Що таке буфер?

What is a buffer?

Ultimately, a buffer helps prevent fast, dramatic change! In chemistry, we come across buffers mainly in titration curves which deal with pH. Buffers are also commonly used in biology, if an experiment needs to be kept at a specific pH for stability purposes or enzymatic activity. A fun fact is our blood’s pH is actually regulated by a buffer called the bicarbonate buffer system.

Buffers always slow down a change in pH caused by the addition of an acid or base to a solution.

But what is a buffer?

$\color{#0CB1B1}{\text{Buffers are aqueous solutions that consist of either of the following:}}$

$\color{#0CB1B1}{\text{1.Weak acid + its strong conjugate salt}}$

$\color{#0CB1B1}{\text{2.Weak base + its strong conjugate salt}}$

Acidic buffers buffer acidic solutions, basic buffers buffer basic solutions. Keep in mind, to identify a buffer that forms we are looking for only a weak acid or a weak base and the conjugate salt product.

Any other helpful information?

As previously mentioned, a buffer is a weak acid or base and the appropriate conjugate salt. The titration of a strong acid/base with a strong acid/base does not ever form a buffer; therefore, the pH changes relatively quickly to reach the equivalence point and ultimately the endpoint.

The optimal activity of a buffer is $pK_{a}\pm1$, but a buffer works most effectively when there are equal amounts of acid/base and the appropriate conjugate product. What point on a titration curve does this information - equal concentrations of acid and base - correspond to? The half-equivalence point!

The Henderson-Hasselbach equation, below, can help us to understand why. When there are equal amounts of acid and conjugate base, pH is equal to $pK_{a}$. Note that this equation is the same for a base and its conjugate acid, the variables are just slightly different.

$$pH=pK_{a}+log(\frac{A^{-}}{HA})$$

The principle behind a buffer system is Le’ Chatelier’s principle. A buffer system is in dynamic equilibrium between the starting material and products made from the titration. Le Chatelier’s principle tells us that a reaction will move in a way to relieve some of the stress due to the addition of a concentrated reactant or product.

Only when a buffer becomes too overwhelmed and is totally reacted will the pH continue to change dramatically as if there were no buffer.

References: 1

(Video) What is a Buffer?

Video source by: Sarah Chem

A buffer is defined as a a solution that resists a change in pH within a specific pH range. Buffers can be selected based on the pH range that is best for the reaction.

A buffer is made of a weak acid or weak base along with the conjugate salt of the weak acid/base. This salt has the conjugate or a compound differing by one proton.

We can examine compound combinations to determine whether they create a buffer. HCl cannot be used in a buffer because it is a strong acid. $HClO$ and $LiClO_2$ are not a conjugate pair and therefore do not form a buffer. $LiClO_2$ breaks down to $Li^+$ and $ClO_2^-$. $ClO_2^-$ and $ClO^-$ are not the same anions and differ by any oxygen. $HF$ and $KF$ is a buffer solution. $HF$ is a weak acid and $F-$ is the conjugate to the acid. $CH_3NH_2$ is a weak base and $CH_3NH_3Cl$ is the conjugate acid, so this forms a buffer.