What is the calculation principle for the determination of free ammonia?
Thread Content
This post was last edited by chen3jun on 2009-12-12 20:48. When titrating free ammonia in a solution with sulfuric acid, the following reactions mainly occur. 2NH4OH + H2SO4 == (NH4)2SO4 + 2H2O. 2NH4HCO3 + H2SO4 == (NH4)2SO4 + 2CO2↑ + 2H2O. (NH4)2CO3 + H2SO4 == (NH4)2SO4 + CO2↑ + H2O. When performing calculations, the ammonia content in the solution is determined based on the amount of sulfuric acid used. However, in these three reactions, sulfuric acid does not react in a 1:1 molar ratio with free ammonia; that is to say, the consumption of one mole of sulfuric acid does not necessarily mean that there is one mole of free ammonia in the solution. May I ask what the basis for the calculation is?
This post was last edited by chen3jun on 2009-12-13 21:02. Why isn’t anyone offering to help? I thought about it for a while ； The ammonia-alkali reaction can be simplified as: 2(NH4+) + SO42- → (NH4)2SO4. Thus, for every 1 mol of sulfuric acid consumed, 2 mol of ammonium ions are used
What standard is this based on? Of these reactions, the first one is the reaction between ammonia and sulfuric acid; the subsequent reactions involve carbonate, bicarbonate, and sulfuric acid. If the concentrations of the latter two substances are not known, how can the concentration of free ammonia be calculated?
This post was last edited by xwtsq on 2009-12-15 08:17. May I ask the original poster: does the free ammonia you mentioned include NH4OH, NH4HCO3, and (NH4)2CO3? The principle behind the calculation is actually quite simple; once you understand the rule of equal amounts of substance, it will become clear. Since the basic unit of the sulfuric acid standard titrant you are using is 1/2H2SO4, 1 mole of 1/2H2SO4 is equivalent to 1 mole of NH4+.
I think the original poster didn’t clarify the question properly.