Imagine we have a solution with 0.090 mol of NH4Cl dissolved in an open beaker(remaining solution composition, if needed, is as follows: 0.003 mol of MgCl2.6H2O, 0.054 mol of KCl 0.016 mol of Na2SO4 0.079 mol of NaCl and 0.003 mol of CaCl2)
Consider we need to increase the pH of solution from ~6 to 8.5. Will the amount of NH3 escaping from solution be significant so that when we decrease pH back to 6 the amount of NH4 in solution will be much lower that the one in the beginning? can we estimate the amount of NH3 expecting to evolve from solution?
Dear Denis Rodrigues, you could measure the NH4+ concentration before and after the pH readjustment and the difference would be the amount of ammonia released:
Milimoles of NH3 = M1V1 - M2V2
Where:
M1 and M2: the molarities de NH4+ before (1) and after (2) readjusting the pH.
V1 and V2: the total volumes (mL) of solution before (1) and after (2) readjusting the pH.
It would be necessary to select a method to analytically determine ammonium. Initially I think of a potentiometric titration with NaOH or, failing that, a manual titration with a suitable indicator.
Postscript: it would be necessary to know how you´ll adjust the pH to 8.5 and back to 6, to evaluate if it is feasible to apply the acid-base titration.
pH adjustment would be through NaOH addition. Forgot to mention that.
Regarding the significance of the amount of volatilized ammonia, some important variables may affect: exposure time at a pH of 8.5. if there will be heating or agitation. By the way, assuming that you have 1 L of solution, the NH4+/NH3 ratios are 1800 and 5.7 at pH of 6 and 8.5, respectively.
I gather that the relative concentration of ammonia in solution is important. Why not add ammonium hydroxide to adjust the pH?
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