Ion mobility in a solution is essential for conducting electricity. The ability of an electrolytic solution to permit electric current to flow through it is known as its conductance. This characteristic is essential to electrochemistry and has many uses in both daily life and industry.
What Conductance of Electrolytic Solutions?
Dissolving in water, an electrolyte (like salt, acid, or base) separates into positively charged (cations) and negatively charged (anions) ions. When an external voltage is applied, these ions carry electric current and are free to move around in the solution. This movement of ions enables the electrolytic solution to conduct electricity, and called conductance.
For example, when sodium chloride (NaCl) dissolves in water, it dissociates into: NaCl → Na+ + Cl−
Here, the electric current is carried by the sodium ion (Na⁺) and the chloride ion (Cl⁻). The solution’s ability to conduct electricity improves with the quantity of free ions present.
Factors Affecting Conductance
Following factors influence the conductance of an electrolytic solution:
Nature of the Electrolyte:
Strong electrolytes (e.g., HCl, NaOH, NaCl) dissociate completely in water, leading to high conductance.
Weak electrolytes (e.g., CH₃COOH, NH₄OH) partially ionize, resulting in lower conductance.
Concentration of the Electrolyte:
Conductance rises in diluted solutions due to the increased mobility of ions.
Ion pairing lowers conductivity in highly concentrated liquids.
Temperature:
Raised temperatures improve conductance by increasing ion mobility.
Reduced conductance results from less ion movement at lower temperatures.
Viscosity of the Solvent:
Conductance is decreased when ion transport is slowed down by a particularly thick or viscous solvent, such as water.
Conductance increases when ions can flow freely in a less viscous fluid.
Size of the Ions:
Smaller ions conduct electricity better and move more quickly.
Larger ions contribute less to conductance because they move slowly.
Applied Voltage and Electrodes:
Increased voltage improves conductance by increasing ion mobility.
Ion interaction and conductance are also influenced by the electrode material (such as platinum).
Types of Conductance
Specific Conductance (κ or kappa):
It is the conductance of an electrolyte solution per unit volume (1 cm³).
Siemens per meter (S/m) or Siemens per centimeter (S/cm) are the units of measurement.
Molar Conductance (Λm):
The conductance of every ion in a single mole of electrolyte dissolved in a specific volume of solution.
Formula: Λm = k / C where k = specific conductance and C = concentration in moles per liter.
Equivalent Conductance (Λeq):
It is defined as the conductance of one electrolyte equivalent (gram equivalent) dissolved in solution.
The following relation it to molar conductance:
Λeq = Λm / n where n is the number of equivalents per mole.
Types of substances on the Basis of Conductivity:
Materials are classified into following types:-
Insulators: Substances which have very low conductivity in the range of 10-20 to 10-10 S m-1 are called insulators e.g; plastics, wood, coal etc.
Semiconductors: Substances which have moderate conductivity in the range of 10-6 to 104 S m-1 are called semiconductors. These are intrinsic (An intrinsic semiconductor, also called a pure semiconductor, undoped semiconductor or i-type semiconductor, is a semiconductor without any significant dopant) and extrinsic (An extrinsic semiconductor is a semiconductor that has been doped with a small amount of a chemical impurity. This process is called doping.) semiconductors.
Conductors: Substances which have very large conductivity in range of 104 to 107 S m-1 are known as conductors e.g; metals and their alloys, certain non-metals like carbon black, graphite and some organic polymers.
Superconductors: Materials which have zero resistivity and infinite conductivity are called superconductors e.g; metals and their alloys at very low temperature 0 15 K. Ceramic materials and mixed oxides behave as superconductors upto 150 K.
Kohlrausch’s Law
Kohlrausch’s Law of Independent Migration of Ions states that:
“The limiting molar conductivity of an electrolyte is the sum of the individual contributions of its cations and anions.”
Mathematically, Λm0 = λ+ + λ−
where λ⁺ and λ⁻ are the contributions of the cation and anion to molar conductance.
For example, for NaCl:
Λm0 (NaCl) = λ0 (Na+) + λ0 (Cl−)
This law helps in finding out weak electrolytes’ conductance, which is impossible to test directly.
Applications of Electrolytic Conductance
Purity Testing of Water:
Conductance aids in identifying contaminants (such as dissolved salts) in water.
The conductivity of pure water is very low.
Electroplating & Battery Performance:
Conductance guarantees effective metal deposition in electroplating.
Electrolyte conductance determines battery efficiency.
Medical Applications:
Used to determine the concentration of ions in bodily fluids, such as blood and urine.
Industrial Applications:
Used to track reactions in the production of chemicals.
Assists in food and pharmaceutical quality control.
Summary
One essential characteristic of an electrolytic solution is its conductance, which is influenced by the electrolyte’s composition, temperature, concentration, and ion mobility. Because they completely dissociate, strong electrolytes conduct well, whereas weak electrolytes conduct less. Electrolyte behaviour can be studied using a variety of conductance measurements, including specific, molar, and equivalent conductance. Applications are medical diagnostics, battery performance, and water purity testing.
Scientists and engineers can create safer drinking water, enhance industrial processes, and create better batteries by researching electrolytic conductivity. It makes up a tiny but important portion of the field of electrochemistry.
The ability of an electrolytic solution to permit electric current to flow through it is known as conductance. When a voltage is supplied, it is dependent upon how the ions in the solution travel.
The ability of an electrolytic solution to permit electric current to flow through it is known as conductance. When a voltage is supplied, it is dependent upon how the ions in the solution travel.
Following factors are influence the conductance:
Nature of the electrolyte (strong or weak)
Concentration of the solution
Temperature (higher temperature increases conductance)
Viscosity of the solvent
Size and mobility of ions
Applied voltage and electrode material
Specific Conductance (κ): Conductance of a unit volume (1 cm³) of solution, measured in Siemens per meter (S/m) or Siemens per centimeter or (S/cm).
Molar Conductance (Λm): Conductance of 1 mole of electrolyte in a given volume, calculated as: Λm = k / C where k is specific conductance and C is molarity.
Ions can flow more quickly at higher temperatures because of their increased kinetic energy, which improves conductance. In general, conductivity increases as temperature rises.
Kohlrausch’s law states that the molar conductance of an electrolyte at infinite dilution is the sum of the individual conductances of its cation and anion: Λm0 = λ+ + λ−
It helps in determining the conductance of weak electrolytes by adding the contributions of their respective ions.
Strong electrolytes have high conductance (such as NaCl and HCl) fully dissociating into ions in solution, which permits a large number of charge carriers. Weak electrolytes, such as CH3COOH and NH3OH, partially ionize, which reduces conductance.
Conductance plays a role in:
Water purity testing (low conductance means pure water)
Batteries and fuel cells
Electroplating and metal refining
Medical diagnostics (measuring ion concentration in blood & urine)
Chemical and pharmaceutical industries for quality control