It has been found that the pH of a 0.01 M solution of an organic acid is 4.15. Calculate the concentrationof the anion, the ionizationconstant of the acid and its pK_a.

It has been found that the pH of a 0.01 M solution of an organic acid

1.	It has been found that the pH of a 0.01 M solution of an organic acid is 4.15. Calculate the concentrationof the anion, the ionizationconstant of the acid and its pK_a.
Answer» Solution :Calculationof `H^+` :pH=-LOG `[H^+]`= -4.15 = `bar5.85` `therefore [H^+]`= Antilog `(bar5.85)=7.079xx10^(-5)` Calculation of ionization constant `K_a` : `{:("WEAK acid :",HA hArr, H^(+)+,A^-),("Initial M:",0.01,0,0),("EQUILIBRIUM M:",(0.01-x), x,x):}` So, `[H^+]=[A^-]=7.079xx10^(-5)=x` [HA]=(0.01 -x) `APPROX` 0.01 (because `0.01 GT gt gt x`) `K_a` `=([H^+][A^-])/([HA])` `=((7.079xx10^(-5))(7.079xx10^(-5)))/0.01` `=5.011xx10^(-7)` Calculation of `pK_a` : `pK_a=-log K_a` `=-log (5.011xx10^(-7))` =-(0.6999-7)=-(-6.30)=+6.30