Buffers
Buffers resist changes in pH.
About this topic
A buffer is a solution that resists changes in pH when small amounts of acid or base are added. It contains a weak acid and its conjugate base (such as acetic acid and acetate) or a weak base and its conjugate acid. Added H+ is consumed by the base component and added OH− by the acid component.
The pH of a buffer is found with the Henderson-Hasselbalch equation: pH = pKa + log([A−]/[HA]). A buffer works best when the two components are in similar amounts, so pH is near pKa, and its capacity depends on how much of each is present. Too much strong acid or base will use up one component and the buffer fails.
Worked example: a solution with 0.10 M acetic acid (pKa 4.76) and 0.10 M sodium acetate has pH 4.76. Adding a small amount of HCl converts some acetate to acetic acid, shifting the ratio slightly so pH changes very little compared with unbuffered water. Blood is buffered by carbonic acid and bicarbonate to stay around pH 7.4; without it, small amounts of acid from exercise would be fatal. Buffers are used in shampoos, medicines, swimming pools, food and fermentation.
A misconception is that buffers prevent any pH change; they only limit it. Another is that any weak acid solution is a buffer; you need the conjugate base present as well.
Key ideas
- Weak acid plus conjugate base
- Blood is buffered
- Use Henderson–Hasselbalch
Quick check
Use cases: where Buffers helps
- Homework: review the key idea behind Buffers before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Buffers without notes.
- Visual learning: play with the interactive lab to see how Buffers changes when you adjust its inputs.
- Teaching a friend: explain Buffers in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Buffers?
Buffers resist changes in pH.
What will I learn in Buffers?
Weak acid plus conjugate base. Blood is buffered. Use Henderson–Hasselbalch.
Is Buffers part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Buffers lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Buffers?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.