Buffer Solutions

A buffer solution is a system that maintains its hydrogen or hydroxyl ion concentration at an approximately constant level. This level does not change by adding water or small amounts of acid or base. Buffer solutions can resist pH change when an acid or base is added. The solution can be that of an acid that is weak and its conjugate base, or vice versa. Let us learn all there is to learn about buffer solutions. This will help make you understand what buffer exactly is. 

Types of Buffer Solution

There are two types of buffer solution in existence- acidic buffer and alkaline buffer. 

• Acidic Buffer Solution:  

A pH value of below 7 characterizes an acidic buffer solution. The production of an acidic buffer solution takes place from an acid that is weak and one of its salts. In most cases, this salt is sodium salt.

An ethanoic acid and sodium ethanoate in the solution mixture would serve as a good example here. In such a solution, if the molar concentrations of acid and the salt turn out to be equal, it would provide a 4.76 pH. As long as the concentrations are the same, it would not matter what the concentrations were. 

A variation can be brought about in the buffer solution’s pH by altering the ratio of acid to salt. Another way to bring about the variation is by selecting a different type of acid and its salt.

• Alkaline Buffer Solution:

An alkaline buffer solution is the other type of buffer solution. An alkaline buffer solution is characterized with an above 7 pH. The productions of these solutions take place from a weak base and one of its salts.

An ammonia solution and ammonium chloride solution mixture is a suitable example we can see here. If someone mixes these solutions in equal molar proportions, there would be a 9.25 pH in the resulting solution. Again, as long as the concentrations are the same, it will not matter what the concentrations were.

Henderson – Hasselbalch Equation

This equation is used in the calculation of the pH value of buffer solutions. It is useful in understanding what buffer exactly is. The expression of this particular equation can take place as: 

pH = pKₐ + log ([A⁻]/[HA]).

• For Acidic Buffer Solutions:

Consider a mixture of HA (weak acid) and its salt, NaA.

A weak acid is undergoing a reversible reaction:

HA + H20 ⇆H3O+ + A-

Because of an increase in the concentration of A- ions, the dissociation of a weak acid is suppressed (common ion effect).

The concentration of weak acid molecules is taken as the concentration of HA, and the concentration of salt is A- ions.

Thus, [HA] = [ acid ] and [salt] = [A-]

The whole acid is assumed as completely dissociated.

      pH = pKa + log10 [salt] / [acid]

This equation is called Henderson – Hasselbalch Equation. It helps calculate the pH value of the buffer solutions if the acid and the salt concentration are known.

• For Basic Buffer Solutions:

In the same way, the pH value of a basic buffer can be calculated. Let a basic buffer be a mixture of a weak base (BOH) and its salt BA (or B+)

               BOH → B+ + OH-

The salt BA provides B+ ions, and the salt is fully ionized. Therefore, the weak base is assumed to be completely unionized.

      poH = pKb + log [salt] / [base]

This is also known as Henderson – Hasselbalch equation.

Buffer Capacity or Buffer Index

The buffer capacity is defined as the amount (number of moles) of the acid or base, which changes its pH by unity when added to one litre of the given buffer solution.

Buffer Capacity or Buffer Index

= Number of acid or alkali added per litre/

   Change in pH

= dn acid or base/ dpH 

Mathematically, it is expressed as:

 Beta = d[B] /d pH or -d[A] / d pH

Where d[B]  represents the change that takes place in the concentration of base

           d[A] represents the change that takes place in the concentration of acid 

           dpH represents the change that takes place in the buffer solution’s pH

Application of Buffers

Below are the various applications of buffer solutions:

• In biological systems, blood is the best example of a buffer solution. It has a pH between 7.35 to 7.45. Consequently, the blood always remains slightly alkaline despite the acidic foods we intake.

• Buffers are highly useful in industrial processes such as paper, dyes, inks, paints, drugs, antibiotics, etc., working on latex, leather tanning, laundry, etc.

• Using suitable buffer solutions, the pH level of any soil can be maintained for healthy seeding and growth of crops. Buffers of various pH values are also of vital importance in preparing dairy products such as condensed milk and processed cheese and preserving multiple types of foods and fruits.

Conclusion

Buffer solutions are those that can resist pH change when someone adds acid or base to it. These solutions have significant importance in acid-base chemistry. When it comes to the types of buffer solution, they are of two types. One is the acidic buffer solution, and the other is the alkaline buffer solution. The expression of the Henderson – Hasselbalch Equation is pH = pKₐ + log([A⁻]/[HA]). Buffer Capacity or Buffer Index is also an important part of studying buffer solutions. There are several applications of buffers in the modern world.