Buffer capacity

These slide contains all about Buffer capacity.
Factors affecting Buffer Capacity.
For more info contact:[email protected]

1. Buffer Capacity Presented By:- Mr.Rushikesh Laxman Tamhane

2. Buffer Capacity Definition :- The amount of an acid or base that can be added to a 1 Liter of a buffer solution before its pH changes significantly. OR Maximum amount of either strong acid or strong base that can be added before a significant change in the pH occurs. It is indicated by the term Buffer index (β). It is also known as Buffer Value or Buffer Efficiency. Mathematically buffer capacity is expressed as: β =  B/  pH……(Equation no.1) Where, ΔB=Amount of acid or base added to change the pH By 1 unit ΔpH = Change in pH

3. Buffer Capacity The Buffer capacity depends upon two factors Ratio of the salt to the acid or base Total Buffer Concentration The relation between Buffer capacity and Buffer Concentration is Given By Koppel, Spiro and Van Slyke Equation:- β = 2.3C Ka[H 3 O] Ka+[H 3 O + ] Where, C= Total buffer concentration (Sum of Molar concentration of acid and Salt) Buffer Capacity is not a fixed value. It depends upon amount of base added. For most of pharmaceutical solutions,Buffers ranging from 0.01-0.1 are usually adequate. Buffer Capacity must be high enough to maintain the duration of product for long time. But in case of Ophthalmic & Parental Product the Buffer Capacity should be low.

4. Buffer Capacity Maximum Buffer Capacity:- Maximum Buffer capacity occur when pH=pKa or [H 3 O + ]=Ka Β max = 2.303C [H 3 O + ] 2 / [2(H 3 O + )] 2 Β max = 2.303C/4 Β max = 0.576 C …..Eq.2 For example, when 0.03 mole of sodium hydroxide is added to 0.1 M acetate buffer system the pH increases from 4.76 to 5.03 with a change of 0.27 pH units,

5. Factors Affecting Buffer Capacity Ratio of [A−]/[HA] Total Buffer Concentration: Temperature Ionic Strength:

6. Factors Affecting Buffer Capacity Ratio of [A−]/[HA] / Ratio of the salt to the acid or base.:- The actual concentration of salt to the acid or base effects the buffer.This ratio should be 1:1 at this stage pH is considered as optimal. The more is the Salt and Acid or Basic molecules present in solution less is the effect of acid or base addition on pH of solution. Consider the addition of HCl to the reaction in which there are Initially Greater no of salt and acid molecule present A − + HCl HA + Cl − This changes the pH but very slowly due to presence of high amount of salt ..After continue addition of HCl The point will come at which Salt get destroyed and HCl will donate electron directly to H 2 O HCl + H2O H3O+ + Cl− This point is Called as Breaking of Buffer Solution.

7. Factors Affecting Buffer Capacity Total Buffer Concentration: Buffer capacity depends upon concentration of the buffer. For example for 0.5 M Buffer it will require more acid and base as compared to 0.05 M. The relationship between buffer capacity and buffer concentration is given by:- β = 2.3C Ka[H 3 O] Ka+[H 3 O + ] A buffer solution containing a weak acid and its salt has a maximum buffer capacity (βmax) when pH = pKa Hence Maximum buffer capacity is given by Equation no.2 which is Β max = 0.576 C

8. Factors Affecting Buffer Capacity Temperature:- The pH values are dependent on temperature. Buffers are required to be maintained at constant temperature. Any change in temperature of the buffer results in reduction in effectiveness of the buffer. Buffer containing base and its salt found to show greater changes in buffer capacity with temperature. Effect of temperature on the pH is given below:-

9. Factors Affecting Buffer Capacity Ionic Strength: Ionic strength is reduced by dilution. Change in ionic strength changes the pH of buffer solution resulting in decreased buffer capacity. So, whenever pH of buffer solution is mentioned ionic strength should be specified.