Pharmaceutical Analysis (BP102T) � UNIT II �Acid Base Titration

Acid base titration:
Theories of acid base indicators, classification of acid base titrations and theory involved in titrations of strong, weak, and very weak acids and bases, neutralization curves.

Non aqueous titration:
Solvents, acidimetry and alkalimetry titration and estimation of Sodium benzoate and Ephedrine HCl

1. Prof. Amol . S. Dighe Department of pharmaceutical Chemistry Pravara Rural College of Pharmacy, Loni Pharmaceutical Analysis (BP102T) UNIT II Acid Base Titration

2. UNIT-II Acid base titration: Theories of acid base indicators, classification of acid base titrations and theory involved in titrations of strong, weak, and very weak acids and bases, neutralization curves. Non aqueous titration: Solvents, acidimetry and alkalimetry titration and estimation of Sodium benzoate and Ephedrine HCl

3. Definition Aqueous acid base titration are usually reaction in which H3O + ions in solution is tratated against OH- ions This is applicable for titration with strong acids, strong bases, weak acids, weak bases, salt of weak acid and salt of weak base. The general reaction for any acid base titration can be represented as Such acid base titrations are carried out in standard titration conditions using an internal indicator to detect the endpoint of titration. FAQ: Explain weak acid and weak bases. Explain theories of acids and bases. Write a short note on theories of acid and bases.

4. Arrhenius theory: The concept of acid base was first described by the scientist Arrhenius in the year 1884. According to this theory Acid is a any substance when dissolved in water gives H + ions which further associated with solvent to form hydronium ion. Base can be defined as, any substance which when dissolved in water ionizes to give hydroxide ion. E.g HCl is Arrhenius acid and NaOH is Arrhenius base.

5. Advantage: It is the very first theory explaining definitions of acids and bases. It is very simple theory. It explains the nature of compound in aqueous media. Limitation: But this theory was unable to explain basicity of compound which does not contain hydroxyl ion. Another limitation of this theory is it explains acid base behavior in only aqueous media and not in non-aqueous condition. This theory defines acid and base in terms of solution only and not in solid state. This theory fail to explain the neutralization of acid and base in the absence of solvent. This theory also unable to explain acidic nature of many salts which do not contain H + in it.

6. Lowry and Bronsted theory: This Theory was proposed by scientist J. M. Lowry and J. N. Bronsted in the year 1923 individually. According to this theory Acid is a species which can donate proton and base is a species which cam accept proton. In other words, it can be stated as acid is a proton donor while base is the proton acceptor. E.g HCl is lowry-bronsted acid and water is lowry-bronsted base which can be represent as follows. Here HCl acts as acid and it donate the proton while H2O will behave as a base as it accepts proton.

7. Conjugate Acid-base pair: Consider HA as acid and B as base. Here HA acid will donate a proton to form A - as a new base known as conjugated base and similarly base B - will accept the proton to form BH the new acid known as conjugated acid. Advantage: This theory explains acid base characteristics of almost all molecules and ions which tend to either accept or donate proton. This theory can explain acid base behavior in aqueous as well as non-aqueous medium also. To explain the basic nature of compound it is not necessary to have OH- ions in it as like the necessity of Arrhenius concept. Limitation: This theory was unable to explain acid base character for non- protonic solvents e.g BF3, SO2, POCl3 there are many reaction which do not involve any proton transfer reaction, in such case this theory fails to explain the acid base character of the compound

8. Lewis theory: This theory was proposed by scientist G.N. Lewis in the year 1923. According to Lewis theory, Acid is substance which can accept a pair of electron and Lewis base is a substance which can donate a pair of electrons. Hence as per definition of acid and base , the neutralization reaction is a result of formation of a covalent or co-ordinate bond between two species.

9. Advantage: This theory explains acid base characters of species on the basis of either gain or loss of electron pair. This theory could explain acid base characters of species which do not have the ability to donate or accept proton. Limitation: Lewis acid and bases cannot be arranged in their order of strength. Through the Lewis explains the acid base concept based on the electron acceptance or donations still there are few reactions whose rate of reaction is very slow.

10. Neutralization curve FAQ: What are neutralization curve? Explain in detail neutralization curve with suitable examples. What are neutralization titration. Write a short note on neutralization curve. Give neutralization curve of strong acid and strong base with examples. Explain in detail neutralization curve with example of strong acid and strong base titration. Write a short note on neutralization curve of strong acid and strong base. Explain in detail neutralization curve with example of strong base and weak acid titration. Discuss the neutralization curve o strong acid and weak base.

11. The mechanism of neutralization process will be elaborated very clearly by studying pH changes occurred during the course of titration. The pH at which equivalent point is obtained is the most important for selection of an appropriate indicator for a titration. The pH value at the equivalence point can be calculated by plotting the titration curve with pH versus Ml of titrant added. Neutralization curve can be studied in four major type of titration , 1) Strong acid versus Strong base 2) Weak acid versus Strong base 3) weak base versus Strong acid 4) weak acid versus weak base 1) Neutralization curve for Strong acid and Strong base titration: Strong acid base titration reaction can be represent as

12. For studying titration curve can be studies in four parts 1) at initial 2) during titration 3) at equivalence point 4) after equivalence point

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15. Neutralization curve for weak acid and strong base titration: Consider the titration of acetic acid CH3COOH Vs Sodium hydroxide NaOH Here for calculation and titration 0.1 M acetic acid and 0.1 M NaOH is used. For studying titration curve can be studies in four parts 1) at initial 2) during titration 3) at equivalence point 4) after equivalence point

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18. Neutralization curve for weak base and strong acid titration: Consider the titration of ammonia Vs HCL Here for calculation and titration 0.1 M ammonia and 0.1 M HCL is used. For studying titration curve can be studies in four parts 1) at initial 2) during titration 3) at equivalence point 4) after equivalence point

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20. Neutralization curve for weak acid and weak base titration: Consider the titration of acetic acid Vs ammonia Here for calculation and titration 0.1 M Acetic Acid & 0.1 M ammonia is used. For studying titration curve can be studies in four parts 1) at initial 2) during titration 3) at equivalence point 4) after equivalence point

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22. Theories of Acid-Base Indicators FAQ: Write a short note on acid base indicators. What are Ph indicators? Discuss in brief Ostwald's theory. Explain in details universal and mixed indicators with suitable example. Discuss various theories of acid base indicators. Why phenolphthalein changes its color at end point. Give the theory involved in acid base indicators. Indicators: Indicator can be defined as a substance which exhibit color changes at particular stage of chemical reaction during titration. End point detection: The point at which complete neutralization occurs is referred as end point of titration.

23. For determining end point in the acid base titration 3 types of method can be employed. 1) Neutralization indicators 2) Mixed indicators 3) Multiple range indicators or universal indicators 1) Neutralization indicators: Neutralization indicators is the substance which exhibit different colors at various PH value Most of the indicators used in any titration are to be used in vary dilute form. Indicator which impart different colour at the end point of a titration two theories were proposed 1) Ostwald's theory 2) Resonance theory 1) Ostwald's theory: Ostwald's was the first scientist to state first theory which explains behavior of an indicator.

24. According to this theory the undissociated acidic indicators [ HIn ] and basic indicator [ InOH ] has different color than that of its ions or dissociate form. Therefore the dissociated of an acidic indicator can be written as follows. Due to this the color of solution changes which is the result of increased concentration of ionized form of an indicator.

25. Similarly we can represent dissociation of a basic indicator InOH

26. Therefore one can rewrite the equation in term of PH , This value of PH is referred as transition interval of an indicator. Commonly used indicator in acid base titration:

27. Resonance theory : All the indicator used in acid base titration are organic in nature in difference in color of compound in acidic or alkaline medium is because of the difference in the structure of two forms. 1) structure changes of phenolphthalein : According to the resonance theory phenolphthalein in the acidic condition is colorless where it is in the quinode form.

28. Ii) structure changes of azo dyes: In case of azo dyes that ie methyl orange and methyl red etc. in alkaline condition this azo dyes possesses the quinoid structure where as in acidic condition they turn into benzonoid structure.

29. 2) Mixed indicator; In same cases of titration the PH range I very narrow and colour change over this range must be very sharp. Two obtained the sharp color change at the end point in this type of titration, it is not possible use of single acid base indicator. So in order to achieve this one must use a suitable mixture of indicator which will show colour change in narrow PH range. The indicator to be used as a mixed indicator should be selected such that their dissociation constant values are close to each other. 3) Multiple range indicator or universal indicator : Multiple range indicators can be prepared by mixing more than two indicators which will be able to give the color change over the wide range of PH Universal indicators can be used for determination of approximate PH of a solution.

30. Theory involved in acid base titration The law of mass action: The law of mass action can be stated as ‘the rate of chemical reaction directly proportional to the active masses of the reacting substance.

31. Acid base equilibrium: A reversible chemical reaction is represented as follows, By applying the law of mass action , the equilibrium constant can be represented as PH: PH is nothing but the total hydrogen ion concentration of a solution which is represented and calculated as the negative logarithm of hydrogen ion concentration. Its equation can be represented as

32. Non-aqueous titration Non – aqueous titration refer to the type of titration in which the analyte is dissolved in a solvent which does not contain water. Solvent used in Non–aqueous titration: FAQ: Explain solvent in non- aqueous titration. What are the solvent used in Non–aqueous titration. Write a short note on Non–aqueous titration. Explain leveling and differentiating effects Give an account on solvent used in Non–aqueous titration . Properties of solvent used in Non–aqueous titration: Solvent used in Non–aqueous titration plays a vital role. Solvent must be in liquid state during the titration. Solvent must be non-toxic in nature.

33. Different types of solvent used in Non–aqueous titration : A solvent characteristic play an important role in case of Non–aqueous titration . Following are the main characteristics of solvent which they must possess to be used in case of Non–aqueous titration . 1) Self dissociation capability. 2) Dielectric constant. 3) Acid-base characteristics/types of solvent used 4) Leveling effects 5) Differentiating effects. 1) Self dissociation capability: Solvents can be classified into two categories based upon its dissociation capability. A) Dissociating solvents: These are the solvent which dissociated to its component ions. Example of dissociating solvent are ethanol and acetic acid.

34. A) Non-dissociating solvents: These are the solvent which non-dissociated to its component ions. Example of dissociating solvents are ether and hydrocarbon. Dissociation of solvent AB can be represented as follows.

35. 2) Dielectric constant. The dielectric constant is a measure of the extent to which a substance is polarized under an applied electrical field. This is one of the most important properties of non-aqueous solvent. The force between the two oppositely charged [articles can be given by formula In the solvents with higher d value, polar solutes get dissociated easily and completely. Higher the value D, small energy is required for separation. It will be easy to dissolve ion in solute.

36. Acid-base characteristics/types of solvent used: Solvent used in non- aqueous acid base titration can be classified into four major classes based upon its ability to donate foe accept proton. A) Aprotic solvents B) Protophilic solvents C) Protogenic solvents D) Amphiprotic solvents A) Aprotic solvents : These are solvent which are chemically neutral and are uncreative in normal condition of reaction. These solvent possess low dielectric constant and they do not cause ionization of solutes. These solvent do not undergoes reaction with acid or base. B) Protophilic solvents : These are the solvent which possess high affinity for proton. These solvents are basic in nature. E. g liquid ammonia, pyridine, ethylenediamine.

37. C) Protogenic solvents : Protogenic solvents these are the solvents which are acidic in nature and readily donate the proton. E.g anhydrous hydrofluoric acid, anhydrous sulphuric acid D) Amphiprotic solvents These are the solvents which has both capacity that is to donate a proton and to accept a proton hence the solvents have combined properties of protogenic solvent as well as protophilic solvents. E.g. alcohol and organic acids like acetic acid. Example of non-aqueous solvent: 1) Glacial acetic acid 2) Acetonitrile 3) Alcohol 4) Dioxane 5) Dimethyl formamide.

38. Disadvantage of non-aqueous titration: Non-aqueous solvents are expensive as compared to water. Most of the non-aqueous solvent are volatile and toxic in nature. Before titration removal of water is necessary, it can take water (humidity) from air Do not use a solvent until fully acquainted with its hazards and instruction for its use.

39. Types of non- aqueous titration: FAQ: Explain principles and procedure of non- aqueous titration. Add a note on preparation and standardization of 0.1 N percholric acid Based upon the nature of substance to be analyzed non- aqueous titration can be classified into to classes namely 1) Alkalimetry: The titration in which weak bases will behave as a strongly base 2) Acidimetry: The titration in which weak acid will behave as a strong acid in non- aqueous solvent.

40. 1) Alkalimetry: 1) Solvent: Glacial acetic acid is the most widely used solvent of alkalimetric titration. The main advantage of glacial acetic acid is that , it is amphiprtotic in nature. Apart from glacial acetic acid , chloroform, formic acid , propionic acid and acetonitrile can also used I phenol which will sharpen the end point. 2) Titrant; The titrant used in alkalimetric titration must be strongly acidic in nature . E.g perchoric acid, flurosulphonic acid, diphenylguanidine, 2,4 dinitrobenzene sulphonic acid, sodium carbonate 3) Indicator Used: In the titration of weak bases b using non-aqueous acid base titrations, following indicators can be used which include crystal violet, 1 naphtholbenzein,

41. Preparation and standardization of perchloric acid. Principle: Standardization of 0.1 M perchloric acid is based on non- aqueous acid base types of titration. Here potassium hydrogen phthalate is used as primary standard. It react with perchloric acid, where potassium hydrogen phthalate acts as base and perchloric acid to give phthalic acid and water. Crystal violet is used as an indicator which gives the end point as violet blue to emerald green. Procedure : A) preparation of 0.1 m perchloric acid: Mix 8.5 ml of perchloric acid with 500 ml of anhydrous glacial acid and 25 ml of acetic anhydride, cool and add sufficient anhydrous glacial acetic acid to produce 1000 ml. B) Standardization of 0.1 m perchloric acid: Weight accurately 0.35 gm of potassium hydrogen phthalate and dissolve it in 50 ml of anhydrous glacial acetic acid. Add 0.1 ml of crystal violet solution and titrate against perchloric acid Record the burette reading. Factor: Each ml of 0.1 m perchloric acid is equivalent to 0.02042 gm of C8H5KO4

42. 2) Acidimetry: 1) Solvent: The Solvents which can be used in this type of titration include ethlenendiamine, pyridine, methanol, ethanol, acetone. 2) Titrant; The titrant used in alkalimetric titration must be alkaline in nature . E.g Sodium methoxide, Lithium methoxide, potassium Methoxide 3) Indicator Used: The commonly used indicators in acidimetric titration are thymol blue, thymolphthalein, azo -violet.

43. Preparation and standardization of Lithium methoxide, Principle: Standardization lithium methoxide is based on non-aqueous acid base titration where benzoic acid act as a weak acid and it is titrated against lithium methoxide a which act as a strong base. Quinaldine red is used as an indicator which gives the end point from red to colorless. Procedure : A) preparation of 0.1 m Lithium methoxide : Dissolve small portions of 0.7 gm of freshly cut lithium metal in 150 ml of methanol and add 850 ml of toluene B) Standardization of 0.1 m Lithium methoxide : Weight accurately 0.25 gm of benzoic acid, dissolve 25 ml DMF titrated wit lithium methoxide using quinaldine red as an indicator Factor: Each ml of 0.1 M lithium methoxide is equivalent to 0.01221 gm of C6H5COOH

44. Estimation of sodium benzoate Principle: Assay of sodium benzoate is base on non-aqueous types of titration. Here sodium benzoate act as base and react with perchloric acid to give benzoic acid with the formation of potassium chloride Crystal violet is used as indicator which give end point from yellow to green Procedure: Weight accurately 0.25 gm of sodium benzoate, dissolve it in 20 ml of anhydrous glacial acetic acid titrated with perchloric acid by using crystal violet as an indicator. Factor: Each ml of 0.1 M perchloric acid is equivalent to 0.01441 gm of C7H5NaO2

45. Estimation of Ephedrine Hydrochloride Principle: Assay of ephedrine hydrochloride is base on non-aqueous types of titration. Here ephedrine hydrochloride act as base and react with perchloric acid Methyl orange is used as indicator which give end point from yellow to pink Procedure: Weight accurately 0.17 gm of ephedrine hydrochloride , dissolve it in 50 ml of acetone solution titrated with perchloric acid by using methyl orange as an indicator. Factor: Each ml of 0.1 M perchloric acid is equivalent to 0.02017 gm of C10H15NO

46. THANK Y OU