1. The problem statement, all variables and given/known data http://i.minus.com/jfUXIXvQJw8hw.png [Broken] 2. Relevant equations Ka of hydrogen sulfate ion will be taken as 1.2x10-2. Ka of ammonium ion will be taken as 5.6x10-10 Kb of ammonia will be taken as 1.8x10-5 Kb of sulfate ion will be taken as something very tiny (Kw/Ka of hydrogen sulfate ion). These values are consistent throughout the literature. 3. The attempt at a solution The reaction of hydrogen sulfate ion and bubbled in ammonia is a large extent reaction. We'll take it as going to completion. Also the pH controlling species here is obviously hydrogen sulfate ion since the magnitude of its Ka is far beyond that of ammonium or ammonia. The problem is that with 0.25 moles of hydrogen sulfate ion left in the system there is NO way there can be a pH of 2.40. A pH of 1.3, yes. It seems that my teacher may have used the natural log instead of the base ten log because taking the natural log of the hydronium ion concentration yields a 2.90 (which may look like 2.40). The pH can easily be ascertained through a simple x^2/Mi = Ka calculation. So am I wrong or is my teacher wrong?