Question

Consider \(0.25 M\) solutions of the following salts: \(\mathrm{NaCl}\), \(\mathrm{RbOCl}, \mathrm{KI}, \mathrm{Ba}\left(\mathrm{ClO}_{4}\right)_{2}\), and \(\mathrm{NH}_{4} \mathrm{NO}_{3} .\) For each salt, indicate whether the solution is acidic, basic, or neutral.

Short answer

In conclusion, the solutions of the given salts have the following properties: \(\mathrm{NaCl}\) (neutral), \(\mathrm{RbOCl}\) (basic), \(\mathrm{KI}\) (neutral), \(\mathrm{Ba}(\mathrm{ClO}_{4})_{2}\) (neutral), and \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) (acidic). This is based on whether each salt dissociates into strong or weak acids and bases in the solution.

Step-by-step solution

1. Analyze NaCl

NaCl is formed from the strong acid HCl and the strong base NaOH. When NaCl dissociates in water, it forms Na+ and Cl- ions. Since both the acid and base are strong, the solution will be neutral.

2. Analyze RbOCl

RbOCl is formed from the strong base RbOH and the weak acid HOCl. When RbOCl dissociates in water, it forms Rb+ and OCl- ions. Since the base is strong and the acid is weak, the solution will be basic.

3. Analyze KI

KI is formed from the strong acid HI and the strong base KOH. When KI dissociates in water, it forms K+ and I- ions. Since both the acid and base are strong, the solution will be neutral.

4. Analyze Ba(ClO4)2

Ba(ClO4)2 is formed from the strong acid HClO4 and the strong base Ba(OH)2. When Ba(ClO4)2 dissociates in water, it forms Ba2+ and 2 ClO4- ions. Since both the acid and base are strong, the solution will be neutral.

5. Analyze NH4NO3

NH4NO3 is formed from the weak base NH3 and the strong acid HNO3. When NH4NO3 dissociates in water, it forms NH4+ and NO3- ions. Since the base is weak and the acid is strong, the solution will be acidic. In conclusion, the solutions of NaCl, KI and Ba(ClO4)2 are neutral, the solution of RbOCl is basic and the solution of NH4NO3 is acidic.

Key concepts

Salt Dissociation

When salts dissolve in water, they undergo a process known as dissociation. This means that the salt separates into its individual ions. For example, when sodium chloride (NaCl) is added to water, it dissociates into sodium ions (Na⁺) and chloride ions (Cl^-).

The extent of dissociation and the resulting pH of the solution largely depend on the nature of the ions. If the ions come from a strong acid and a strong base, like in the case of NaCl, the solution is typically neutral.

• Salts of strong acids and strong bases usually form neutral solutions.
• Salts from strong bases and weak acids generally lead to basic solutions.
• Salts from strong acids and weak bases often result in acidic solutions.

Acid-Base Strength

The strength of an acid or base is determined by its ability to ionize or dissociate in water. Strong acids and bases completely dissociate, making them more effective at altering the pH of a solution.

• Strong acids like hydrochloric acid (HCl) fully dissociate in water, providing a significant increase in hydronium ions (H₃O⁺), leading to a lower pH.
• Strong bases such as sodium hydroxide (NaOH) fully dissociate to give hydroxide ions (OH^-), raising the pH.
• Weak acids and bases only partially dissociate, resulting in a less dramatic effect on the solution's pH.

Understanding this concept helps in predicting the acidity, basicity, or neutrality of a salt solution.

Acidic Solutions

A solution is acidic if it has a greater concentration of hydronium ions (H₃O⁺) compared to hydroxide ions (OH^-). This occurs when a salt is derived from a strong acid and a weak base.

For example, when ammonium nitrate ( ext{NH}₄ ext{NO}₃) dissolves in water, it produces ammonium ions ( ext{NH}₄⁺) and nitrate ions ( ext{NO}₃^-). The ammonium ion ( ext{NH}₄⁺) can donate a hydrogen ion to water, forming an acidic solution:

• Ammonium is from the weak base ammonia, which influences the acidic nature.
• Since nitric acid is strong, the nitrate ion doesn't affect the pH.

This results in an increased concentration of H₃O⁺, thus producing an acidic solution.

Neutral Solutions

Neutral solutions occur when the concentrations of hydronium ions (H₃O⁺) and hydroxide ions (OH^-) are equal. Salts formed from both strong acids and strong bases are typically neutral.

Examples like sodium chloride ( ext{NaCl}, formed from HCl and NaOH) and potassium iodide ( ext{KI}, formed from HI and KOH) illustrate this concept. These salts dissociate completely in water, but neither the cations nor the anions react further to alter the pH:

• When a salt derived from a strong acid and a strong base dissolves, the resultant solution tends to remain neutral, with a pH close to 7.

This happens because the ions involved do not contribute additional H₃O⁺ or OH^- ions to the water.

Basic Solutions

Solutions become basic when they contain more hydroxide ions (OH^-) than hydronium ions (H₃O⁺). This is common for salts derived from strong bases and weak acids.

A salt like rubidium hypochlorite ( ext{RbOCl}) demonstrates this. Formed from RbOH (a strong base) and HOCl (a weak acid), it dissociates in water to release Rb⁺ and OCl^- ions:

• The hypochlorite ion (OCl^-) acts as a weak base in solution.
• Since RbOH is strong, the resultant solution is basic due to the dominance of OH^- formation from OCl^-.

Thus, the presence of OCl^- increases the OH^- concentration, shifting the solution to a basic pH range.