Molar Conductivity Calculator
Find molar conductivity Λm from specific conductivity and concentration, plus degree of dissociation and Ka.
🔋 What is the Molar Conductivity Calculator?
This molar conductivity calculator finds Λm, an electrolyte's conductivity normalized per mole of dissolved substance, from a measured specific conductivity κ and known concentration c. It also estimates degree of dissociation α and, via Ostwald's dilution law, the dissociation constant Ka when you provide the electrolyte's limiting molar conductivity Λm°.
Molar conductivity measurements are a standard laboratory method for classifying electrolyte strength, checking solution purity, and determining weak acid or base dissociation constants without a full potentiometric titration. An analytical chemistry student measuring how acetic acid's conductivity changes across a dilution series, for instance, is directly applying this calculation to extract Ka.
A common misconception is that molar conductivity is just concentration-adjusted conductivity with no further meaning. In fact, how Λm behaves as concentration changes is itself diagnostic: a strong electrolyte's Λm stays nearly flat across a wide concentration range, while a weak electrolyte's Λm rises sharply on dilution because more molecules dissociate, a distinction visible directly in the chart below.
This calculator is useful for analytical and physical chemistry students, and for chemists characterizing new electrolytes, who need a fast, correct molar conductivity and degree of dissociation without manually applying Ostwald's dilution law.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - 0.1 M KCl (strong electrolyte)
Example 2 - 0.001 M acetic acid (weak electrolyte)
Example 3 - 0.0001 M acetic acid, more dilute
❓ Frequently Asked Questions
🔗 Related Calculators
What is molar conductivity?
Molar conductivity (Lambda_m) is the electrical conductivity of an electrolyte solution divided by its molar concentration, expressed as Lambda_m = 1000 x kappa / c, where kappa is specific conductivity in S/cm and c is concentration in mol/L. It measures how well one mole of dissolved electrolyte conducts electricity.
What is the difference between specific conductivity and molar conductivity?
Specific conductivity (kappa) is a bulk property of the solution measured directly with a conductivity meter, in S/cm. Molar conductivity normalizes that by concentration, letting you compare conducting ability per mole of dissolved substance across different concentrations and electrolytes.
What is Ostwald's dilution law?
Ostwald's dilution law relates the dissociation constant of a weak electrolyte to its degree of dissociation and concentration: Ka = c*alpha^2 / (1 - alpha), where alpha = Lambda_m / Lambda_m° is the fraction of molecules dissociated at that concentration.
Why does molar conductivity increase as concentration decreases?
For a weak electrolyte, dilution shifts the dissociation equilibrium toward more ions (Le Chatelier's principle), increasing the fraction of dissociated molecules. Since more free ions carry more current per mole, molar conductivity rises as concentration falls.
What is degree of dissociation?
Degree of dissociation (alpha) is the fraction of dissolved electrolyte molecules that have actually split into ions, ranging from 0 (no dissociation) to 1 (complete dissociation). It is estimated as alpha = Lambda_m / Lambda_m°, the ratio of measured to limiting molar conductivity.
What is limiting molar conductivity (Lambda_m degree)?
Limiting molar conductivity (Lambda_m°) is the molar conductivity an electrolyte would have at infinite dilution, where ion-ion interactions vanish and (for weak electrolytes) dissociation is essentially complete. It can be measured directly for strong electrolytes or found via Kohlrausch's law for weak ones.
Why is Ka not meaningful for strong electrolytes?
Strong electrolytes are already essentially fully dissociated (alpha close to 1) at all normal concentrations, so the Ostwald dilution law's denominator (1 - alpha) approaches zero, making Ka mathematically undefined or meaningless. Strong electrolytes simply do not have a meaningful dissociation equilibrium constant.
What units are used for molar conductivity?
Molar conductivity is most commonly reported in S·cm²/mol (siemens times square centimetres per mole), which follows directly from specific conductivity in S/cm divided by concentration in mol/cm3, scaled by the 1000 factor when concentration is given in mol/L.
How is molar conductivity related to Kohlrausch's law?
Kohlrausch's law predicts the limiting molar conductivity Lambda_m° of an electrolyte from its individual ionic conductivities, or models how Lambda_m approaches Lambda_m° as concentration falls for a strong electrolyte. Use the Kohlrausch Law Calculator once you have Lambda_m° to explore that behavior further.
Can molar conductivity be used to identify an unknown electrolyte's strength?
Yes. Measuring Lambda_m across several concentrations and observing whether it stays nearly flat (strong electrolyte) or rises sharply with dilution (weak electrolyte) is a classic experimental method for classifying an electrolyte's dissociation behavior.