Here the electrical conducting capacity (which is because of ions) of the solution is measured and it is the basis for analysis. The ions will move from cathode to anode based on the change in either direction. Mobility is the measure of rate at which the ion on moving in solution on application of electrical or because of the difference in concentration.
CONDUCTOMETRIC TITRATIONS Here the conductivity is taken on Y-axis and titrant on X-axis. There comes the two lines (as conductivity gives linear lines) and by extrapolating this the end pont can be determined.
Actual conductivity is given by the formula
= (v+V/V)*observed conductivity
v- Volume of the titrant
I) Acid-base titrations: Hydrogen and hydroxyl ions move more easily than other agents and this is the basis of acid base titrations.
a) Strong acid Vs Strong Base:
E.g., [H+ + Cl-] +[Na+ + OH-] ----> [Na+ + Cl-] + H2O
In the beginning, the acid concentration will be high and so H+ conductance is more. But as NaOH is added, Na+ ions replace H+ ions. So the conductance decreases and at neutralization there will be least conductivity. And as the NaOH concentration os increased, again the conductivity increases because of OH- ions.
b) Strong acid Vs Weak Base:
E.g., [H+ + Cl-] + [NH4+ + OH-] ---> [NH4+ + Cl-] + H2
In this case, initially the conductance will be more because of H+ ions. But if once the NH4+ OH- is added, H+ ions will be replaced by NH4+ ions and so the conductivity decreases. As NH4OH is a weak base, it do not dissociate and so after neutralization the conductivity do not increase.
c) Weak acid vs Strong Base:
e.g., [CH3COO-+ H+] + [Na+ + OH-] ---> [CH3COO- + Na+] + H2O
Take CH3COOH and is titrated with NaOH. Once we add NaOH, it still decreases and then the conductivity will increase. And after neutralization, because of OH- ions, the conductivity again increases.
d) Weak Acid vs Weak Base: Initially, the conductance decrease and then raises until the end point is achieved. The increase in conductance before the end point is due to formation of CH3COONa. If excess of base is added then conductivity increases.
II) Replacement titrations: Initially the salt of weak acid and strong base is taken and strong acid is gradually added. This results in the replacement of weak acid. Initially the conductance will be raise very slowly and after the end point, suddenly the conductivity will increase.
III) Precipitation titrations: In this type of titrations, the ion which is to be replaced with another ion having less rate of flow. This gives wide variation in conductivity . In this reaction between mgso4 and Ba(OH)2(both of them are not completely soluble) initially conductance decreases but once the end point is reached, the conductivity increases.
IV) Redox titrations:In these titrations, there will be reduction in the number of hydrogen ions. So the conductivity will reduce as the number H+ ions are decreased.
These are also useful for studying the complex compounds.
I) This is used for the determination of alkalinity present in weak organic acids. Ostwald proposed a formula for this.
II) If a sparingly soluble salt is added to water, some amount will get solubilized and the remaining will go and form a layer at bottom. Now we can consider that saturation has been achieved and salt is in completely ionized form. Then
III) Ionic product(Kw) can be calculated by the formula
IV) The degree of dissociation in the case of weak electrolysis is given by
V) It is also used to estimate the amount of vanillin present in the vanillin essence. Dissolve 5g of salt in 40ml of water. Add this solution to 10ml of essence. Now pour this solution into separating funnel. Now HCl(6N) and 40-60ml of ether are added. Now the aqueous and ether will separate. Now remove water and wash the ether with distilled water. Now evaporate ether and dissolve it in10ml of alchol. Now add 75ml of water. Conduct conductometric titration and compare it with pure vanillin.
Reference: Instrumental Methods of Chemical Analysis by Gurdeep R. Chatwal and Sham K. Anand,Himalaya Publishing house,Reprint 2011,page no2.482 to 2.496
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