II. Conductometry

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II. Conductometry
I V / R     

• Dr. Hisham Ezzat Abdellatef

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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
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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.
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• 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

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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-

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

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• 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-

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• 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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