Question

Posted by Cyndy on Sunday, February 15, 2015 at 6:45pm.


How many grams of ammonium chloride are needed to raise the ammonia level 5 ppm in a 300 gallon system?
Now,
I have worked the problem so many times I have confused myself I think.
I keep getting 2 different answers depending upon how I work the question.
Idk if it's 5.6775 grams of NH4Cl or 16.82811 grams of NH4Cl since it takes 2.964 units of NH4CL to equal a 100% Ammonium solution

Answer 1

The way I read the problem it is a hydrolysis problem.
NH4^+ + H2O ==> NH3 + H3O^+
and you want the NH3 (ammonia, not ammonium) to be 5 ppm. Note that 5 ppm is 5E-3g/L and convert to mol/L and work the problem to see M NH4Cl. Then convert that to g NH4Cl in 300 gallons. The number you get for this seems excessively large but I think it is right; i.e., if you go at it another way and calculate the pH of that solution it gives you the right pH. That may be the point of the problem; i.e., to show you just how much it takes to raise the NH3 level as little as 5 ppm.