How do I determine the cell constant of a conductivity cell?

Immerse the cell in a KCl standard of known conductivity, read the conductance G (or resistance R = 1/G) and compute K_cell = κ_standard/G. Common 25 °C values are 147 μS/cm for 0.001 mol/L, 1413 μS/cm for 0.01 mol/L, 12.88 mS/cm for 0.1 mol/L and 111.9 mS/cm for 1 mol/L KCl. If you calibrate away from 25 °C, convert the standard's conductivity to the measurement temperature first (about 1.9%/°C for KCl). Choose a standard close to your samples' conductivity.

What is the difference between conductivity and molar conductivity?

Conductivity κ is the conductance of a 1 cm cube of solution, in S/cm, and rises with concentration. Molar conductivity Λm = κ/c is the conductance of one mole of electrolyte between electrodes 1 cm apart, in S·cm²/mol, and reflects how well each ion carries current. Because of ion–ion interactions Λm of a strong electrolyte falls slowly with concentration, while for a weak electrolyte it falls steeply as the degree of dissociation decreases.

How is the dissociation constant of acetic acid found from conductivity?

Measure κ of an acetic acid solution and compute Λm = 1000κ/c. The limiting value from independent ionic migration is Λm°(HAc) = 349.6 + 40.9 = 390.5 S·cm²/mol. Then α = Λm/Λm° and Ka = cα²/(1 − α). For 0.01 mol/L with κ = 163 μS/cm, α ≈ 0.042 and Ka ≈ 1.8 × 10⁻⁵. With a concentration series, plot 1/Λm against cΛm: the intercept is 1/Λm° and the slope gives Ka.

Why is a conductometric titration curve V-shaped?

When NaOH titrates HCl, the solution initially conducts mainly through the very mobile H⁺ ion (λ° = 349.6). Added NaOH replaces H⁺ with the slower Na⁺ (50.1), so conductivity falls linearly; after the equivalence point excess OH⁻ (199.1) makes it rise again, and the intersection of the two lines is the end point. A weak acid starts low and rises slowly, and the KCl + AgNO₃ precipitation titration is almost flat before the end point. Conductometric titration works for coloured, turbid or very dilute solutions.

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🔌Conductivity Calculator - Cell Constant, Molar Conductivity, Kohlrausch's Law & Titration

Electrolytic conductivity is a basic quantity in physical chemistry labs and water analysis. A conductivity meter measures conductance G (or resistance R); multiplying by the cell constant K_cell = l/A gives the conductivity κ. The cell constant is calibrated with a KCl standard of known conductivity — at 25 °C 0.01 mol/L KCl has κ = 1413 μS/cm, so a reading of 1.413 mS means K_cell = 1.000 cm⁻¹. Molar conductivity is Λm = κ/c, or Λm = 1000κ/c in S·cm²/mol with κ in S/cm and c in mol/L. Strong electrolytes follow Kohlrausch's square-root law Λm = Λm° − K√c, so a straight-line extrapolation of dilute data gives the limiting molar conductivity: with the built-in CRC Handbook KCl data up to 0.01 mol/L the intercept is 149.6, against the literature 149.86 S·cm²/mol. By the law of independent migration of ions Λm° is the sum of the ionic contributions, e.g. Λm°(HAc) = λ°(H⁺) + λ°(CH₃COO⁻) = 349.6 + 40.9 = 390.5 S·cm²/mol, which also equals Λm°(HCl) + Λm°(NaAc) − Λm°(NaCl); the transport number is t₊ = λ₊/Λm°. For a weak electrolyte the degree of dissociation is α = Λm/Λm° and Ostwald's dilution law gives Ka = cα²/(1 − α): 0.01 mol/L acetic acid with κ = 163 μS/cm has Λm = 16.3, α = 0.0417 and Ka ≈ 1.8 × 10⁻⁵. The calculator also computes conductometric titration curves (strong acid–strong base, weak acid–strong base, mixed acids and AgNO₃ precipitation, with dilution correction) from ionic conductivities and the charge balance, finds the end point of your own data from two intersecting lines, and converts water EC to 25 °C, TDS and resistivity (ultrapure water 18.2 MΩ·cm).

Free · No sign-up · Runs in your browserLast updated: 2026-10-29

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How to use Conductivity Calculator

1Choose a mode: cell constant, molar conductivity, Kohlrausch's law, weak electrolyte Ka, conductometric titration or water quality
2Enter meter readings, concentrations and temperatures, or load the built-in KCl/NaCl literature data and simulated examples
3Read the worked steps, fitted lines and charts, copy results or export PNG, SVG and CSV

FAQ

How do I determine the cell constant of a conductivity cell?: Immerse the cell in a KCl standard of known conductivity, read the conductance G (or resistance R = 1/G) and compute K_cell = κ_standard/G. Common 25 °C values are 147 μS/cm for 0.001 mol/L, 1413 μS/cm for 0.01 mol/L, 12.88 mS/cm for 0.1 mol/L and 111.9 mS/cm for 1 mol/L KCl. If you calibrate away from 25 °C, convert the standard's conductivity to the measurement temperature first (about 1.9%/°C for KCl). Choose a standard close to your samples' conductivity.
What is the difference between conductivity and molar conductivity?: Conductivity κ is the conductance of a 1 cm cube of solution, in S/cm, and rises with concentration. Molar conductivity Λm = κ/c is the conductance of one mole of electrolyte between electrodes 1 cm apart, in S·cm²/mol, and reflects how well each ion carries current. Because of ion–ion interactions Λm of a strong electrolyte falls slowly with concentration, while for a weak electrolyte it falls steeply as the degree of dissociation decreases.
How is the dissociation constant of acetic acid found from conductivity?: Measure κ of an acetic acid solution and compute Λm = 1000κ/c. The limiting value from independent ionic migration is Λm°(HAc) = 349.6 + 40.9 = 390.5 S·cm²/mol. Then α = Λm/Λm° and Ka = cα²/(1 − α). For 0.01 mol/L with κ = 163 μS/cm, α ≈ 0.042 and Ka ≈ 1.8 × 10⁻⁵. With a concentration series, plot 1/Λm against cΛm: the intercept is 1/Λm° and the slope gives Ka.
Why is a conductometric titration curve V-shaped?: When NaOH titrates HCl, the solution initially conducts mainly through the very mobile H⁺ ion (λ° = 349.6). Added NaOH replaces H⁺ with the slower Na⁺ (50.1), so conductivity falls linearly; after the equivalence point excess OH⁻ (199.1) makes it rise again, and the intersection of the two lines is the end point. A weak acid starts low and rises slowly, and the KCl + AgNO₃ precipitation titration is almost flat before the end point. Conductometric titration works for coloured, turbid or very dilute solutions.

Features

Cell constant calibration with 0.001–1 mol/L KCl standards from conductance or resistance readings
Linear temperature compensation to 25 °C with an adjustable coefficient (default 2%/°C)
Molar conductivity with S·cm²/mol and S·m²/mol unit conversion
Kohlrausch Λm vs √c regression to Λm°, with KCl and NaCl literature data built in
Limiting ionic conductivities of 16 ions at 25 °C; build any electrolyte to get Λm° and transport numbers
Degree of dissociation and Ka of weak electrolytes from one measurement or an Ostwald plot
Conductometric titration curves for strong, weak and mixed acids and precipitation, with per-ion contributions and two-line end-point detection
Water quality: EC₂₅, TDS, resistivity and ISO 3696 laboratory water grade

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