Weak acid and base calculations

Question

How many grams of ammonia must be added to water to make one leader of an ammonia solution with a pH of 11.81

Answer 1

Hi Zoey, For solutions of weak bases, you don't have to go the whole ICE table route. You can just use the approximation of pOH = sqrt(Kb[B]) where: sqrt() is the square root Kb is the base dissociation constant (which you will have to look up) [B] is the initial concentration of the weak base, which is ammonia in this problem. Since the target pH is 11.81, the pOH = 14 - 11.81, or pOH = 2.19. Once you get the concentration of ammonia, you can calculate the moles of ammonia based on the volume (I assume it is 1 L). Then from moles, use the molar mass of ammonia to calculate the grams. Jim S.