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II. Conductometry

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I = V / R II. Conductometry Dr. Hisham Ezzat Abdellatef Introduction Conductance: is the ability of the medium to carry the electric current. migration of ... – PowerPoint PPT presentation

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Title: II. Conductometry


1
II. Conductometry
I V / R     
  • Dr. Hisham Ezzat Abdellatef

2
Introduction
  • Conductance is the ability of the medium to
    carry the electric current.
  • migration of positively charged species towards
    the cathode and negatively charged ones through
    the anode

ohm-1(seimen)
E is the potential difference, i is the
current intensity.
From Ohm low
3
The conductance of the solution depends on
  • 1. Temperature
  • It is increased by increase of temperature.
  • 2. Nature of ions
  • size, molecular weight, number of charges the ion
    carries and other factors
  • 3. The concentration of ions
  • As the number of ions increases the conductance
    of the solution increases.
  • 4. The size of the electrodes

L/A is cell constant K is the specific
conductance or conductivity ohm-1cm-1 or
seimen/cm.
4
  • Equivalent conductance ?
  • It is defined as the conductance of one gram
    equivalent of solute contained between electrodes
    spaced one centimeter apart.
  • Where C is the concentration in gram equivalent
    per liter.
  • Equivalent ionic conductance
  • At infinite dilution, interactions become nil
  • the overall conductance of the solution consists
  • of the sum of the individual equivalent ionic
  • conductance
  • ?o ?o ?-o

5
Instrumentments
  • Two parts
  • conductivity bridge.
  • Conductance cell

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Application of conductivity 
  1. Direct or absolute measurments
  • checking purity of distilled water or other
    chemicals.
  • determination of physical constants such as
  • ionization constant.

2. Conductometric titrations
  • Very dilute solutions.
  • Turbid and highly coloured solutions.
  • Reaction which is not complete and where there is
    no suitable indicator,
  • e.g. reaction between weak acid
    and weak base.

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  • 1. Titration of strong acid with strong base
  •  The reaction is represented by the following
    equations
  • e.g. H Cl- Na OH- ? H2O Na
    Cl-

17
  • 2. Very weak acid with strong base or a very weak
    base with stronger acids

18
  • Determination of mixture of hydrochloric acid
    (strong acid) and acetic acid (weak acid) with
    sodium hydroxide (strong base)

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  • 3. Precipitation and complex formation reaction
  • Na Cl- Ag NO3- ? AgCl Na
    NO3-

20
  • Conductivity as a function of the volume of added
    standard solution in the titration of an
    approximately 0.1 molar acetic acid solution (V
    5 ml) with a sodium hydroxide solution (c 0.1
    mol l-1)

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