Electrical Conductance

Electrolyte

A chemical compound that ionizes when dissolved in water or molten that can conduct electricity.

"Substances like acid, base and salts which can conduct electricity in their aqueous solution due to ionization are known as electrolytes."

The presence of ions in solution is responsible for the conduction and when the current passes through the wires, it shows the movement of free electrons through wire

Electrolysis Cell

Arrhenius’ Theory of Electrical Conductivity

The first modern theory to explain electrical conductivity in solutions was advanced by Svante Arrhenius, at the time a doctoral student in physics at the University of Uppsala, Sweden.

He deduced that, the presence of charged particles in an electrically conductive solution, and he postulated that the extent of the conductivity depended on the number of ions present.

Hence the solute in a strong electrolyte would produce many ions and conduct electricity well, while the solute in a weak electrolyte would produce relatively few ions and not conduct electricity very well.

In a non electrolyte, the solute would produce no ions, hence no electrical conductivity for these solutions.

Types of Electrolytes 1. Strong Electrolytes:

Solutions whose electrical conductivity is high. They are good conductors of electricity.

2. Weak Electrolytes:

Solutions that conduct electricity, but not very well. They are still called conductors, but only poor conductors.

3. Non Electrolytes:

Non electrolytes do not conduct electricity.

Strong electrolyte

Weak electrolyte Non electrolyte

Strong Electrolyte Electrical conductivity of

aqueous solutions. The circuit will be completed and will allow current to flow only when there are charge carriers (ions) in the solution.

Example :

Hydrochloric acid solution, which is a strong electrolyte, contains ions that readily conduct the current and give a brightly bulb.

• Strong electrolytes are 100% dissociated (completely ionized )in their aqueous solution.

• Strong electrolytes like salts are composed of

oppositely charged ions. • In solid state, these ions are held by strong

electrostatic forces of attractions. Classes of strong electrolytes : (i) Soluble salts (ii) Strong acids (iii) Strong bases

(I) Soluble salt

When solid NaCl dissolves, the Na+ and Cl- ions are randomly dispersed in water.

Any salt that readily dissolves in water produces a strong electrolyte when it is dissolved.

According to Arrhenius, an acid is a substance that ionizes in aqueous solution to generate H+ ions .

If the ionization is complete or nearly complete, the acid solution is a good conductor of electricity, and the acid is regarded as a strong acid.

(II) Strong acids

Example :

HCl completely ionized in water

According to Arrhenius, a base is a substance that ionizes in aqueous solution to produce hydroxide ions (OH-).

Bases that ionize completely are regarded as strong bases. The two most common strong bases are sodium hydroxide (NaOH) and potassium hydroxide (KOH).

(III) Strong bases

Example :

NaOH completely ionized in water

List of Strong Electrolytes Potassium

chloride

Sodium hydroxide

Sodium nitrate

Sulfuric acid

Nitric acid

Potassium hydroxide

Weak Electrolyte Electrolytes which are weakly ionized in their aqueous solution are called as weak electrolytes.

Example :

Acetic acid solution, which is a weak electrolyte, contains only few ions and does not conduct as much current as a strong electrolyte.

The bulb is only dimly lit

Some substances will form ions in aqueous solution, but the extent of ionization is slight.

In the aqueous solution of weak electrolytes, the constituent ions are in equilibrium with un-dissociated molecules of electrolytes.

The result is a solution that is electrically conductive, but much less so than a comparative solution containing a strong electrolyte.

The most common weak electrolytes are:

Weak acids

Weak bases

Weak acids A weak acid is an acid that is

only partially ionized in aqueous solution.

An aqueous solution of acetic acid (HC2H3O2) contains some hydrogen ions (H+(aq)) and some acetate ions (C2H3O2

-(aq)), but most of the solute particles are undissociated acetic acid molecules (HC2H3O2(aq)).

Example :

The reaction of HC2H3O2 in water

Ammonia (NH3) is the most common of the weak bases.

It is a base because its aqueous solutions contains (OH-) ions

It is a weak electrolyte because only a small fraction of ammonia molecules form ions. Most of the ammonia remains as neutral ammonia molecules.

Example :

The reaction of NH3 in water

Weak bases

NH3 (aq) + H2O (l) ——> <——

NH4+(aq) + OH-(aq)

List of Weak Electrolytes

Hydrocyanic acid

Acetic acid

Ammonia

Ammonium hydroxide

Hydrofluoric acid

Oxalic acid

Pyridine

Non Electrolyte

Substances which cannot conduct electricity in their aqueous solution due to the absence of ions.

They are generally polar or non-polar covalent compounds which can dissolve in water as molecules instead of ions.

Example :

A sucrose solution, which is a non electrolyte, contains no ions and does not conduct current

The bulb remains unlit.

List of Non Electrolytes

Sucrose Glucose Ethanol Methanol Carbon

tetrachloride Kerosene Gylcerol Oxygen

Debye–Hückel Theory

The Debye–Hü ckel Theory were derived by Peter Debye (Dutch physical chemist) and Erich Hückel (German physicist), who developed a theory with which to calculate activity coefficients of electrolyte solutions.

The activity is proportional to the concentration by a factor known as the activity coefficient , and takes into account the interaction energy of ions in the solution

1. The decreased in the molar conductivity of a strong electrolyte was attributed to the mutual interference of the ions, which becomes more pronounced as the concentration increased.

2. Distribution of ions in solution. The distribution of the negative ions and positive ions is not symmetric.

If an electric potential is applied, the positive ions will move towards the negative electrode and drag along the negative ions.

The more concentrated the solution, the closer these negative ions under consideration, and the greater is the drag.

The ionic atmosphere around the moving ion is therefore not symmetry, the charged density behind is greater than that in front and will result in a retardation