Hydrogen ion concentration of water is largely changed by addition of very small quantity of an acid or a base to it. Thus, one drop of a strong concentrated acid (say HCl) added to a litre of water makes it sufficiently acidic raising its H+ ion concentration to about 5000 times. Similarly, just two drops of strong alkali (say NaOH) added to water make it sufficiently basic, decreasing its H+ ion concentration to about a million times. Yet for many purposes we may need a solution with a fixed pH which does not change much on dilution or adding to it a small amount of any acid or base. Such a solution is called a buffer solution or simply buffer.
In simple words, a buffer solution is a system, which maintains its hydrogen (or hydroxyl) ion concentration at an approximately constant level, which does not change by adding water, any acid or base to it. It is not true that there is absolutely no change in the pH of a buffer solution by adding an acid or a base to it. However, the change is negligible which can be taken as practically no change.
In general, buffer solutions contain either a weak acid in presence of a rather high concentration of its conjugate base, or a weak base in presence of a rather high concentration of its conjugate acid. Strong acids and strong bases seldom form buffer because they are completely ionized. Following are some examples of common buffer solutions.
Applications of Buffers
Buffers with varying pH-range find a wide application in various processes, as described below:
In biological systems. Blood is the best example of a buffer solution. It consists of PO43-, HCO3-, and proteins (bases) and has a pH = 7.35 to 7.45. Consequently the blood always remains slightly alkaline inspite of many acidic foods we take.
- The pH of blood and other biological systems help the life processes go on normally. Sudden changes in their pH might prove fatal.
- Buffers are highly useful in industrial processes, such as manufacture of paper, dyes, inks, paints, drugs, antibiotics, etc., and working of latex, tanning of leather, laundry and so on.
- For healthy seeding and growth of crops; the soil needs to be maintained at a constant pH by means of suitable buffer solutions. Buffer of various pH are also of vital importance in the preparation of dairy products, such as condensed milk and processed cheese; and in preservation of various types of foods and fruits.