pKa Calculator
Category: ChemistryHenderson-Hasselbalch Equation:
Buffer Preparation
1. Dissolve the indicated amounts in approximately 80% of the final volume.
2. Adjust pH using a pH meter if necessary.
3. Add water to reach the final volume.
Buffer Capacity
Effective pH Range: 3.8 - 5.8
Buffer Capacity: 0.058 mol/L/pH
Enter Multiple pKa Values
Species Distribution vs. pH
Predominant Species at pH 7.0
Titration Curve
Recommended Indicators
About pKa and Acid-Base Chemistry
Basic Concepts
The pKa value is the negative logarithm of the acid dissociation constant (Ka) and represents the pH at which exactly half of an acid is dissociated.
pKa = -log₁₀(Ka)
For acids, a lower pKa indicates a stronger acid, while for bases, a higher pKa of the conjugate acid indicates a stronger base.
Key Points:
- At pH = pKa, an acid is 50% ionised
- At pH = pKa + 1, an acid is approximately 91% ionised
- At pH = pKa - 1, an acid is approximately 9% ionised
- Buffer solutions work best when pH ≈ pKa (±1 pH unit)
Common pKa Values
| Compound | pKa | Useful pH Range |
|---|---|---|
| Phosphoric acid (1st) | 2.15 | 1.15 - 3.15 |
| Citric acid (1st) | 3.13 | 2.13 - 4.13 |
| Acetic acid | 4.76 | 3.76 - 5.76 |
| MES | 6.15 | 5.15 - 7.15 |
| Phosphoric acid (2nd) | 7.20 | 6.20 - 8.20 |
| TRIS | 8.06 | 7.06 - 9.06 |
| Carbonic acid (2nd) | 10.33 | 9.33 - 11.33 |
| Phosphoric acid (3rd) | 12.32 | 11.32 - 13.32 |
Understanding the pKa Calculator
The pKa Calculator is a handy tool for anyone working with acids and bases. It helps determine the strength of acids based on their pKa values. pKa is important because it tells us at what pH an acid will donate protons. This knowledge is vital in many fields, including Chemistry, biochemistry, and pharmaceuticals. With this calculator, you can easily explore acid-base relationships and make informed decisions in your experiments.
The Henderson-Hasselbalch Equation
One of the main features of the pKa Calculator is its ability to use the Henderson-Hasselbalch Equation. This equation relates pH, pKa, and the ratio of acid and its conjugate base. Here’s how it works:
- pH = pKa + log([A-]/[HA])
- This equation shows how pH changes based on the concentrations of the acid and base.
By using this equation, you can determine the pH of buffer solutions and understand how different components interact in a solution.
Buffer Preparation Made Easy
The calculator simplifies buffer preparation, allowing you to select common buffers like acetate or phosphate. You can also enter custom pKa values for unique scenarios. Entering the target pH and concentration of your buffer gives you precise amounts of acid and base needed. It even provides instructions on how to mix your buffers effectively, ensuring you achieve the desired pH.
Multiple pKa Analysis for Advanced Users
If you have multiple pKa values to consider, the pKa Calculator can handle that too. You can enter different pKa values and see how they affect your solution's pH across a range. This feature is particularly useful in research when dealing with complex mixtures. You can visually see the distribution of species in relation to pH, helping you make educated guesses about which form will dominate at certain pH levels.
Visualising Titration Curves
The pKa Calculator also allows users to generate titration curves. These curves show how the pH of a solution changes as you add titrant. You can select the type of titration—whether it’s a strong acid with a strong base or another combination. This visual representation aids in understanding acid-base reactions and their equivalence points, making it easier to predict how pH will shift during your experiments.
Accessing Important Theoretical Concepts
The calculator doesn’t just crunch numbers; it also offers valuable theoretical insights. Users can learn about pKa, acid-base chemistry, and the significance of buffers all in one place. You can explore topics like percent ionization and buffer capacity, ensuring you have a solid foundation before diving into practical applications. The calculator serves as both a tool and a learning resource.
Quick Reference for Common pKa Values
In addition to calculations, the pKa Calculator provides a reference table with common pKa values. This feature saves time by giving you quick access to essential data. Here are a few examples:
- Acetic acid: pKa 4.76
- Phosphoric acid (1st): pKa 2.15
- Citric acid (1st): pKa 3.13
Having this information on hand means you can make quicker decisions when selecting compounds for your experiments.
Conclusion: A Must-Have Tool for Scientists
The pKa Calculator is an indispensable resource for anyone involved in chemistry or related fields. Its user-friendly features, combined with educational content, make it suitable for students and professionals alike. Whether you’re preparing buffers, analysing multiple pKa values, or studying titration curves, this calculator has you covered. It's a practical companion for mastering acid-base chemistry.