Question

Which of the following can be classified as buffer solutions? $$ \begin{array}{l}{\text { a. } 0.25 M \mathrm{HBr}+0.25 \mathrm{M} \mathrm{HOBr}} \\ {\text { b. } 0.15 \mathrm{M} \mathrm{HClO}_{4}+0.20 \mathrm{M} \mathrm{RbOH}} \\ {\text { c. } 0.50 \mathrm{M} \mathrm{HOCl}+0.35 \mathrm{MKOCl}}\end{array} $$ $$ \begin{array}{l}{\text { d. } 0.70 M \mathrm{KOH}+0.70 \mathrm{M} \text { HONH_ }} \\ {\text { e. } 0.85 \mathrm{M} \mathrm{H}_{2} \mathrm{NNH}_{2}+0.60 M \mathrm{H}_{2} \mathrm{NNH}_{3} \mathrm{NO}_{3}}\end{array} $$

Short answer

The buffer solutions are: c. \(0.50 M HOCl + 0.35 M KOCl\) e. \(0.85 M H_2NNH_2 + 0.60 M H_2NNH_3NO_3\)

Step-by-step solution

Identify weak acids/bases and their conjugate pairs in each solution

We need to identify which components are weak acids, weak bases, and their respective conjugate pairs in each solution: a. HBr (strong acid) and HOBr (weak acid) b. HClO₄ (strong acid) and RbOH (strong base) c. HOCl (weak acid) and KOCl (conjugate base of HOCl) d. KOH (strong base) and HONH₂ (weak base) e. H₂NNH₂ (weak base) and H₂NNH₃NO₃ (conjugate acid of H₂NNH₂)

Determine if the solutions contain a weak acid/base and their conjugate pairs

A buffer solution must contain a weak acid and its conjugate base, or a weak base and its conjugate acid. We will analyze each solution to see if they meet this criterion: a. This solution contains a strong acid and a weak acid; therefore, it is not a buffer solution. b. This solution contains a strong acid and a strong base; therefore, it is not a buffer solution. c. This solution contains a weak acid and its conjugate base; therefore, it is a buffer solution. d. This solution contains a strong base and a weak base; therefore, it is not a buffer solution. e. This solution contains a weak base and its conjugate acid; therefore, it is a buffer solution.

Determine which solutions are buffer solutions

Based on our analysis, we can conclude that the following solutions are buffer solutions: c. 0.50 M HOCl + 0.35 M KOCl e. 0.85 M H₂NNH₂ + 0.60 M H₂NNH₃NO₃

Key concepts

Weak Acids

Weak acids are a fun and fascinating part of chemistry! They are acids that do not completely dissociate in water, meaning they release fewer hydrogen ions (\( ext{H}^+ \)) than strong acids do. This partial dissociation is what makes them weak, but it's also what makes them useful in buffer solutions. For example, acetic acid (\( ext{CH}_3 ext{COOH} \)) is a weak acid. In its solution, only a fraction of the acetic acid molecules donate protons to form acetate ions and hydrogen ions.

• Weak acids are essential for buffers because they provide \( ext{H}^+ \) slowly to maintain pH stability.
• Common examples include acetic acid and citric acid.
• They are distinct from strong acids, like HCl, which dissociate almost completely.

By understanding weak acids, we can appreciate their role in forming stable pH environments in various chemical processes.

Conjugate Base

The conjugate base is what you get after a weak acid donates a hydrogen ion (\( ext{H}^+ \)). It's like a best friend that remains even when the main player (the acid) has to give something away. For instance, when acetic acid (\( ext{CH}_3 ext{COOH} \)) donates an \( ext{H}^+ \), it becomes acetate (\( ext{CH}_3 ext{COO}^- \)), its conjugate base.

• In a buffer solution, the conjugate base helps resist changes in pH by accepting \( ext{H}^+ \) when there is an excess.
• They are typically the negatively charged part of a weak acid/base pair.
• Examples include acetate (\( ext{CH}_3 ext{COO}^- \)) and carbonate (\( ext{CO}_3^{2-} \)).

Conjugate bases are crucial for understanding how buffers work efficiently to maintain consistent pH levels.

Weak Bases

Weak bases are the flip side of weak acids in the world of chemistry buffers! These are bases that do not completely ionize in solution, which means they do not fully release hydroxide ions (\( ext{OH}^- \)). One classic example of a weak base is ammonia (\( ext{NH}_3 \)). In water, ammonia takes up hydrogen ions, but not all ammonia molecules will interact this way.

• Weak bases are central to forming buffers that can neutralize small amounts of added acid.
• They usually exist in equilibrium with their conjugate acids in solution.
• Examples of weak bases include ammonia and bicarbonate (\( ext{HCO}_3^- \)).

Understanding weak bases helps us see how buffers maintain a steady environment when faced with acids.

Conjugate Acid

In the dance of ions, the conjugate acid is what a weak base transforms into after it accepts a hydrogen ion (\( ext{H}^+ \)). It completes the duo that works together in buffers. For example, when ammonia (\( ext{NH}_3 \)) accepts an \( ext{H}^+ \), it becomes ammonium (\( ext{NH}_4^+ \)), its conjugate acid.

• Conjugate acids partner with weak bases to balance pH by releasing \( ext{H}^+ \) when needed.
• They generally form from the parent weak base and won't dissociate completely.
• Common conjugate acids include ammonium (\( ext{NH}_4^+ \)) and hydronium (\( ext{H}_3 ext{O}^+ \)).

Grasping the role of conjugate acids is key to understanding how buffer solutions operate through intricate ion balancing.