Transport électrique

Conductance (G) measures how easily electricity flows through a solution and depends on cell geometry. Specific conductance (κ) removes geometric effects by multiplying conductance by the cell constant, which is the electrode distance divided by cross-sectional area. Specific conductance represents the conductance of a one-meter cube of solution, measured in Siemens per meter (S/m).

As electrolyte dilution increases, molar conductance (Λm) increases due to greater electrolyte dissociation and increased ion mobility. However, specific conductance (κ) decreases because the total number of ions per unit volume drops despite higher dissociation. At infinite dilution, strong electrolytes reach a limiting molar conductance value (Λ°m).

The cell constant (Kcell) is defined as the distance between electrodes divided by their cross-sectional area. It removes the effect of cell geometry from conductance measurements, allowing conductance values to be compared across different measurement setups. Multiplying conductance by the cell constant yields specific conductance, which is independent of apparatus design.

Equivalent conductance (Λ) represents the conductance of ions from one gram equivalent of electrolyte, while molar conductance (Λm) represents conductance from one mole of electrolyte. Both are calculated from specific conductance (κ), but molar conductance is more useful because it reveals how ion mobility and electrolyte dissociation vary with concentration in theory of strong electrolytes.

During dilution, electrolyte dissociation increases, raising molar conductance. However, the rise in ion numbers is significantly less than the increase in solution volume. Consequently, the total ion concentration per unit volume decreases, causing specific conductance to decline despite improved ion mobility and higher molar conductance values.

Molar conductance at infinite dilution (Λ°m) is the limiting value that strong electrolytes approach as concentration approaches zero. This value is used in conductometric titrations strong acid base and weak acid base titrations to determine the degree of dissociation and ion mobility under ideal conditions where electrostatic interactions between ions are minimized.

Molar conductance (Λm) is calculated by dividing specific conductance (κ) by the molar concentration of the electrolyte in the solution. This relationship allows researchers to determine how conductivity changes with electrolyte concentration, revealing information about ion mobility and dissociation behavior across different concentration ranges.