Conductivity & Concentration Calculator

Conductivity ↔ Concentration Calculator

Conductivity and Concentration

Electrical Conductivity (κ, kappa) measures a material's ability to conduct electric current. In solutions, conductivity is primarily due to the movement of dissolved ions. It depends on the number of ions, their charge, and their mobility.

Molar Conductivity (Λm, Lambda_m) relates the conductivity to the molar concentration (c) of the electrolyte: Λm = κ / c. It essentially represents the conductivity per mole of electrolyte. Molar conductivity generally decreases as concentration increases due to inter-ionic interactions.

Kohlrausch's Law

For strong electrolytes at low concentrations, the relationship between molar conductivity and concentration can be described by Kohlrausch's Law:

Λm = Λ°m - K√c

Where:
• Λ°m is the Limiting Molar Conductivity (molar conductivity at infinite dilution, where inter-ionic interactions are negligible).
• K is the Kohlrausch constant, which depends on the stoichiometry of the electrolyte and solvent properties.
• c is the molar concentration.
This law shows a linear relationship when Λm is plotted against the square root of concentration (√c). This calculator uses the law to find Λm and then calculates the conductivity κ.

Frequently Asked Questions

Why does Kohlrausch's Law only apply to strong electrolytes?

Kohlrausch's Law is based on the assumption that the electrolyte is fully dissociated into ions at all concentrations considered (which is true for strong electrolytes like NaCl, HCl, MgSO₄). The decrease in molar conductivity with increasing concentration is attributed solely to the increased interactions (like ionic atmosphere drag) between these fully dissociated ions. Weak electrolytes (like acetic acid, CH₃COOH) are only partially dissociated, and their degree of dissociation changes significantly with concentration. This makes their molar conductivity behavior much more complex and non-linear, requiring different models (like Ostwald's Dilution Law).

What are the typical units for conductivity?

• The SI unit for electrical conductivity (κ) is Siemens per meter (S/m).
• However, in chemistry, especially for aqueous solutions, Siemens per centimeter (S/cm) or microsiemens per centimeter (µS/cm) are more commonly used because typical values fall conveniently within these ranges.
• Molar conductivity (Λm) is often reported in S·cm²/mol or the SI unit S·m²/mol (1 S·m²/mol = 10,000 S·cm²/mol).
This calculator allows conversions between common units.

What is Limiting Molar Conductivity (Λ°m)?

Limiting Molar Conductivity (Λ°m) is the theoretical molar conductivity of an electrolyte solution at infinite dilution (concentration approaches zero). At this point, the ions are assumed to be so far apart that they do not interact with each other, and each ion contributes independently to the total conductivity (Kohlrausch's Law of Independent Migration of Ions). Λ°m can be determined experimentally by extrapolating plots of Λm vs. √c back to c=0 for strong electrolytes, or calculated from the limiting ionic conductivities of the individual ions.