Question

what is ostald dilution law

Answer 1

Ostwald’s dilution law is the application of the law of mass action to weak electrolytes in solution. Suppose an acid HA is dissolved in water, it will ionise as under:



Applying law of mass action,



Where  is the dissociation (or ionisation) constant of the acid HA and  is its degree of dissociation.

This equation is known as Ostwald’s dilution law equation. If   then the above equation may be written as:



Thus at constant temperature degree of dissociation of weak electrolyte is directly proportional to square root of its dilution. The value of  can be calculated by measuring conductance of the solution as:



 

Where is the equivalent conductance at a particular dilution and  is equivalent conductance at infinite dilution.

With the help of this equation;  or of the acid solution may be calculated.

If we know the value of and C for any acid then may be calculated. For example, the value of for 0.05 N acetic acid is 0.03.

Therefore the value of   for acetic acid will be,



Weak electrolytes obey Ostwa1d’s dilution law fairly well, but strong electrolytes do not obey this law; because these electrolytes almost completely ionise at every concentration i. e. ,  , but in practice it is not so. thus  is not applicable for strong electrolytes. It is observed that even though .

Answer 2

Wilhelm Ostwald's dilution law is a relationship proposed in 1888 between the dissociation constant Kd and the degree of dissociation α of a weak electrolyte. The law takes the form. Where the square brackets denote concentration, and c0 is the total concentration of electrolyte.