Difference between revisions of "Ionic Strength"

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(Converting from Mole fraction to Molal-based units)
(Converting from Mole fraction to Molal-based units)
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Where:
 
Where:
  
I(m)      = ionic strength in molal-based units
+
I(m)      = ionic strength in molal-based units <br>
I(x)      = ionic strength in mole fraction-based units
+
I(x)      = ionic strength in mole fraction-based units<br>
LIQMOL    = moles of liquid (true species)
+
LIQMOL    = moles of liquid (true species)<br>
gmole H2O = moles of water in the liquid phase (true species)
+
gmole H2O = moles of water in the liquid phase (true species)<br>
  
  
  
 
[[user:DMILLER | Author: Diana Miller]]
 
[[user:DMILLER | Author: Diana Miller]]

Revision as of 05:57, 7 September 2022

Ionic Strength (molal based or m-based)

The ionic strength is a quantity representing the strength of the electric field in a solution, and it is equal to the sum of the molalities of each type of ion present multiplied by the square of their charges, as represented by the following equation:

Ionic molal based1.png

Where n is the number of charged species.


For example, a 1.0 molar solution of NaCl has 1.0 moles of Na^+ions and 1.0 moles of Cl^- ions in 1 kg of H2O. Therefore, the ionic strength is 1.0 molal.


Molal based2.png


Now, consider a 1.0 molal solution of CaCl2. This solution has 1.0 moles of Ca^(+2) ions and 2.0 moles of Cl^- ions in 1 kg of H2O. Therefore, the ionic strength is 3.0 molar, or it can be said that a 1.0 molal solution of CaCl2 behaves similar to a 3.0 molar solution of NaCl.

Numbers molal based.png

Ionic Strength (mole fraction based or x-based)

In this case the ionic strength is calculated using the mole fraction rather than the molality:

Mass fraction based.png


Where n is the number of charged species.


Converting from Mole fraction to Molal-based units

The equation to use is the following:

I(m) = I(x) x LIQMOL / gmole H2O x 55.5082

Where:

I(m) = ionic strength in molal-based units
I(x) = ionic strength in mole fraction-based units
LIQMOL = moles of liquid (true species)
gmole H2O = moles of water in the liquid phase (true species)


Author: Diana Miller