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Basic Buffer Solution - Definition, Henderson-Hasselbalch Equation for Basic Buffer, Buffer Capacity

You might have heard ‘Buffer zone’. But what is a buffer? And what is it to do with chemistry?

Buffer represents unaffected by changes. Let us consider two bicycles, one with a shocker (green) and the other without a shocker (red). When a stone comes in the way of the tire, the bicycle having a shocker (the green one) resists the jerk, while the one with no shocker (the red one) experiences more jerk. The jerk experienced by the bicycler is shown by white highlights along his spine. 

Buffer solutions are similar to the bicycle with the shocker. Just like the bicycle with the shocker resists the jerk, buffer solutions resist the change in pH in the addition of an acid or base.

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Table of Content

What is a Basic Buffer Solution?

Basic buffer is prepared by mixing a weak base and its salt with a strong acid

Weak Base Strong Acid Buffer (WB+Salt of WBSA)

How pH change is resisted by a basic buffer solution?

Consider a basic buffer containing a weak base , and its salt, .

dissociates completely and increases the concentration of in the reaction which means according to Le Chatelier's principle, the equilibrium of the ionization of the weak base shifts backwards. Now dissociation of is suppressed and the concentration of decreases due to the presence of a common ion . This is known as the common ion effect.

 Case-1: If we add a small amount of to the solution, it reacts with the  ions and is removed as . There is less change in the pH of the solution or we can say that it is a buffer solution.

 Case-2: If we add a small amount of in the solution, then it combines with and is removed as . However, further dissociates into & to maintain equilibrium.

calculation of Basic Buffer

Buffer is an aqueous solution containing a mixture of a weak acid/base and its salt with strong base/acid. Buffering action of the solution depends on the concentration of relative ratio of acid/base and their salts. 

Consider a buffer solution consisting of a weak base () having concentration dissociating with the degree of dissociation and its salt with strong base () having concentration

       

Initial concentration (t=0)                                               0                             0

Concentration at                                                                   

equilibrium (t=)    

As the dissociation of is suppressed due to the common ion effect, such that .

Hence,

of the weak base can be written as:

This equation is called the Henderson-Hasselbalch equation.

Buffer Capacity

The number of moles of acid or base to be added to 1 L of buffer solution to change the pH by one unit is the Buffer capacity of the buffer.

Βuffer Capacity =

Maximum Buffer Capacity

When the proportions of acid (or base) and anion (or cation) from the salt are the same, i.e., [Acid] = [Anion of salt] and [Base] = [Cation of salt], a buffer has the maximum buffer capacity. 

As a result, (or ) at this moment, according to the Henderson Hasselbalch equation.

Related video links: Discussion on Buffer Solution, Salt Hydrolysis, Solubility Product - Class 11 Chemistry|JEE

Practice Problems

Q1. What are the possible ways by which we can basic buffer solutions?

Answer. Method - 1: Mixing  a weak base and salt of that weak base with a strong acid

Method - 2: By mixing a salt solution of a weak base with a lesser amount of a strong base solution,

For example, and

                                               

Initial moles                          1 mole             0.5 moles                            0                       0

Final moles                         0.5 moles                    0                             0.5 moles        0.5 moles

Method - 3: By mixing a weak base solution with a lesser amount of a strong acid solution, 

For example,  and

                                               

Initial moles                          1 mole             0.5 moles                            0                      

Final moles                         0.5 moles                    0                             0.5 moles       

Q2. The effective range for of Basic buffer & lies between x and y. What is the value of y-x if for is 9.26?

Answer. The for a buffer solution lies between &

Hence,

Q3. Select the pair(s) of solutions that form a basic buffer upon mixing.

Answer. 

  1. &
  2. &
  3. &
  4. and

A weak base and its salt are combined with a strong acid to make a basic buffer solution.

  1. & Both are acids.
  2. is a weak base and is a salt of a weak acid and strong base 
  3. is a strong acid and is a salt of a weak acid and strong base. 
  4. is a weak base and is a salt of strong acid and weak base .

Hence the correct option is (D).

Q4. What is the ratio of conjugate acid and base in the given two conditions

Answer. 

 

Condition (1);

 

=1:1

Condition (2);

 

=10:1

Frequently Asked Questions - FAQ

Question 1. Any example that relates to the use of buffer solutions in daily life?

Answer. An example of the use of buffers in pH regulation is the use of bicarbonate and carbonic acid buffer systems to regulate the pH of animal blood.

Question 2. Name a universal buffer that can be used for a large pH range?

Answer. Britton Robinson Buffer known as Universal Buffer is used for a large range of pH from 2 to 12.

Question 3. Is there any preservation required for buffer solutions or are they stable for years?

Answer. Buffers act as media for bacterial growth. So, we need to add buffer preservatives which act as antifungal and antibacterial agents.

Question 4. Instead of having chemicals, why do lipsticks not decay the lips?

Answer. Lipsticks do not decay the lips because they contain buffering agents in them which adjust the pH of the lipstick concerning lips.

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Related topics

Buffer Solution- Acidic Buffer Salt Hydrolysis- Salt of a weak acid and strong base
Salt Hydrolysis- Salt of a weak acid and weak base Salt Hydrolysis- Salt of strong acid and weak base
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