Question

Ammonia nitrogen is present in a given wastewater sample as the ammonium ion (\( \text{NH}_4^+ \)) and ammonia (\( \text{NH}_3 \)). If pH is the only deciding factor for the proportion of these two constituents, which of the following is a correct statement?

• A. At pH above 9.25, only \( \text{NH}_4^+ \) will be present.
• B. At pH below 9.25, \( \text{NH}_3 \) will be predominant.
• C. At pH 7.0, \( \text{NH}_4^+ \) and \( \text{NH}_3 \) will be found in equal measures.
• D. At pH 7.0, \( \text{NH}_4^+ \) will be predominant.

Hint:

The ratio of ammonium ion (\( \text{NH}_4^+ \)) and ammonia (\( \text{NH}_3 \)) depends on the pH, with \( \text{NH}_4^+ \) being predominant at lower pH and \( \text{NH}_3 \) at higher pH.

Answer 1

The Correct Option is D

The proportion of ammonium ion (\( \text{NH}_4^+ \)) and ammonia (\( \text{NH}_3 \)) in wastewater depends on the pH level. As the pH increases, the equilibrium between \( \text{NH}_4^+ \) and \( \text{NH}_3 \) shifts, with more ammonia (\( \text{NH}_3 \)) forming as pH rises. At pH 7.0, the equilibrium favors the ammonium ion (\( \text{NH}_4^+ \)) more than ammonia (\( \text{NH}_3 \)), making \( \text{NH}_4^+ \) the predominant species at this pH. Final Answer: \[ \boxed{\text{(D) At pH 7.0, } \text{NH}_4^+ \text{ will be predominant.}}. \]