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Debye–Hückel Limiting Activity Coefficient

Estimate a single-ion activity coefficient in a very dilute solution using an entered solvent-dependent constant.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

The limiting model approaches coefficient 1 as ionic strength approaches zero.

log10(gamma) = −A z² sqrt(I)

Worked example

Enter these known values and leave the other values blank.

Charge number of ion (z)
1
Ionic strength (I)
0 M
Activity coefficient (f)
1

Assumptions and limitations

  • The limiting law is a dilute-solution approximation. The default A=0.509 corresponds approximately to aqueous solution at 25 °C with the appropriate concentration convention; ionic strength must use the convention behind A.
  • Individual-ion activity coefficients use a convention. This tool does not implement finite-ion-size, Davies or concentrated-electrolyte models.

Common questions

What does this model assume?

The limiting law is a dilute-solution approximation. The default A=0.509 corresponds approximately to aqueous solution at 25 °C with the appropriate concentration convention; ionic strength must use the convention behind A.

Can I solve backward?

Clear the unknown value and enter compatible known values. Choices, one-way outputs and singular boundary cases cannot always be inverted.

References

Explicit physical and mathematical model domains: finite positive denominators, dilute limiting-law applicability, integral ionic charge numbers, nonnegative concentrations and normalized isotope abundances.

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