Question

A treatment plant has the following species in the influent wastewater: NH3-N = 24 mg-N/L, 0.13 mg NO2-N/L, 0.41 mg NO3-N/L, and a pH of 7. Using MINEQL+5.0 available on the COE computers generate a single pC-pH diagram showing the species, NH4+, NH3(aq), NO2-, NO3-, H+ and OH- as a function of pH (from 0.5 to 13.5 in 26 steps). Answer the following question, which nitrogen species is predominating at pH 6 and which is predominating at pH 11?

Answer 1

In this question, we have to answer that which nitroen species is dominant at pH 6 and pH 11 out of the given species.

Let us contemplate the given pH values first. At pH 6 we can say that the given species or ion will be near to the neutral nature as water is neutral or any speicies is neutral at pH 6 or slightly acidic. Thus NH₄⁺ can be considered as slightly acidic species and will be predominant at pH 6.

Now NH₃ is considered as the basic species becuase its pKa is near about 33 which is categorized as highly basic. Moroever it has the ability to abstract acidic protons from the species. Thus NH₃ will be predominant at pH 11.