- Categorize each reactant as a strong or weak acid or base using the provided table.
- Determine the nature of the resulting salt for each reaction: strong acid + weak base = acidic (pH < 7), weak acid + strong base = basic (pH > 7), strong acid + strong base = neutral (pH ≈ 7).
- Identify that only the \(NH_3 + HNO_3\) reaction consists of a weak base and a strong acid.
- Conclude that the salt from the \(NH_3 + HNO_3\) reaction has a \(\boxed{pH < 7}\). Final answer is \(\boxed{NH_3 + HNO_3}\).
Explanation
- Principles of Acid-Base Neutralization
To determine which reaction yields a salt with a pH < 7, we analyze the strength of the acid and base involved in each neutralization reaction. Neutralization reactions follow specific patterns regarding the pH of the resulting salt solution:
- A reaction between a strong acid and a strong base produces a neutral salt, resulting in a pH ≈ 7.
- A reaction between a strong acid and a weak base produces an acidic salt, resulting in a pH < 7.
- A reaction between a weak acid and a strong base produces a basic salt, resulting in a pH > 7.
Based on the provided table:
- Strong acids include HBr, \(HNO_3\), and \(H_2SO_4\).
- Strong bases include NaOH, KOH, and \(Ca(OH)_2\).
- Weak acids include \(CH_3COOH\) and HCOOH.
- Weak bases include \(NH_3\) and \(NH_4OH\).
- Analyzing Each Reaction
Now, let's categorize each of the given reactions based on the strengths of the reactants:
- \(KOH + HBr\): KOH is a strong base and HBr is a strong acid. Their neutralization produces a neutral salt (pH ≈ 7).
- \(HCOOH + KOH\): HCOOH is a weak acid and KOH is a strong base. Their neutralization produces a basic salt (pH > 7).
- \(Ca(OH)_2 + H_2SO_4\): \(Ca(OH)_2\) is a strong base and \(H_2SO_4\) is a strong acid. Their neutralization produces a neutral salt (pH ≈ 7).
- \(NH_3 + HNO_3\): \(NH_3\) is a weak base and \(HNO_3\) is a strong acid. Their neutralization produces an acidic salt, which results in a pH < 7.
- Conclusion
Comparing the results from our analysis, only the reaction between \(NH_3\) (a weak base) and \(HNO_3\) (a strong acid) leads to a salt solution with a pH < 7. Therefore, the correct reaction is \(NH_3 + HNO_3\). The final answer is \(\boxed{NH_3 + HNO_3}\).
Examples
In real-world applications, understanding the pH of salt solutions is crucial in fields like agriculture and water treatment. For instance, if soil is too basic, farmers may add ammonium-based fertilizers (which are acidic) to balance the soil pH, as these compounds can slightly lower the pH through hydrolysis. Understanding whether a reaction produces an acidic, basic, or neutral salt allows for precision in controlling chemical environments in everything from laboratory experiments to industrial manufacturing processes.