Electrolytic Conduction

Introduction

When dissolved in a polarised liquid such as water, or sometimes when melted, electrolytes have the property of being charge-conducting mediators. A good example of an electrolyte is NaCl or table salt.

Once the electrolytes dissolve, they form so-called electrolyte conductors. When exposed to an electric field, sodium and chloride ions flow in opposite directions, creating a charge flow. That is, they form an electric current.

As a conducting medium, electrolytic conductors behave differently than conventional conductors. The electric current in conductors occurs only as a flow of electrons because there is a “sea of free electrons” in them, independent of the nucleus where the accompanying protons reside.

Electrolytic conductivity

When a voltage is applied to an electrode immersed in an electrolyte solution, ions move from the electrolyte, so current flows through the electrolyte solution. The ability of an electrolyte to conduct electric current is called conductance or conductivity.

(1) Ohm’s Law: This law states that the current flowing through a conductor is proportional to the potential difference across it, i.e. I is proportional to V

where I is the current intensity (in amps) and V is the potential difference (in volts) applied across the conductor

or I=V/R or V=IR

where R is denoted as a proportionality constant called the resistance of the conductor. It is expressed in Ohms and expressed as the above equation called Ohm’s Law. 

The current flowing through a conductor is proportional to the potential difference applied across the conductor and inversely proportional to the resistance of the conductor.

(2) Resistance: measure the resistance to current flow. The specific conductor resistance is proportional to the length (l) and inversely proportional to the cross-sectional area (a), so

Here ⍴( rho ) is the proportionality constant called specific resistance or resistivity. Resistance depends on the properties of the material.

Unit: The unit of resistance is ohms Ω expressed in SI unit, the basic unit is equal to (Kgm2)/(s3A2)

(3) Resistance or specific resistance: we know that the resistance R is R=⍴(l/a); now if l = 1 cm, a = 1 cm2 then R=⍴

Therefore, resistivity is defined as the resistance of a conductor with a length of 1 cm and a cross-section equal to 1 cm2

Unit: The resistance unit is ⍴=R.(a/l)=Ω(cm2/cm)

The SI unit is metre ohms(Ω-m) but centimetre ohms (cm-Ω) are also often used.

(4) Conductance: A measure of the ease with which current flows through a conductor. This is an additional property. It can be represented by G. It is the inverse of resistance,

G=1/R

Units: Conductivity units are reciprocal ohms (Ω-1) or mho. Ohm is also abbreviated as so that Ohm-1 can be written as Ω-1

According to the SI system, the unit of conductivity is Siemens, S (i.e. 1s=1Ω-1)

(5) Conductivity: The reciprocal of resistivity is called conductivity (or specific conductivity). It is represented by the symbol k (Greek kappa). IUPAC recommends using the term conductivity rather than specific conductivity. It can be defined as the conductivity of a solution with a length of 1 cm and a diameter of 1 cm. 

k=1/⍴

Unit: The conductivity unit is k=1/(Ω-cm)=Ω-1cm-1

In SI units, l is expressed as m cross-section in m2, so the conductivity Sm-1

(6) Molar conductivity or molar conductivity: Molar conductivity can be defined as the conductivity of all the ions produced by dissolving one mole of electrolyte in solution.

It is denoted by (λ). Molar conduction is related to specific conduction (k) because,

Λ=k/M

where M is the molar concentration.

If M is expressed in molarity units, ie moles per litre (mol L-1), then λ can be expressed 

For placing a solution containing 1 g mol of electrolyte between two parallel electrodes 1 cm² in diameter and 1 cm apart,

Conductance(G)=Conductivity=Molar Conductivity(Λ)

But if the solution contains 1 g mol of electrolyte, then the measured conductivity is the molar conductivity.

Molar Conductivity(Λ)=100*conductivity

Molar Conductivity Unit: The molar conductivity unit can be derived from the formula,

Λ=(k*1000)/M

The unit of Κ is S-cm-1 and the unit of λ is,

Λ= S-cm-1*(cm3/mol)=S-cm2mol-1

According to the SI system, if the concentration is expressed in mol-m3 the molar conductivity is expressed in S-m2,mol-1.

(7) Equivalent conductivity: It can be defined as the conductivity of all ions generated by dissolving one gram equivalent of electrolyte in solution.

It is expressed as and is related to the specific conductivity as

Λe=(k*1000)/C=k*(1000/M)………….[M is the molarity of the solution]

where C is the concentration in gram equivalents per litre (or equivalent). This word is often used. It is now replaced by molar conduction. Equivalent conductance are Ω-1cm2 (gm Equiv)-1

Conclusion

Electrolytes are substances that dissolve in a solvent and break down into charged ions; positive ions are called cations, and negative ions are called anions. So, in the case of metals, conduction is due to the flow of electron charge. In the electrolyte, the charged particles present are ions, so the electrolyte is able to conduct an electric current. Some materials like insulators impede the free flow of electrons from one particle of an element to another. A conductor is a material that allows electrons to flow freely from one particle to another. These are elements with electrical charges in the form of electrons that can move relatively freely in the material. Therefore the ability of electrolyte solutions to allow current to flow through them is called electrolyte conduction.