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Titrimetric methods
- 2. Terms Used Titrant • Solution in burette Titrand • Solution in conical flask Titration • The process in which small amount of titrant is added to titrand till the reaction goes to completion End point • The completion of reaction is shown by colour change of indicator •The point when amount of titrant is added is chemically equivalent to amount of substance titrated •The difference between equivalence point and end point • It is a substance which indicates the completion of reaction of titration by colour change Indicator Titrimetric methods 2
- 3. Standard Solution A known volume of solution is made to react with another solution and volume required for completion of reaction is measured. Knowing the concentration of one of the solution other can be calculated. Process of adding solution from burette to conical flask till completion of reaction and determining the determining the quantity Reaction should be complete and proceed only in forward direction Equilibrium constant should be very high Reaction should e rapid, simple instantaneous ,stoichiometric, It should be possible to represent the reaction with the help of a balanced equation . An appropriate indicator should be available to detect the end point either by colour change ,turbidity ,fluorescence Suitable condition for titrimetry A solution of known concentration.Standard solution is taken in burette Titrimetry Titrimetric methods 3
- 4. Complexo metric Titration Neutralisation titration Redox Titration Acidimetry /Alkalimetry Concentration of H+ ions changes rapidly at the end point The indicators are weak acids or bases which changes the colour due to change in concentration of H+ions Transfer of electrons between titrant and titrand One of the species is reduced and other gets oxidised Potential of the system changes at end point so substances which can change the colour Due to change in potential are used and called as Redox indicators Metal forms complex with indicator when complexing agent is added this M-In complex breaks and Metal ligand complex is formed. colour of free indicator is observed at end point. Indicators are called Metallochromic indicators Titrimetric methods 4
- 5. Precipitation titration Iodimetric titration Iodometric Titration Reactants react to form at least one sparingly soluble product One of the product is sparingly soluble halides with Silver nitrate Free iodine is used to titrate with a reducing agent. Direct method. Quantify reducing agents. Species is directly titrated with iodide solution and then released iodine is titrated with thiosulphate. Indirect method .Quantify oxidizing agent Titrimetric methods 5
- 6. H+Cl- Na+OH- At equivalence pointBefore end point H+Cl- Na+OH- Na+ OH- NaCl+ H2O OH- Na+ OH- Neutralisation titration H2O NaCl + H2O NaCl + H2OH+ H+H+ OH- At end point Indicators Acid Colour Basic colour Methyl orange red yellow Phenolphthalein No clour PinkTitrimetric methods 6
- 7. CuSO4 +KI->I 2 Before Start of titration Iodometric titration Na2S2O3 I2 Na2S2O3+ I 2 Na2S4O6,NaI During process of titration CuSO4 +KI->I 2 Iodimetric titration Reducing agent Indicators With iodine No iodine Starch Blue colourless Iodine directly titrated with reducing solution Direct ,Iodine gets reduced One redox reaction Analyte + I - I2 I2 + Titrant-> Product Indirect ,Iodine gets oxidised first and then reduced by reducing agent Two redox reactions occur Titrimetric methods 7
- 8. AgCl Ag+ AgCl Cl- Cl- Cl- M+Cl- Ag+ NO3 Ag+ After end pointBefore end point negatively charged AgCl Ag+ Ag+ NO3 NO3 NO3 M+ AgCl Ag+ Ag+ AgCl Ag+ Ag+ NO3 F- F- F- F- Pink Precipitation titration Indicators No adsorption After adsorption Fluorescein yellow Pink Titrimetric methods 8
- 9. M n+ Before Start of titration M-In Complexometric titration Complexing agent Indicator In M-In M-In ML In M-L In Complexing agent During process of titration At end point Indicators Free Complexed pH Erio-chrome Black T Blue Wine red 6-7 Titrimetric methods 9
- 10. Reducing agent Fe(II) Before Start of titration Redox titration Oxidising agent Ce (IV) Redox Indicator During process of titration At end point Fe (II) Indicator(reduced form) ,Fe(III),Ce(III) Oxidising agent Ce (IV) Indicator (Oxidised form),Fe(III),Ce(III) Titrimetric methods 10