Huckels law validity and comparison with experimental data

Debye and Huckel s law validity and comparison with experimental data 

Experience tells us that ionic solutions only behave like ideal dilute solutions y+ = 1) below a concentration of 10 moles per liter, whereas for a molecular solution, such behavior is acceptable below 10 moles per liter. 

In practice, we consider that Debye and Huckel s law, expressed by relation [4.82], and in particular using its form [4.88] in water, can only be used for solutions in which the ionic strength is no greater than lO mol/1, although in certain cases, ionic strengths of lO mol/l can also yield acceptable results. Certain authors prefer to adjust the law [4.82] by adjusting two experimental conditions  

By this method, we are able to apply the formula [4.82] to a broader range of ionic strengths. However, the values thus determined for a still need to be acceptable in terms of the physical meaning. Indeed, certain experiments yield very low values of the radius a - sometimes zero, and sometimes even negative values are required. The true value of a must be no lower than the ionic radius determined in a crystal of a corresponding salt. 

Nevertheless, let us remember that Debye and Hiickel s law supposes the ions are spherical, which can be accepted for sufficiently dilute solutions in which the radius of the ionic atmosphere is larger than a and therefore in which the ions are relatively far removed from one another. If the ions come closer together, the hypothesis of sphericity becomes trickier to accept for a large number of t5q)es of ions - particularly for polyatomic ions. 

---