Question

The ph of aqueous ammonia is 11.5. find the molarity

Answer 1

pH = 11.50 
pOH = 2.50 
[OH-] = 0.00316 M 

A bottle labeled "ammonium hydroxide" contains very little in the way of ammonium or hydroxide ions and no molecules of NH4OH. In fact, the solution in the bottle is mostly aqueous ammonia. 

NH3(aq) + HOH(l) <==> NH4+ + OH- ..... Kb = 1.8x10^-5 
?M ........................... .0.00316M...0.00316M 

Kb = [NH4+] [OH-] / [NH3] 
[NH3] = Kb / ([NH4+] [OH-]) 
[NH3] = 1.8x10^-5 / (0.00316)² 
[NH3] = 1.8 M