In chemistry, a buffer solution is a mixture of a acidic or alkaline chemical with water and the chemical's salt. If the chemical is an acid, the salt will be its conjugate base; if the chemical is a base (or alkaline), the salt will be its conjugate acid. When prepared correctly, the buffer solution's pH will stay the same, even when small amounts of acid and base are added. Buffer solutions play an important role in chemical analysis, cleaning up chemical spills and in chemical manufacturing. There are four main ways to prepare a buffer solution. Choose which will work best for you, depending on the resources you have available.
- Skill level:
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Things you need
- Buffering agent: a weak acid or base
- Conjugate acid or base
- Deionised water
- Strong acid, such as HCl
- Strong base, such as NaOH
- Colorimetric paper or a pH meter
Use a table listing the amounts of bases and their conjugate acids, or acids and their conjugate bases, needed to make buffers of certain pHs (see Resources). Following the listed amounts, combine the components in water, verify the solution's pH, and correct with additional acid or base if necessary.
Mix the buffering agent in water, then to alter the pH of the solution with either a strong base (like NaOH) or a strong acid (like Hcl) until the pH is correct. Add water to reach the desired final volume of solution.
Prepare two separate solutions---the acid form and the alkaline form---of the buffer. By using a pH meter and adding one solution to the other, you can slowly bring the solution to the pH you are aiming for.
Use the Henderson-Hasselbalch equation to prepare a simple buffer solution (see Resources). Use the equation to determine what the ratio of the base form of the solution to the acid form will be when the buffer's pH is at the correct measurement. Make the solution, using the amounts indicated by the equation as a guide, and check and correct the pH if needed.
Four Ways to Make a Buffer Solution
Tips and warnings
- Always wear safety glasses when working with chemicals.
- Handle strong bases and acids with extreme care.
- Dispose of strong chemicals appropriately: never simply pour them down the drain.
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