If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

# Buffer solutions

Buffer solutions maintain a stable pH by neutralizing added acids or bases. They consist of a weak acid and its conjugate base, which exchange protons and hydroxide ions to form water. The Henderson-Hasselbalch equation expresses the pH as a function of the PKa and the ratio of the base and acid concentrations.

## Want to join the conversation?

• Is it necessary for the buffer solution to have equal amounts of the conjugate acid-base pair?
• No, but that gives the best buffering capacity.
Ideally, the concentration of one should not be more than 10 times or less than one-tenth the concentration of the other.
• isn't H+ and H3O+ the same thing? That is what my ap chemistry teacher told us.
• Yes, they are just simpler representations of the real thing.
Various structures of hydrated proton of the type H⁺(H₂O)n are known all the way up to n =10 (H₂₁O₁₀⁺).
Let's keep it simple.
• So is a buffer that has the equal amounts of conjugate acid-base pair a neutral solution overall?
• Nope. Each buffer has a characteristic pH.
This can be explained by the Henderson Hasselbach equation! if [A-] = [HA] then...

pH=pKa + log [A-]/[HA]
pH=pKa + log (1)
pH=pKa + 0
pH=pKa *not*pH = 7

So buffers don't try to maintain neutrality, they try to keep the pH of the solution near their pKa.

• At , why don't we divide the H3O by the HA as well? I thought that both the H3O and the A must be divided by the denominator...?
• Well lets see, he did it like that because he wanted to show you how he could use the laws of logarithms to express it as a sum of logs, but as for your question consider 3 numbers A,B and C, I think multiplication is associative, so lets say (A*B)/C = (A/C)*B = (B/C)*A maybe an example would make it easier to see, though I could be wrong about this.
(2*4)/4 =2 also (2/4)*4 = 2 and (4/4)*2 = 2 maybe that helped? :3 Goodluck Buddy
• Doesn't having a weak acid/strong conjugate base affect the PH as well? how does it stay neutral, or close to that?
• So what does the buffer solution consist of? I'm confused about what a buffer actually is?
• A buffer solution is a solution that only changes slightly when an acid or a base is added to it. For an acid-buffer solution, it consists of a week acid and its conjugate base. For a basic-buffer solution, it consists of a week base and its conjugate acid.

The main purpose of a buffer solution is just to resist the change in pH so that the pH of the solution won't be much affected when we add an acid or base into it. The added acid or base is neutralized.
• say hydronium ions are added to a buffer solution and then neutralized by the conjugate base in the buffer solution leaving more of the conjugate acid than the conjugate base. Shouldn't that make the solution more basic overall? If that's true is the change in pH negligible?
• What happens if a buffer was made with only half as much acid compared to base? does equilibrium shift and buffer capacity lower?
• how to calculate the BUFFER CAPACITY??
(1 vote)
• Buffer Capacity (phi) = ( [H+] (or [OH-]) added ) / (change in pH of the buffer)
Intuitively, the buffer capacity must be the power of a buffer to resist pH change. And this intuition is supported by the fact that 'phi' tends to infinity in the limit of pH tending to zero.
(1 vote)
• Then why doesn't the weak acid in the buffer solution react with its conjugate base? Is it because the weak acid ionizes very little? Also, is it necessary for the pH of a buffer solution to be 7 or can it be different?
(1 vote)
• Because they are already in an equilibrium state. Unless you disturbed the equilibrium (in normal cases is changing the concentration), it won't react with one another.

It is not necessary for the pH to be 7. If you have an acidic-buffer solution, your pH would be lower than 7. If you have a basic buffer solution, your pH would be higher than 7.

Hope that helps :)
(1 vote)