posted by John Gold on .
A technician requires a 4L of an ammonia solution to have a pH of 11.55. What volume in liters, of ammonia gas at 25 degrees Celsius and 1 atm is necessary to achieve this result?
NH3 + HOH ==> NH4^+ + OH^-
Kb = (NH4^+)(OH^-)/(NH3)
You want pH = 11.55 so pOH is 14-11.55 = ??. Convert pOH to OH^-, substitute for (OH^-) and for (NH4^+) in the Kb expression, and solve for NH3. That will give you (NH3) in moles/L. You will want 4 times that to make a 4 L solution, then plug those moles into PV = nRT and solve for volume at the conditions listed.