An acidic solution has a pH below 7, and a basic solution is above 7. The solutions which comprise a weak acid and a conjugate base are recognised as buffer solutions. Our body also comprises buffer systems.

There are three buffers: phosphate buffer, carbonate acid buffer, and plasma proteins buffer. An example of a carbonic buffer is blood itself. Blood contains carbonic acid H2CO3 and bicarbonate ion HCO3-1

The property of the buffer solution is to compensate for small proportions of added acid or bases. This ability to neutralise acid or bases is crucial for the reactions and processes that need particular and steady pH ranges.

Properties and Types of buffer solutions

Properties of buffer solution are: 

  • It has specific pH importance. Its pH doesn’t change even when kept for a long time.
  • On diluting the solution, its pH value doesn’t change. Also, the solution doesn’t shift by adding a little proportion of acid or base. In addition to a small proportion of acid or base, a solution that resists the pH change is a buffer solution. 

There are two types of buffer solutions: acidic buffer and basic buffer:

  • A solution with weak acid and its salts containing strong bases is called an acidic buffer solution. E.g., A solution with CH3COOH, which is weak acid and CH3COONa, which is its salt is an acidic buffer solution. 
  • A solution with a weak base and its salt-containing strong acids is called a basic buffer solution. E.g., A solution with NH4OH as a weak base and NH4CL, which is its salt, is an essential buffer solution. 

Acidic Buffer  

It has a pH lower than 7. The acidic buffer contains a weak acid and its conjugate base as salt. To change the pH of the solution, we need to alter the ratio between the acid and salt. Various acids can affect the pH in distinct ways. An example of a weak acid and its conjugate salt is acetic acid and sodium acetate.

CH3COOH → CH3COO- (aq.) + H+ (aq.)

Here, the acid equilibrium is heading towards the left. By adding sodium acetate, acetate ions will be added to the solution. According to Le Chaterlier’s Principle, the equilibrium will turn to the left. 

Think what will happen if acid is added to the acidic buffer? The buffer has to remove the H+ ions from the coming acid. Then, the acetate ions have to combine with H+ ions to form acetic acid. The reaction will eliminate Hydrogen ions since acetic acid is a weak base. This is the reason why the pH of the reaction does not change.  

Now, we will add a base to the acidic buffer. It is a bit more complicated to add a base to this buffer. The hydroxide ion of the base will react with acetic acid and form acetate ions; this will eliminate the hydroxide ions from the reaction, so we will observe no change in pH. 

Basic Buffer

Basic buffer has a pH of more than 7. The basic buffer contains a weak base and conjugate acid as a salt. A weak base and its conjugate acid is ammonia and ammonium chloride. The equilibrium is heading towards the left when we add ammonium chloride, ammonium ions will sum up to the solution. And at this instance, Le Chatelier’s principle will react to the further left side.

NH3 + H2O →NH4+ + OH- 

Let’s examine what will happen if we add acid. The added acid will release Hydrogen, and it will react with ammonia to create ammonium ions. There will be more hydroxide ions in the solution because of the interaction between ammonia and water; these hydroxide ions will react with Hydrogen to set more water. To remove the acidic presence, most of the hydroxide will be removed in this manner. Thus creating no changes in pH. 

If we add a base to the above reaction, what will happen? There will be a need to remove hydroxide ions from the incoming base. Hydroxide ions will react with ammonium ions that are in the solution. Thus, balancing pH.  

Preparation

By controlling the ratio of salt acid or salt base, we can prepare a buffer solution if association constants (pKa) of acid and (pKb) of the base are known.

Henderson-Hasselbalch Equation

Take an acid buffer solution and consider (HA) for weak acid and (KA) for its salt.

H2O + HA → H+ + A- 

Acid dissociation constant

Ka = [ (H+)(A-)] / [(H2O)]

pKa= pH – log[( salt)/(acid)] 

pH= pKa + log[(salt)/(acid)] 

the pH of acid buffer solution= pKa+[(salt)/(acid)] 

Take a basic buffer solution and consider (BA) for strong acid (B) for the weak base. 

pOH=pKb + log[(salt)/(acid)] 

pOH of basic buffer solution=pKb+ log[(salt)/(acid)] 

pOH = pKa – log[(salt)/(acid)] 

 Properties of buffer solution

Buffers are well known to avoid the changes in pH, but somehow, if any adequate proportion of strong base or acid is added, it can change. Buffer capacity is a rise in the total concentration of the particles of the buffer solution. Therefore, it has a specific pH value. 

Conclusion

Buffer refers to a solution that avoids any change in pH. Weak acid and weak bases are used for buffer solution because it does not dissociate, and the hydrogen ions will not be free. Henderson-hasselbalch equation is used to calculate the pH of the buffer solution. The human body also contains many buffers systems that help to regulate the body’s functions.