Question

we consider an ammonium solution with a concentration of 0.05 mol / L
1) Write the equation of acidic basic equilibrium between NH4 + ammonium ions and water
2) Express literally the acidity constant KA of this equation.
3) Make the progress table showing the progress of the reaction x and give the expression of the acidity constant KA as a function of x.
4) Establish the second degree equation to determine the concentration of H3O + ions
5) Calculate this concentration then give the ph

We give pka (NH4 + / NH3) = 9.2

Answer 1

Ans) 1) The equation for ammonium ion solution in water will be :-

              

        2) K_a for the above dissociation reaction is given as :-

              

        3)   The progress of the reaction can be shown in the following manner:-

Initially: C=0.05                                   

    At Equi. :   0.05 - x                         x             x                         Where    or

              Expression for K_a will be :-

                      

        4) The second degree equation can be easily obtained from the above expression for K_a :-

                    

                    

            This is the required equation and as we know from above reaction progress that x = [H₃O⁺].

        5) Given, P_Ka for the acid is 9.2

               

               

               

           Substituting the value of K_a to find the value of x,

            

           To calculate for x , we need to find the values for:-

           

           

           The correct positive solution from this equation comes out to be :-

           

           Since, x = [H₃O⁺] , thus the pH of the solution will be:-

           

                [Answer]