution of \(0.10 \, \text{M} \ HBr\) and \(0.10 \, \text{M} \ NaBr\), neither a weak acid nor a weak base is present. Instead, you have a strong acid with its salt, not capable of forming a buffer system. This is why the solution cannot effectively resist pH changes, demonstrating the necessity of weak acids or bases in buffer systems.