Analytical Titrations

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Titration : 

Titration Presented By :- Sachin Bobade

TOPIC’S COVERED : 

TOPIC’S COVERED 1. Introduction of titration. 2. Important terms involved in titration. 3. Classification of titration Reactions. 4. Advantages of titration. 5. Acid – Base titration and it’s Setup. 6. Standard or Volumetric Solution. 7. Eq. Point and Indicator Theory. 8. Potentiometric Titration. 9. Non-Aquase Titration.

Introduction of Titration : 

Introduction of Titration Titration is a volumetric procedure for determining the concentration of an unknown species by adding a carefully measured volume of a known species that reacts quantitatively with the solution of unknown species. The equivalence point in a titration occurs when the requirements of the balanced equation for chemical reaction are exactly satisfied. An indicator is used to find the end-point of the titration.

Important terms involved in titration : 

Important terms involved in titration 1. Titrant : The solution of known concentration added from the burette. Titrand : The solution whose concentration is to be determine usually taken in the flask. End Point : The end point is the experimental observation, at which the two solutions just completely react. It can be detected by the colour change of the Indicator. This may not be at the equivalence point

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4. Equivalence Point : The point at which the two solutions react just completely in stoichiometric proportion such that the actual theoretical completion of the reaction take place is called the equivalence point or stoichiometric end point or theoretical end point.

Classification of Titration Reactions. : 

Classification of Titration Reactions. The reactions employed in titrimetric analysis fall into two main classes. a]Those in which no change in oxidation state occurs. These are depend upon the combination of ions. b]Oxidation-reduction reaction. These involve a change of oxidation state or a transfer of electrons.

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Further divided into following categories: 1. Acid – Base titration reaction. 2. Oxidation reduction titration reaction. 3. Complexometric titration reaction. 4. Precipitation titration reaction. 5. Non-aqueous titration reaction.

Advantages of Titration : 

Titrimetirc methods are susceptible of high precision and posses several advantages with respect to Time, whenever applicable over gravimetric methods. Titrimetric methods need simpler apparatus and are quickly performed, tedious and difficult separation can be avoided. Advantages of Titration

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Reaction :- H2C2O4(aq) + 2 NaOH(aq) ---> acid base Na2C2O4(aq) + 2 H2O(liq) Carry out this reaction using a TITRATION. Acid-Base Titration.

Neutralization Titration. : 

Neutralization Titration. Neutralization: As you can see from the equations, acids release H+ into solution and bases release OH-. If we were to mix an acid and base together, the H+ ion would combine with the OH- ion to make the molecule of water: H+ (aq) + OH-(aq) H2O The neutralization reaction of an acid with a base will always produce water and a salt, as shown below: The end point is determine by Indicators shows diff. colours at diff. pH or by change in pH using pH-meter.

Classical Setup for titrating an acid with a base : 

Classical Setup for titrating an acid with a base

Instrumental Setup for titrating an acid with a base : 

Instrumental Setup for titrating an acid with a base Potentiometric Method : Potentiometer Burette (0.1N NaoH) Stirrer Reference electrode Indicator electrode Acid solution

Standard / Volumetric Solution : 

Standard / Volumetric Solution A Standard or volumetric Solution is one which contains a known weight of the reagent in a definite volume of solution. Concentration of Solution express in two ways. A) Volume Basis B) Weight Basis Formality (F) 1) Molality (m) Molarity (M) 2) Mole Fraction (x) Normality (N)

Primary Standard : 

Primary Standard A substance which is available in the pure form with definite chemical composition (equivalent wt.) is called primary Standard. eg. K-H-phthalate, succinic acid, Na-Carbonate, EDTA.

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It should satisfy the following requirements. it should have purity of very high order and the purity can established by known methods. it should be stable toward atmosphere and free from water of crystallization. It should have high eq. wt. So that wt. errors may be negligible. the reaction with the std. soln. should be stoichiometric practically instantaneous. It should be completely soluble under the employed condition.

Secondary Standard : 

Secondary Standard A secondary std. is a solution which has been previously standardized by titration with primary standard. eg. Na-thiosulphate. Oxalic acid. Cu-sulphate.

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It should satisfy the following requirements. The concentration of the solution should remain constant over long period of time. It should react rapidly wit h the analyte. The reaction with the analyte should be complete in order to obtain a sharp end point and detectable. The reaction with the analyte should be representable by a simple chemical eqn. to permit necessary calculations.

LAB PROBLEM #1: Standardize a solution of NaOH — i.e., accurately determine its concentration. : 

25.0 mL of NaOH is neutralized with 25.0 mL of 0.1 M HCl by titration to an equivalence point. What is the concentration of the NaOH? LAB PROBLEM #1: Standardize a solution of NaOH — i.e., accurately determine its concentration.

PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? : 

PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? Add water to the 3.0 M solution to lower its concentration to 0.50 M Dilute the solution! But how much water do we add?

PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? : 

PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? How much water is added? The important point is that ---> Amount of NaOH in original solution = M • V = (3.0 mol/L)(0.050 L) = 0.15 mol NaOH Amount of NaOH in final sol’n must also = 0.15 mol NaOH Volume of final solution = (0.15 mol NaOH) / (0.50 M) = 0.30 L or 300 mL

PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? : 

PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? Conclusion: add 250 mL of water to 50.0 mL of 3.0 M NaOH to make 300 mL of 0.50 M NaOH.

Preparing Solutions by Dilution : 

A shortcut M1 • V1 = M2 • V2 Preparing Solutions by Dilution

Eq. Point and Indicators : 

Eq. Point and Indicators For an acid base titration the equivalence point is the point where neutralisation occurs. Indicators posses different colours according to the [H+] concentration in the solution. Colour changes due to structural changes including the production of Quinonoid and resonance from of the indicator.

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Types of Indicator i) One colour indicator : eg. Phenolpthalein ii) Two colour indicator : eg. Methyl orange iii) Mixed Indicator : eg. Neutral red + methylene Blue at pH=7.0 ,violet-blue to green from acid to base.

Wilhelm Ostwald Theory of Indicators and Range : 

Wilhelm Ostwald Theory of Indicators and Range The colour changes shows that undissociate acid H-In or base In-OH have diff. colour from that of its ion. All indicators in general use are very weak organic acids or bases. Equation :– pH = pK In - Log [Acid form] [Base form]

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If ratio [Acid form] / [Base form] > 10, The colour of Acid form distinctly observe. If ratio [Acid form] / [Base form] < 10, The colour of Base form distinctly observe. The Colour change interval is pH = pK In ± 1 i.e. over appro. 2 pH unit i.e. Within this Range the indicator will appear to change from one colour to the other.

Acid-Base Titration Graph : 

Acid-Base Titration Graph

Properties of an indicators : 

Indicators must have the following properties : a) The indicator must change colour as close to the equivalence point with the addition of one drop of solution from the burette. b) The indicator should have high colour intensity to use in small amount. c) The first colour change should be distinct / Sharp. d) Indicator should not be effect by change in Temperature. Properties of an indicators

Colour changes of indicators : 

Colour changes of indicators

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Choosing an indicator In the strong acid titration, both indicators begin to change colour at the equivalence point (50 mL of base) so both work equally well. In the weak acid titration, thymol blue changes colour at the equivalence point, but methyl red begins to change colour after only 15mL of base are added, which is far from the equivalence point, illustrating the importance of choosing an appropriate indicator.

Potentiometric titration : 

Potentiometric titration Why :- Used to titrate colored solution where visual indicator can not work For very dilute solutions, difficult to locate exact color change Potentiometrically, equivalence point is determined accurately

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PRINCIPLE : The sudden change in milli volt at an equivalence point is the base of potentiometric titration. Eg. Titration of Cl with Silver Nitrate.

POTENTIOMETRIC TITRATIONS : 

POTENTIOMETRIC TITRATIONS PRINCIPLE :

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Graph no-1: shows the change in milli volt with ml of titrant added . Here initially milli volts slowly increases, with the addition of Silver nitrate . At the end point there is sudden rise in milli volt because of an excess drop of silver nitrate. Graph no-2: It is first derivative graph,here the difference in milli volts with each ml of titrant added is plotted against ml of titrant added. Peak of the graph is the end point of titration.

Stanadrd Electrode potential : 

Stanadrd Electrode potential Standard electrode potential, abbreviated Eo, is the measure of individual potential of a reversible electrode (at equilibrium) at standard state when:- : concentration of 1 mol : gases at a pressure of 1 bar : Temp at 25 °C. To measure the SEP of one half cell, we need an another half cell…… called as reference cell One most important reference cell is standard hydrogen electrode (SHE) electrode Metal ion solution

Reference electrode : 

Reference electrode A reference is an electrode that has the half-cell potential known, constant, and completely insensitive to the composition of the solution under study. In conjunction with this reference is the indicator or working electrode, whose response depends upon the analyte concentration.

Ideal Reference Electrode : 

Ideal Reference Electrode Is reversible and obeys the Nernst equation Exhibits a potential that is constant with time Returns to its original potential after being subjected to small currents

Standard Hydrogen Electrode : 

Standard Hydrogen Electrode

Calomel Electrode : 

Calomel Electrode

Silver/Silver Chloride Electrode : 

Silver/Silver Chloride Electrode .

End point detection : 

End point detection Due to progressively addition of titrant change in potential of Indicator electrode observed Reference electrode has constant electrode potential Near the equivalence point, a sharp change in potential is there…which is noted carefully Suppose :-ΔE = change in potential when ΔV of titrant added

Plotted graph : 

Plotted graph Graph of ΔE/ ΔV against titrant volume ΔE/ ΔV Volume of titrant End point

NON-AQUEOUS TITRATIONS : 

NON-AQUEOUS TITRATIONS Basic reason for selection of non – aqueous titration: 1.Most of the organic acids & bases are insoluble in water. 2.Most of the organic acids & bases are extremely weak. The apparent strength of an acids or bases is determined by the extent of its reaction with a solvent. In water solution all acids appears equally strong, because they react with the solvent to undergo almost complete conversion to oxonium ion & the acid anion (i.e. complete dissociation takes place) .

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Acetic acid reacts incompletely with water to form oxonium ion & there fore a weak acid in aqueous medium (i.e. incomplete dissociation in water). In contrast ,it dissolves in a base such as ethylene diamiene & reacts so completely with solvent that it behaves as a strong acid.

NON-AQUEOUS TITRATIONS : 

NON-AQUEOUS TITRATIONS Basic reason for selection of non – aqueous titration: Reaction in aqueous & non aqueous medium: HA + WATER Less oxonium ion formation (Acid ) (Less dissociation) HA + SA SAH+ + A- (Acid) (Solvent) (Oxonium ion ) (Acid anion) (More dissociation)

INDICATORS FOR NON-AQUEOUS TITRATIONS : 

INDICATORS FOR NON-AQUEOUS TITRATIONS CRYSTAL VIOLET THYMOL BLUE ORACET BLUE-B NILE BLUE

TITRANT FOR NON-AQUEOUS TITRATION : 

TITRANT FOR NON-AQUEOUS TITRATION For Basic compounds : A volumetric solution of 1. perchloric acid in Glacial acetic acid 2. Hydrochloric acid in IPA For Acidic compounds :Two classes of titrants are available. 1. Alkali metal alkoxides in IPA. 2. Tetra alkyl ammonium hydroxides in IPA.

TYPES OF NON-AQUEOUS SOLVENTS : 

TYPES OF NON-AQUEOUS SOLVENTS Depending upon their ability to donate or accept proton or not accept proton solvents are mainly classified in to four categories 1.Aprotic solvents 2.Protophilic solvents 3.Protogenic solvents 4.Amphiprotic solvents

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