Application of conductance measurement

simple concept about the applications of conductance measurement

1. P resented by : Sara Anwar Topic : “APPLICATION OF CONDUCTANCE MEASUREMENT ”

2. 1: Determination of degree of dissociation of weak electrolyte 2: Determination of ionization constant of acids 3: Determination of solubilty product ( k sp ) of sparingly soluble salt 4: Calculation of ionic product of water 5: C onductometric titration

3. Determination of degree of dissociation: “Degree of dissociation is the fraction of the total number of molecules dissociated into ions .” Degree of dissociation ( ᾳ ) = No. of molecules dissociated into ions Total no. of molecules present No. of molecules dissociated is directly proportional to conductivity of the molecules. No. of molecules dissociated in to ions λ m c ( molar conductivity at a particular concentration.) Total no. of molecules λ m ∞ (molar conductivity at infinite concentration) ᾳ (degree of dissociation) = λ m c / λ m ∞ 1:

4. 2:Determination of ionization constant of acids: The  acid ionization constant , also called the 'acid dissociation constant' or 'acidity constant,' is a measure of how much of the acid is  deprotonated  (which is when it's unbound to a hydrogen), compared to molecules still bound to a hydrogen . example :acetic acid (left) (right) CH 3 COOH CH 3 COO _ + H + at time C t C-C ᾳ C ᾳ C ᾳ [ C ᾳ is dissociated part ]

5. According to the law of mass action : “The rate of chemical reaction is directly proportional to the product of active masses of reactiong substances.” K a = C ᾳ C ᾳ C(1- ᾳ ) K a = C ᾳ C ᾳ C(1- ᾳ ) K a = C ᾳ 2 1- ᾳ [ ᾳ is of dissociation ]

6. 3)Determination of solubility product ( k sp ) of sparingly soluble salt : Solubility product: When a sparingly soluble salt is placed in water, a very small amount of the salt dissolves in the water and a solution is formed. The solubility product, K sp , determines the equilibrium that exists between the sparingly soluble salt and the ions that are dissolved in water Example : AgCl (s) Ag + ( aq ) + Cl - ( aq )

7. K sp = [ Ag + ][ Cl - ] if the s is the solubilty of AgCl then : [ Ag + ] = s & [ Cl - ]= s K sp =( s ) ( s ) K sp = s 2

8. 4)Calculation of ionic product of water: Water has electrical conductivity, hence it must undergo dissociation . Dissociation of pure water to a very little extent into H+ and OH – ions by itself is called as self ionization of water . Water is very weak electrolyte . In water an equilibrium between ions an unionized water molecules exists as : H 2 O H + + OH - H + + H 2 O H 3 O + the net reaction is H 2 O + H 2 O H3O+ +OH-

9. Applying the law of mass action to above equilibirium , we have k W =[H3O+][OH- ]/ [H 2 O] 2 (1) Now water is very weak electrolyte . It dissociate in a very small amount . H ence practically the concentration of unionized water is almost the same as starting concentration .hence H2O =1=constant . similarly that H + ( aq )  actually refers to a hydroxonium ion. Therefore the 1 st equation becomes: k W [constant]=[H+][OH-] (2) K W =[H + ][OH - ] the relation is known as the ionic product of water

10. When small amount of acid is added to water , the concentration of [H + ] increases and the concentration of [OH - ] decreases When small amount of alkali is added to water , [OH - ] ions concentration becomes higher than that of [H + ] ion concentration In neutral solution, [H + ] and [OH - ] ion concentration are equal Thus the concept of ionic products of water helps us in classifying the aqueous solution as an acid , base or neutral.

11. 5 ) CONDUCTOMETRIC TITRATION “The determination of end point of a titration by the means of conductivity measurements are known as conductometric titration” TYPES OF CONDUCTOMETRIC TITRATIONS acid-base titration Precipitation titration Replacement titration Redox ( oxidation-reduction) titration Complexometric titration

12. - --- Burette (strong acid e.g HCL) Electrodes Battery + __ Beaker (strong base e.g NAOH) CONDUCTOMETER Acid – base titration : HCL NAOH H 2 O+NACL

13. HCL NAOH 1 2 3

14. FACTORS AFFECTING CONDUCTIVITY: Size of ions Temperature Charge of ions Numbers of ions

15. Principals: Conductometry is the ability to measure the ability of electrolyte carry current . Conductrometry is depends on the ions present in the electrolyte . As the number of ions in the solution decreases the conductivity decreases and vise versa . The point from which the conductance remains constant is neutralization point which indicates the end point of reaction .

16. Advantages of the conduct metric titration : No need of indicator Colored or dilute solution can be used for titration . End point can be determined accurately.

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