The interionic forces of the strong electrolytes depend on the solvent's dielectric constant, which is the ability of a solvent to store electrical energy, based on its polarizability. and the solution's concentration. In high-dielectric solvents and in dilute solutions, weak electrostatic forces keep ions apart. However, in low-dielectric solvents or concentrated solutions, stronger interionic forces may cause ions to pair up as ionic doublets despite being fully ionized. The theory of strong electrolytes also suggests that strong electrolytes maintain a degree of ionization of unity even at substantial concentrations. Debye and Hückel introduced the concept that the increase in molar conductance with dilution for strong electrolytes is a result of heightened ion mobilities because of reduced interionic attractions, not increased ionization. This theory posits that in strong electrolytes, the interionic attraction, rather than partial dissociation, accounts for the decrease in conductivity with increasing concentration. Debye and Huckel's equation measures the impact of interionic effects, proposing that each ion is surrounded by an 'ionic atmosphere' of opposite charge. This atmosphere is shaped by the coulombic interactions and thermal collisions between ions and solvent molecules. At high temperatures, this structure becomes less organized due to increased thermal collisions. When an electric field is applied, the ions move, disrupting the ionic atmosphere's symmetry and slowing down the ion movement, known as the 'asymmetry effect.' At higher concentrations, ion movement can be slowed down due to the electrophoretic and viscous effects. The electrophoretic effect occurs when the ionic atmosphere associated with water molecules moves in the opposite direction to the central ion, creating counter-currents that impede ion movement. The viscous effect results from the solvent's viscous drag on the ions' movement. The more viscous the solvent, the stronger the drag, resulting in decreased ionic mobility and conductance.
The theory of strong electrolytes describes strong electrolytes as substances that ionize completely in solution at all concentrations up to their saturation point. The interionic forces still act, depending on the solvent's dielectric constant and solution concentration.
For instance, in high-dielectric solvents like water, electrostatic forces between ions are relatively weak.
Despite complete ionization, molar conductance decreases with increasing concentration due to stronger interionic attractions that hinder ionic mobilities.
This theory also says that each ion is surrounded by an 'ionic atmosphere' of oppositely charged ions.
The application of an electric field moves the ions, disrupting the atmosphere's symmetry and slowing down the central ion’s movement—a phenomenon called the asymmetry effect.
Simultaneously, the electrophoretic effect, where the ionic atmosphere and the related solvent molecules move in the opposite direction of the central ion, creates a counter-current that further slows ion movement.
The viscous effect adds frictional drag from the solvent, further reducing ionic mobility and conductance.
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