[NewtoAtoms]

Calculate the pH of 0.015 M ammonium Bromide solution

This is my leg work and what I know:

a.  NH4Br <----H20------> NH4+ + Br-
     The Br- is a neutral ion salt
     The NH4+ is an acidic ion, therefore this solution would be slightly acidic

b.  the major species at equillibrium would be NH4Br, NH4+, Br-

c.  Ka = [NH4+][Br-] / [NH4Br]

d. 
                   NH4Br            NH4+      Br-
Initial            0.015             0            0
Change          -x                 +x          +x
--------------------------------------------
Equilibrium    0.015 - x          x             x

therefore

Ka =

• / [0.015-x]

HOWEVER for each question I have solved thus far, I have a value of Ka. However I can't find the Ka of this reaction ANYWHERE.  Can anyone give me assistance on something that I am missing, or not doing correctly.

Thank you for your help and time!

[Astrokel]

As if you would have notice, your ICE table doesn't consist of anything related to [H⁺]/[OH^-] which is required to calculate pH of the solution. Also you have pointed out NH₄⁺ is acidic while Br^- is neutral ion, so which ion will undergo hydrolysis? As your ICE table suggests you considered both ion to undergo hydrolysis. So probably you can guess which K_a value you will used.

[NewtoAtoms]

Okay, that doesn't make a lot of sense to me, but I am going to continue working through the questions to learn, learn, learn..

Therefore I know that the Br- won't affect pH, however NH4+ will.... therefore I must continue the hydrolysis??

NH₄⁺ + H₂0 ----------> NH₃ + H₃0⁺

Ka NH₄⁺ = 5.4 x 10^-10.

therefore:

              NH₄⁺     NH₃     H⁺ (H30+)
Initial      0.15 M     O        O
Change     -x          +x       +x
----------------------------------------
Equili.    0.15 - x      x         x

Ka = [NH₃][H⁺] / [NH₄⁺]
5.4 x 10^-10 = (x)(x) / 0.15 -x

0.15 - x ~ 0.15

5.4 x 10^-10 (0.15) = x²
8.1 x 10^-11 = x²
9.00 x 10^-6 = x

THEREFORE

H⁺ = 9.00 x 10^-6

pH = - log (9.00 x 10^-6)
pH = 5.06

IS THIS LOGIC CORRECT?!?!?
I have just taken your words, tried to understand them and apply them to my question.

Thank you for your time.

[Astrokel]

Your logic and steps are correct, great try! +1 cookie for your good try lol