Buffers: Definition, Components, and pH Calculation
Definition
Buffers
Buffers are solutions that resist changes in pH when small amounts of acid ($H⁺$ ions) or base ($OH⁻$ ions) are added.
Example
They play a critical role in maintaining pH stability in chemical reactions, biological systems (like blood), and industrial processes.
To understand how buffers work, consider this:
- If you add a strong acid to pure water, the pH drops significantly because there’s nothing in the water to counteract the influx of $H⁺$ ions.
- A buffer, however, "absorbs" most of these $H⁺$ ions, minimizing the pH change.
Analogy
- Think of a buffer as a sponge.
- Just as a sponge absorbs water to prevent spills, a buffer absorbs excess $H⁺$ or $OH⁻$ ions, preventing drastic pH changes.
Components of a Buffer
Every buffer consists of two key components:
- A weak acid and its conjugate base(e.g., $CH₃COOH$/$CH₃COO⁻$).
- A weak base and its conjugate acid(e.g., $NH₃$/$NH₄⁺$).
Example
Acetic Acid/Sodium Acetate Buffer
- Weak acid: Acetic acid ($CH₃COOH$)
- Conjugate base: Acetate ion ($CH₃COO⁻$)
- When a small amount of strong acid (e.g., HCl) is added, the acetate ion ($CH₃COO⁻$) reacts with the $H⁺$ ions, forming more acetic acid:
$$\text{CH₃COO⁻ (aq)} + \text{H⁺ (aq)} \rightarrow \text{CH₃COOH (aq)}$$ - When a small amount of strong base (e.g., NaOH) is added, the acetic acid reacts with the $OH⁻$ ions, forming water and more acetate ions:
$$\text{CH₃COOH (aq)} + \text{OH⁻ (aq)} \rightarrow \text{CH₃COO⁻ (aq)} + \text{H₂O (l)}$$
Example
Ammonia/Ammonium Chloride Buffer
- Weak base: Ammonia ($NH₃$)
- Conjugate acid: Ammonium ion ($NH₄⁺$)
- When a strong acid is added, the ammonia reacts with the $H⁺$ ions:
$$\text{NH₃ (aq)} + \text{H⁺ (aq)} \rightarrow \text{NH₄⁺ (aq)}$$ - When a strong base is added, the ammonium ion ($NH₄⁺$) reacts with the $OH⁻$ ions:
$$\text{NH₄⁺ (aq)} + \text{OH⁻ (aq)} \rightarrow \text{NH₃ (aq)} + \text{H₂O (l)}$$
Note
In both cases, the buffer absorbs the added acid or base, keeping the pH relatively constant.
Tip
Buffers work best when the concentrations of the weak acid and its conjugate base (or weak base and its conjugate acid) are roughly equal.
Applications of Buffers
Buffers are used in a wide range of real-world applications:
- Biological Systems: Blood is buffered by the carbonic acid/bicarbonate system to maintain a pH of 7.35–7.45, ensuring proper cellular function.
- Pharmaceuticals: Buffers stabilize the pH of medicines to enhance their effectiveness and shelf life.
- Industrial Processes: Buffers are used in dyeing fabrics, fermentation, and electroplating to maintain optimal pH conditions.
Self review
What are the two components of a buffer system?
