NEET Chemistry Notes Electrochemistry – Concept of Electrochemistry

NEET Chemistry Notes Electrochemistry – Concept of Electrochemistry

Concept of Electrochemistry

Concept of Electrochemistry

The study of the chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor is considered under the branch of chemistry namely as electrochemistry.

Conductors

The substance which can conduct electricity are called conductors. On the basis of species that conduct electricity (current)

conductors are of two types:

• Metallic or electronic conductors conduct current by transfer of free electrons.
• Electrolytic conductors conduct current by the mobility of ions.

Conductance in Electrolytic Solutions

The power of an electrolyte to conduct electric current is called conductance or conductivity. Just like metallic conductors, electrolytic solutions also obey Ohm’s law.

Conductance (C)
Reciprocal of resistance is called conductance, C

Conductivity or Specific Conductance (K)
The resistance of any conductor varies directly as its length (l) and inversely as
its cross sectional area (a)
where, ρ is called the resistivity or specific resistance.

where,  = cell constant, it is determined with the a
help of conductivity bridge, where a standard solution of KCl is used.
The unit of specific conductance (K) is ohm^-1 cm^-1 or S cm^-1.

 Molar Conductivity

It is the conducting power of all the ions produced by one gram mole of an electrolyte in a given solution.

The units for molar conductivity = ohm^-1 cm²mol^-1 orScm² mol^-1

Equivalent Conductivity

It is the conducting power of all the ions produced by one gram equivalent of an electrolyte in a given solution.
Thus
The units for equivalent q normality
conductivity = ohm^-1 cm² (geq)^-1 or S cm² (g eq)^-1

 Effect of Dilution on Conductivity

Equivalent as well as molar conductivity  dilution
and specific conductivity

Variation of Molar and Equivalent Conductivities with Concentration

In case of strong electrolytes, like KCl have high value of conductance even at low concentration and there is no rapid increase in their equivalent or molar conductance on dilution.

In case of weak electrolytes, like acetic acid, have a low value of conductance at high concentration and there is a rapid increase in the value of equivalent conductance [molar conductance) with dilution.

Limiting Molar Conductivity or Infinite Conductivity
It is the molar conductivity of electrolyte when concentration of electrolyte approaches zero (i.e. at infinite dilution).

Kohlrausch’s Law

It states that molar conductance at infinite dilution for any electrolyte is the sum of contribution of its constituent ions, i.e. anions and cations.

Applications of Kohlrausch’s Law

•  For the determination of equivalent/molar conductivity at infinite dilution.
• For the determination of degree of dissociation
  
• For the calculation of dissociation constant of a weak electrolyte.
  
  Here, K_a = equilibrium dissociation constant
  C = molar concentration of weak electrolyte
•  For the determination of solubility of sparingly soluble salt.
  
• Absolute ionic mobilities is defined as the speed of ions in cm per second at infinite dilution under a potential gradient of 1 V/cm. Its units are cm s’¹ N cm’¹.

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