CONDUCTOMETRY PART-2: Instrumentation and Conductometry Titration with Question-Answer

CONDUCTOMETRY PART-2: Instrumentation and Conductometry Titration with Question-Answer

INSTRUMENTATION OF CONDUCTOMETER :-

Conductometry

Conductometry

Pipette drawing titration, Picture #2723698 pipette drawing titration

  1. Current source :- Alternative current source is used. High frequency alternating current generator is employed. electrical potential is applied ions will be transfer and ultimately conductance take place.
  2. Conductivity meter :- Digital display, calibrator,power switch.
  3. Conductivity cell :- Made of pyrex or quartz and are fitted with two platinum electrodes. Should be placed in vessel containing water to maintain constant temp. types of conductivity cells are TYPE-A, TYPE-B, & TYPE-C.
  4. Electrodes :- Platinum sheets each of 1 cm are fixed at distance of 1 cm. the surface is coated with platinum black to avoid polarization effect & increase effective surface area. platinisation of electrodes is done by coating solutions 3% chlorplatinic acid & lead acetate on it to gel uniform coating. electrode usage depends on conductivity & concentration.

CONDUCTOMETRIC TITRATION :-

  • Determination of end point of a titration with the help of conductivity measurements is termed as conductometric titrations.
  • In a conductometric titration the titrant is added.
  • The values of conductivity are then plotted against the volume of the titrant in C.C.
  • Since the measured conductivity is a linear function of the conc. of ions present two lines will be obtained which will intersect each other at a point known as “end point” or ”equivalence point”

TYPES OF CONDUCTOMETRIC TITRATION :-

  1. Acid base titration
  2. Replacement titration
  3. Redox titration
  4. Complexometric titration
  5. Precipitation titration

  ACID – BASE TITRATION :-

Strong acid- strong base titration  :- Fall in conductance due to replacement of high conductivity hydrogen ions by poor conductivity of sodium ions. Rise in conductance due to increase in hydroxyl ions.

e.g. HCl vs NaOH

• Strong acid – weak base titration :- Fall in conductance due to replacement of hydrogen by ammonium ions. conductance remain constant due to suppression of NH4OH by NH4Cl

e.g. HCl vs NH4OH

• Weak acid – strong base  titration:- Initial decrease in conductance followed by increase due to NaOH.

e.g. CH3OOH VS NaOH

• Weak acid – weak base  titration :- Increase in conductance due to excess of CH3COOH. Constant conductance due to suppression of NH4OH by CH3COOH.

e.g. CH3OOH VS NH4OH

Conductometric Titration of Strong Acid and Strong Base - QS Study

Which indicator is used in a strong acid versus a strong base ...

 

MCQ.

1. Conductivity cells are made up of

a. Two silver rods

b. Two parallel sheets of platinCm

c. Glass membrane of Ag/AgCl

d.Sb-Sb2o3

2. The units for specifi conductance is :

a.Ohms

b.Ohms cm

c.Mhos

d.Mhos cm

3. Which is not type of conductivity cells?

a.TYPE-A

b.TYPE-B

c.TYPE-C

d.TYPE-D

4. Which material are used for coating a conductivity cell ?

a. Platinum black

b. Platinum

c. Copper

d. Iron

5. Which material are use in old platinisation of conductivity electrode ?

a. Chloroplatinic acid

b. Acetic acid

c. Sulphuric acid

d. Nitric acid

ANSWER KEY :-

1.b

2.b

3.d

4.a

5.a

REFERENCE 

TEXT BOOK OF PHARMACEUTICAL ANALYSIS THIRD EDITION Dr.S. RAVI SANKAR (PAGE NO. 10.1-10.15)

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