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SHRI GURU RAM RAI UNIVERSITY DEHRADUN DEPARTMENT OF MSc PHARMACEUTICAL CHEMISTRY PRESENTATION ON ACID-BASE TITRATION BY PYNSHNGAINLANG KHYLLAIT MSc PHARMACEUTICAL CHEMISTRY FIRST SEMESTER.

CONTENT INTRODUCTION THEORY OF ACID AND BASE THEORY OF NEUTRALIZATION TYPE OF NEUTRALIZATION CHOICE OF INDICATOR INDICATOR THEORY EQUIVALENT POINT AND END POINT.

INTRODUCTION.

TITRATION: Tritration is a techniques where solution of known conc is use to determine the conc.of an unknown solution. TITRANT: Titrant is a known conc. Solution which is added from burrete to a known quantity analyte(unknown conc. Titrand ) until the reaction is completed. The titration process can be monitored by visual indicators,pH electrode or both. TITRAND : Is a solution of unknown concentration taken in conical flask..

ACID AND BASE TITRATION:. Acid and Base titration is a method of quantitative analysis for the determining the unknown conc. Of an Acid or a Base by the exactly neutralizing it with a standard solution of acid or base having a known conc..

ACID AND BASE THEORY. 1.Arrhenius theory 2. Bronsted-Lowry theory 3. Lewis theory ARRHENIUS THEORY: Those substance which give H+ ions when dissolve in water are called acid e.g , HCl,H2SO4 Those substance which produce OH - Ions when dissolve in water e.g , NaOH, Ca(OH) 2.

BRONSTED-LOWRY THEORY: Also called proton theory of acid and base Bronsted-Lowry theory state that any compound that can transfer a proton(H) to any other compound is an acid and the compound that accepts the proton(H) is a base. e.g , HCL + NH3= NH4 +Cl They also state that when an acid loses a proton (H) it form a base,called a conjugate base of an acid,when a basic substance gain a proton,it form an acid its called as the conjugate acid of a base e.g , NH3 +HCl =NH4 +CL In the above equation ammonium ion (NH4) is the conjugate acid of a base NH3 and Cl ion is a conjugate base of hydrochloric(HCl) acid..

LEWIS THEORY: . Acid are compounds that can accept a pair of electrons. Base are compound that can donate a pair of electrons. e.g , BF3 + F =BF4.

THEORY OF NEUTRALIZATION. NEUTRALIZATION REACTION: A neutralization reaction reaction is a reaction when an acid and base react to form salt and water which is involve the combination oh H+ ion and OH- ions to generate water NEUTRALIZATION CURVE: Is a plot of pH against the volume of alkali added(ml) TYPE OF NEUTRALIZATION REACTION: Strong acid and strong base. Strong acid and weak base. Strong base and weak acid. Weak acid and weak base..

TITRATION CURVES 14 12 10 8 6 4 2 o o 12 10 8 6 4 2 o Equivalence point s 10 20 25 30 35 40 45 so Vokjrne of 0.1 mol cimo base ( Strong acid and strong base ) Equivalence point 14 12 10 8 6 4 2 2 o 10 8 6 4 2 o o s 10 15 20 25 30 3S 40 45 Vok•rne of O. 1 rnol drn-3 base ( Weak acid and weak base ) SO o Equivalence point S to 20 25 30 3S 40 4S SO Volume of O. dm• base added/crn• ( Strong acid and weak base ) Equivalence point S 10 IS 20 2S 30 3S 40 4S SO Volume Of O. dm• base added/crn» ( Weak acid and strong base ).

CHOICE OF INDICATORS. When selecting an indicator for an acid – base titrations, choose an indicator whose pH range falls within the pH change of reaction e.g , In the titration of strong acid and strong base the pH quickly changes from 3 to 11. The indicator phenolphthalein whose range spans from 8 to 10 therefore makes a good choice for this type of titration. e.g , suppose the reaction between analyte and reagent is just complete(equivalence point reached) when 20ml reagent solution is added,if the indicator use for this titration show a colour change when 20.1ml reagent solution has benn added then there is a difference of 0.1ml in the equivalent point and the actual end point then this difference is called as the indicator error..

THEORY OF INDICATORS. An indicator is a substance which is used to determine the end point in a titration. In acid – base titrations , organic substances(weak acids or weak bases) are generally used as indicators. They change their colour within a certain pH range..

Oswald’s Theory: The colour change due to the ionization of the acid – base indicator Phenolphthalein : It can be represent as Hph . It ionized in solution to a small extent as Hph = H+ + ph - Colourless pink Methyl orange: It is a very weak base and can be represent as MeOH. It is ionized in a solution to give Me+ and OH- ions. MeOH = Me+ + OH Yellow Red.

Quinonoid Theory : - Acid – Base indicators exists in two tautomeric forms having different structures which are in equilibrium. One form is term as benzenoid form and the other Quinonoid form. The two form have different colors. The colour change in due to the interconversation of one tautomeric form into other. One form mainly exist in acidic medium and other in alkaline medium Phenolphthalein: Has benzenoid form in acidic medium and thus it is colourless while it has Quinonoid form in alkaline medium which has pink colour.

Methyl Orange : Has Quinonoid form in acidic solution and benzonoid in alkaline solution. The colour of benzonoid form is yellow while that of Quinonoid form is red..

EQUIVALENCE POINT AND END POINT. EQUIVALENCE POINT: Equivalent point is the point at which chemically equivalent quantities of the reactant have been mixed completely END POINT: End point is the point at which the indicator change its colors or in other word end point of any titration is come after equivalent point..