buffers

Question 1

buffers

Answer 1

 Buffers are compounds or mixture of compounds that by their presence in their solution resists change
in pH upon the addition of small quantities of acid or alkali. The resistance to a change in pH is known
as buffer action.
 The substances used to produce buffer action are called buffers and usually consists of mixture of:
o Type “A”: A weak acid and its conjugate base that is a salt
o Type “B”: A weak base and a conjugate acid

Question 2

types of buffer solutio

Answer 2

On the basis of constituents of buffer solution, the buffer solution can be grouped into two types:
1. Acidic Buffers
2. Basic Buffers

Question 3

acidic buffers

Answer 3

1. ACIDIC BUFFER: Those buffer solutions, which are prepared by mixing a weak acid with its salt with
   strong base e.g. CH3COOH / CH3COONa, H2CO3 / Na2CO3 etc.

Question 4

basic buffers

Answer 4

2. BASIC BUFFER: These are buffer solution which are formed by mixing base with its salt with strong
   acid e.g. NH4OH / NH4Cl & ephedrine / ephedrine HCl, etc.

Question 5

mechanism

Answer 5

The resistance, which is offered to the change in pH of buffer solution is said to be buffer action or
mechanism of buffer solution.
As an acidic buffer has weak acid & salt of strong base, so buffer solution contains an acidic species
which react with base added to the solution & a basic species which react with incoming acid in order to
maintain pH of buffer solution. And this whole process reversed in case of basic buffer.
For example, buffer solution CH3COOH / CH3COONa has acidic species H3O

+ & basic species

CH3COOH. When a basic species (e.g. OH-

) is added to this buffer solution. CH3COOH react with it &

neutralizes it. And in the same way if acidic species (e.g. H3O
+

) is added to this buffer solution, the CH3COO-
react with it & neutralizes it.

CH3COOH → CH3COO
− + H
+
CH3COONa → CH3COO
− + Na+

Question 6

common ion effect type A

Answer 6

 This expression is developed by considering the effect of a salt on the ionization of a weak acid when
the salt and acid has a common ion e.g. when sodium acetate is added to acetic acid, the dissociation
constant for a weak acid is:
Ka =
[Ac−][H3O
+]
[HAc]

= 1.75 × 10−5

distributed due to the acetate ion supplied by the salt. Hence in order to maintain the constant 1.75 ×
10-5
, the hydrogen ion in nominator will decrease and the HAc in demoniatior increases. So that the constant
Ka remains unaltered and the equilibrium is subjected towards the reactants. The ionization of acetic acid is
represented:

HAc + H2O ⟶ Ac− + H3O
+

by the addition of common ion Ac-

. This is an example of common ion effect.

The pH of the final solution is obtained by arranging the equilibrium equation of dissociation constant.

[H3O
+] =
Ka [HAc]
[Ac−]

If the acid is weak and ionized only slightly then the expression HAc may be considered to represent
the total concentration and it may be simply written as acid in a slightly ionize acetic solution. The Acion
only comes from the salt that is sodium acetate since one mole of sodium acetate yields one mole of acetate
ion. The total concentration of Acion may be replaced by the term salt.

[H3O
+] =
Ka [Acid]
[Salt]

Equation may be expressed in term of log,

− log [H3O] = − logKa – log [Acid] + log [Salt]

From this buffer equation is obtained for weak acid and its salt,

pH = pKa + log
[Salt]
[Acid]
This equation can give you calculation in range of 4 – 10 pH.

Question 7

type B

Answer 7

Buffer solution of weak bases and their salts are ordinarily not prepared because of volatility and
instability of the base and secondly because of the dependence of pH on pKw which is often affected by
temperature change e.g. ephedrine and ephedrine HCl is often used in pharmaceutical solution as buffer. Their
buffer equation can also derive analogous to deserve weak acid buffer.

[OH−] =
Kb [Base]
[Salt]
[OH−] =
Kw
[H3O−]

Comparing both equations we get,
Kw
[H3O−]
=
Kb [Base]
[Salt]
pH = pKw – pKb + log
[Base]
[Salt]

Question 8

conclusions

Answer 8

 The strength of an acid can be expressed in terms of either Ka or the Kb if its conjugate base is known.
 The Ka of an acid can be calculated if the Kb of its conjugate base is known.
 The stronger an acid is, the weaker is its conjugate base and vice versa.

Question 9

factors affecting pH

Answer 9

There are some factors which influence the pH of buffer solution. Among these factors some are as
follows:
1. NEUTRAL SALT: By the addition of small quantity of neutral salt, there is no effect on the pH of the
buffer solution. But when the concentration of added neutral salt is increased, then pH of buffer solution
changes due to change in ionic strength.
2. DILUTION: Dilution of buffer solution i.e. the addition of H2O in moderate quantities may not change
pH but can cause small positive or negative deviation because it can act as weak acid or base.
3. TEMPERATURE: The pH of acetate buffers increases with temperature whereas pH of boric acid and
sodium borate buffer decreases with increase in temperature and basic buffers are more effected by change in
temperature.

Question 10

buffer capacity

Answer 10

 The magnitude of a resistance of a buffer to pH change is reffered as buffer capacity β.
 It is also called buffer efficiency, buffer index and buffer value.
 It is the ratio of the increment of strong base (or acid) to the small change in pH brought by this
addition.

β =
∆B
∆pH

 Δ β is the small increment in gram equivalent per liter of strong base added to a buffer solution to
produce a pH change of ΔpH.
 According to equation, the buffer capacity has a value of one when one gram equivalent of base
produce a pH change of 1 in one-liter buffer solution.

Question 11

maximum buffer capacity

Answer 11

The capacity of a solution will be maximum, when salt to acid ratio of buffer solution is one (i.e. pH
= pKa). According to buffer equation:

pH = pKa + log
[Salt]
[Acid]

If [salt] = [acid]

pH = pKa + log 1
pH = pKa + 0
pH = pKa

Question 12

biological buffers

Answer 12

The buffer which are present in different biological systems are called Biological or In-vivo buffers.
Biological buffers are classified into two groups:
1-primary
2-secondar

Question 13

primary buffers

Answer 13

 These buffers help in maintaining the pH of the blood. The normal value blood pH is 7.4. If it exceeds
8 alkalosis & if lower than 7 acidosis is resulted.
 These are the buffers which are present in human blood plasma. Plasma has three types of buffer
systems.
o Carbonic acid & its salt i.e. H2CO3 / NaNCO3
o Phosphoric acid & its salt i.e. H3PO4 / Na3PO4
o Plasma protein in acts as acid & salt is formed. This resultant salt & uncombined protein forms
a system, which acts as buffer.

Question 14

secondary buffers

Answer 14

 The buffers are present in the RBC’s or erythrocytes are called secondary buffer. Following are some
examples of secondary buffers.
o Hemoglobin & oxy – hemoglobin (oxidizing buffer)
o Phosphoric acid & potassium salt of phosphoric acid.

Question 15

buffers in pharmaceutical and in biological systems

Answer 15

 Blood is maintained at a pH of about 7.4 by 8.0 called primary buffers in erythrocytes. The plasma
contains carbonic acid/ bicarbonates and acid/alkali Na salts of H3PO4 as buffers. Plasma proteins
which behave as acid in blood can combine with bases and so act as buffers. In erythrocytes two buffer
systems consist of hemoglobin / oxhemoglobin and acid/alkali K salts of H3PO4. When the pH of
blood goes 7 or above 7.8 Life is in serious danger. The pH of blood in diabetic coma is alleged to
drop as low as 6.8. Lacrimal fluids or tears have pH of 7.4. They have a high dilution value of 1:15
with neutral distilled water before an alternation in pH is noticed.

Question 16

drug as buffer

Answer 16

The solutions of drugs are usually weak electrolytes, so they act as buffers in their own fashion.
EXPLANATION:
When salicylic acid is kept in glass bottle, the ions (e.g. Na+

) reached out from walls & react with
salicylic acid to form the conjugate base or salt (e.g. sodium salicylate). The salicylic acid & resulting salt
from a buffer which resists the change in pH of the salicylic acid.
Another example is of ephedrine (base). When HCl is added to its solution, ephedrine HCl is formed
which is conjugate acid or salt of ephedrine. So both forming buffer and so stable the pH of the drug.

Question 17

pharmaceutical buffers

Answer 17

The buffer action of drugs is very small, which only maintains the pH drug by the addition of
atmospheric CO2 or ions of glass. So far the stability of drugs, same additional buffer is used known as
pharmaceutical Buffers. Some familiar examples of pharmaceutical buffers are as follows:
1-gifford
2-sorensen
3-palitzshh
4-clark-lubs buffer

Question 18

gifford buffer

Answer 18

1. Gifford Buffer: [H3BO3 + NaCO3– H2O] → 9
   This buffer solution is formed by mixing the solution of boric acid with solution of Monohydrated
   sodium carbonate and it is used in pH b/w 5→ 9.

Question 19

sorenson buffer

Answer 19

2. Sorensen Buffer: [Na3PO4] 6 → 9
   This buffer solution is obtained by mixing salts of sodium phosphate (Na3PO4). It is used in the pH
   range from 6 to 8. NaCl is also added in order to make the buffer isotonic with body fluid.

Question 20

palitzsh

Answer 20

3. Palitzsch Buffer: [H3BO3 + Na3BO3] + NaCl; 7 →9
   This buffer is obtained by mixing the solutions of boric acid & sodium borate. In this buffer, NaCl is
   added in order to make the solution isotonic with body fluid. It is used for ophthalmic solutions in the pH
   range of 7 to 9.

Question 21

clark-lub buffer

Answer 21

4. Clark-Lubs Buffers:
5. HCl and KCl pH; 1.2 – 2.2
6. HCl and K-Hydrogen Phthalate pH; 2.2 – 4.0
7. NaOH and K-Hydrogen Phthalate pH; 4.2 – 5.8
8. NaOH and KH2PO4 pH; 5.8 – 8.0
9. H3BO3, NaCl and KCl pH; 8.0 – 10.0

Question 22

preparation of pharmaceutical buffer

Answer 22

In order to prepare a pharmaceutical buffer, following steps are very important & to be known by the
pharmacist.
1. For maximum buffer capacity, weak acid having PK a value equal to pH (of required solution) is used
in the formation of pharmaceutical buffers.
2. In order to get required pH for buffer, the ratio of salt & weak acid is determined by buffer equation.
It should be in the range of 4.0 → 10.0.
3. The acid and salt used for the preparation of buffer solution should be 0.05 → 0.5 molar & final buffer
solution with buffer capacity 0.01 → 0.1 is best.
4. Other important factors for the preparation of pharmaceutical buffer are:
a. Availability of chemicals
b. Sterility of final solution
c. Stability of drugs & buffer with time
d. Freedom from toxicity
e. Cost of materials
5. Final step is the determination of P H & buffer capacity of final product. It may be different from
calculated value because of activity coefficient of different chemicals used.

Question 23

buffered isotonic solution

Answer 23

 In addition to pH adjustment pharmaceutical solution should also have same osmotic pressure so that
of the body fluids. Isotonic solutions cause no swelling or contraction of tissue with which they come
in contact. It can be demonstrated by mixing as small quantity of blood with aqueous sodium chloride
solution with different toxicity (NaCl → 0.9g/100 ml ) is considered to be isotonic and other solution
containing higher is considered hypertonic and less than 0.9g is considered hypertonic 2.0% boric acid
solution is iso-osmotic with blood but can also pass through cell membrane easily.
 Therefore, a solution containing a drug calculated to be isosmotic with blood is isotonic only when the
blood is isotonic only when the blood cells are impermeable to solvent only.
 Mucous lining of eye act as true semipermeable membrane which does not allow toxic acid to cross.

Question 24

measurment of toxicity

Answer 24

 The toxicity of solutions may be determined by one of two methods.
 First is the hemolytic method in which the effect of various solution of drug is observed on the
appearance of red blood cells suspended in the solution.
 Second approach used to measure toxicity is based on any of the methods that determine colligative
properties. The most important are:
o White Vincent Method
o The Sprowls Method

Question 25

aplication of of pharmaceutical bufffers

Answer 25

1. SHICK TEST TOXIN: It is an immune diagnostic test for diphtheria. A dilution of diphtheria toxin is a
   dose of defined potency. A dilution prepared with isotonic buffer solution retains its potency for two months
   at 250C. A mixture of borax boric acid / NaCl is used in isotonic buffer solution.
2. IMPROVING PURITY: Proteins are purified depends on the fact that amphoteric compounds are slightly
   soluble at their isoelectric point. For example, insulin precipitates from the aqueous solution in the pH range
   of 5 to 6. This technique is used for insulin purification.
3. INCREASED STABILITY: Because of hydrolysis, many compounds are unstable in aqueous solutions.
   These solutions can be stabilized by regulating the pH. For example, the stability of vitamins is within a narrow
   range of pH only.
4. ENHANCED SOLUBILITY: If the pH of the solution is not properly maintained, then the drug
   dissolution can precipitate. This principle applies in the dosage forms manufacturing, and some
   pharmaceutical ingredients and drugs dissolve only at specific pH, hence, it is necessary to maintain the right
   pH of the solution.
5. OPTIMIZING BIOLOGICAL ACTIVITY: Enzymes contain most activity only on certain pH values.
   For example, at pH 1.5, there is a maximum activity of pepsin.
6. CULTURE MEDIA OF MICROORGANISMS: The preparation of microbial culture is of great
   importance in modern drug manufacturing. Microorganisms can grow only in optimum conditions of a definite
   pH range. So basic salts are used to maintain the pH of the culture at a specific range.
7. TISSUE CULTURE LABS: To keep the tissue cultures in-vitro, the pH of the system must be constant so
   that tissues may not be spoiled.