The pH of an aqueous ammonium nitrate (NH4NO3) solution is because . Group of answer choices about 7; ammonium is a weak acid, but produces ammonia, and these two neutralize one another 0; ammonium nitrate is a salt, not an acid or a base 7; ammonium nitrate is a simple salt above 7; nitrate is a weak base below 7; ammonium is a weak acid
The Correct Answer and Explanation is:
Correct Answer: below 7; ammonium is a weak acid
Explanation:
Ammonium nitrate (NH₄NO₃) is a salt formed from the neutralization of a strong acid (nitric acid, HNO₃) and a weak base (ammonia, NH₃). When this salt dissolves in water, it dissociates into NH₄⁺ (ammonium ion) and NO₃⁻ (nitrate ion).
- NH₄⁺ (ammonium ion) is the conjugate acid of ammonia (a weak base). It can donate a proton (H⁺) in water, making the solution slightly acidic.
- NO₃⁻ (nitrate ion) is the conjugate base of nitric acid, a strong acid. Since strong acids dissociate completely, their conjugate bases are very weak and do not affect the pH.
Thus, the ammonium ion can undergo hydrolysis in water: NH4++H2O→NH3+H3O+\text{NH}_4^+ + \text{H}_2\text{O} \rightarrow \text{NH}_3 + \text{H}_3\text{O}^+NH4++H2O→NH3+H3O+
This reaction increases the concentration of H₃O⁺ ions, making the solution acidic.
Because only the ammonium ion reacts with water and not the nitrate ion, the net effect is an acidic solution, so the pH is below 7.
This behavior is typical of salts formed from a strong acid and a weak base. The weak base does not neutralize the acid completely in terms of pH effect, so the resulting solution is acidic.
Therefore, the best choice that matches both the chemical understanding and the answer format is:
“below 7; ammonium is a weak acid”.
