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Acidic Buffer Solution - Definition, Henderson-Hasselbalch Equation for Acidic Buffer, Applications of Buffer, Practice Problems and FAQs

Acidic Buffer Solution - Definition, Henderson-Hasselbalch Equation for Acidic Buffer, Applications of Buffer, Practice Problems and FAQs

Have you ever experienced a situation, where any changes you are making on a system are not being observed? You have seen a person walking and running on a treadmill. Does the person move even an inch forward? The person’s forward movement is nullified by the backward movement of the treadmill.

The buffer solution also exhibits a similar situation. Any addition or increase in small Hydrogen ion or hydroxide concentration (pH) in solution is more or less neutralized by a buffer action, so that solution pH is nearly maintained at the original level. 

image

A person walking and running on a treadmill.

Table of Content

What is an Acidic Buffer Solution?

The buffer solution is a solution that can maintain nearly the same pH on either dilution or the addition of a small amount of either acid or base.

On the addition of a small amount of HCl acid.

  • to a non-buffer solution, the pH changes from 8 to 5, whereas
  • in a buffer solution, the pH only changes marginally from 8 to 7.8. 

image2

Non-buffer solution

image3

Buffer solution

Acidic buffer is an aqueous solution containing a weak acid and its salt with a strong base

Weak Acid (WA) Strong Base (SB) Buffer (WA+Salt of WASB)

How pH change is resisted by an acidic buffer solution?

Consider an acidic buffer containing a weak acid, and its salt, .

Common Ion effect: Being a strong electrolyte 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 acid shifts backwards. Hence, dissociation of is 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 acetate ions and is removed as undissociated . There is no 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 to the solution, it combines with and is removed as neutral . However, further dissociates into and to maintain equilibrium.

calculation of Acidic 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 acid () having concentration dissociating with the degree of dissociation and its salt with a strong base () having concentration .

Initial concentration (t=0)                                                   0                             0 

Concentration at                                                                     

equilibrium (t=)        

The dissociation of a weak acid, is suppressed due to the common ion effect, such that .

Hence,

of a weak acid can be written as:

    

This equation is called the Henderson-Hasselbalch equation. 

This equation is great for selecting buffer solution, calculating the pH of a buffer solution and determining the relative ratio of concentrations required for the preparation of a particular pH.

Applications of Buffer

1. In industrial processes: It's utilized in electroplating and the leather industry, for example. The texture and colour of the completed product in the leather industry are determined by a narrow range of pH control of tanning and dyeing baths. 

Some alloys can only be electroplated provided a very stringent pH control is maintained. As a result, buffers are used.

2. In biological processes: The pH of our blood remains constant at about 7.4. The buffer action in

the blood is due to and ions. They are in equilibrium according to the following acid-

base reaction:

When an acidic substance enters the blood, hydronium ion combines with bicarbonate ion to

give carbonic acid and water. When a basic substance enters the blood, combines with

carbonic acid to give bicarbonate ions and water.

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

Practice Problems

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

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

Method - 2: By mixing a salt solution of a weak acid with a small amount of the corresponding strong acid.

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 acid solution with a lesser amount of a strong base.

For example and

                                               

Initial moles                          1 mole             0.5 moles                            0                      

Final moles                         0.5 moles                    0                             0.5 moles     

Q2. 200 mL of 0.02 M CH3COOH and 400 mL of 0.04 M make up a buffer solution. Water (700 mL) is added. (=4.74) Calculate the pH of the solution before and after dilution.

Answer. After mixing,  =

After dilution, total volume =1000 mL

=

[

before and after dilution are 5.34 and 5.34

Q3. Which mixture represent Acidic buffer solution:

  1.  

Answer. An acidic Buffer solution is a mixture of a weak acid and its salt with a strong base

  1.  is a strong acid and is salt of strong acid and strong base
  2. is a weak acid and is salt of a weak acid and strong base 
  3. is a weak acid and is a salt of strong acid and strong base
  4. is a weak base and is a salt of strong acid and strong base

Hence the correct option is (B).

Q4. An acidic buffer can be obtained by mixing:

  1. 50 mL of 0.2 M and 200 mL of 0.1 M
  2.  200 mL of 0.05 M and 400 mL of 0.05 M
  3.  50 mL of 0.2 M and 50 mL of 0.2 M
  4.  100 mL of 0.1 M and 400 mL of 0.05 M     

Answer.

(A)                                                        

Initial moles                          20 mmoles    10 mmoles                   0

Final moles                            10 mmoles             0                        10 mmoles         10 mmoles

(B); In an acidic buffer, acid should be weak. HCl is a strong acid. Hence, incorrect

(C);                                                       

Initial moles                          1 mole               1 mole                                              0                      

Final moles                                 0                           0                             1 mole             

(D);                                                       

Initial moles                          1 mole              2 moles                            0                      

Final moles                                 0                     1mole                                        1 mole             

In option (A), After the reaction, There is a weak acid and salt of a weak acid and strong base is present. So. This is an acidic buffer.

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. Why are buffers used in the production of alcohol?

Answer. Buffers are used in the production of alcohol because they maintain the pH at specific levels and inhibit the acidity which can ruin the catalytic enzymes needed for the formation of the product.

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

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

Question 4. Is a buffer solution always neutral in nature?

Answer. Buffer means constant pH It can be anything between 0-14, though it is used for specific equilibrium reactions of use. So, we can say that the Buffer solution is not neutral by nature. It just maintains the pH of the solution.

Related topics

Buffer Solution- Basic 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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