Question

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

Short answer

In summary, the solutions of the salts have the following properties: NaCl and KI are neutral, RbOCI and Ba(ClO2)2 are basic, and NH4NO3 is acidic.

Step-by-step solution

Examine the cations and anions in each salt

To determine the nature of each salt, we need to examine the cations and anions involved. The salts given are: 1. NaCl: Cation: Na+, Anion: Cl- 2. RbOCI: Cation: Rb+, Anion: OCl- 3. KI: Cation: K+, Anion: I- 4. Ba(ClO2)2: Cation: Ba2+, Anion: ClO2- 5. NH4NO3: Cation: NH4+, Anion: NO3-

Determine the nature of cations and anions in each salt

For each salt, we will analyze the cations and anions and predict their behavior in water. 1. NaCl: Na+ is a neutral cation (from a strong base, NaOH), Cl- is a neutral anion (from a strong acid, HCl) 2. RbOCI: Rb+ is a neutral cation (from a strong base, RbOH), OCl- is a basic anion (from a weak acid, HOCl) 3. KI: K+ is a neutral cation (from a strong base, KOH), I- is a neutral anion (from a weak acid, HI) 4. Ba(ClO2)2: Ba2+ is a neutral cation (from a strong base, Ba(OH)2), ClO2- is a basic anion (from a weak acid, HClO2) 5. NH4NO3: NH4+ is an acidic cation (from a weak base, NH4OH), NO3- is a neutral anion (from a strong acid, HNO3)

Categorize the solutions based on cations and anions behavior

Using the predicted behavior of the cations and anions in water, we can categorize the solutions in terms of acidity or basicity. 1. NaCl: Neutral solution (neutral cation and neutral anion) 2. RbOCI: Basic solution (neutral cation and basic anion) 3. KI: Neutral solution (neutral cation and neutral anion) 4. Ba(ClO2)2: Basic solution (neutral cation and basic anion) 5. NH4NO3: Acidic solution (acidic cation and neutral anion) In conclusion, the solutions of NaCl and KI are neutral, the solutions of RbOCI and Ba(ClO2)2 are basic, and the solution of NH4NO3 is acidic.

Key concepts

Acidic Solutions

An acidic solution occurs when the concentration of hydrogen ions (H⁺) surpasses that of hydroxide ions (OH⁻). This results in a pH less than 7. Acidic solutions can form when a salt's cation comes from a weak base. For example, in the case of \(NH_4NO_3\), the cation \(NH_4^+\) is derived from a weak base, ammonium hydroxide (NH₄OH). This cation can donate a proton to the water, increasing the number of hydrogen ions. Thus, the solution becomes acidic:
\[NH_4^+ (aq) + H_2O (l) \rightarrow NH_3 (aq) + H_3O^+ (aq)\]
When analyzing salts for acidic properties, always check if the cation is capable of releasing protons.

Basic Solutions

A basic solution forms when the hydroxide ion (OH⁻) concentration dominates over hydrogen ions (H⁺). Basic solutions have a pH greater than 7. This can happen when a salt's anion comes from a weak acid. Consider \(RbOCl\), where the anion \(OCl^-\) originates from the weak acid hypochlorous acid (HOCl). In water, the \(OCl^-\) can accept a proton, resulting in an increased concentration of OH⁻ ions as follows:
\[OCl^- (aq) + H_2O (l) \rightleftharpoons HOCl (aq) + OH^- (aq)\]
It's important to evaluate whether the salt's anion is capable of accepting protons, as this determines basicity.

Neutral Solutions

Neutral solutions are characterized by an equal concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻), which give them a pH around 7. These solutions arise when both the cation and anion of a salt are derived from strong acids and bases, making them ineffective in altering water's ion balance. Consider \(NaCl\) and \(KI\)—both have neutral properties due to ions Na⁺, K⁺, Cl⁻, and I⁻, all resulting from strong acids and bases like NaOH and HCl. Therefore, they do not impact the solution's acidity or basicity, keeping it neutral with:
\[NaCl (aq) \rightleftharpoons Na^+ (aq) + Cl^- (aq)\]
and
\[KI (aq) \rightleftharpoons K^+ (aq) + I^- (aq)\]

Cations and Anions Analysis

To understand if a solution is acidic, basic, or neutral, it is crucial to analyze the behavior of its cations and anions.

• Neutral Cations/Anions: These typically come from strong acids or bases and don't affect the solution's pH significantly. Examples include \(Na^+\), \(Cl^-\), \(K^+\), and \(I^-\).
• Acidic Cations: Derived from weak bases, like \(NH_4^+\), can release protons and increase \(H^+\) concentration.
• Basic Anions: Originating from weak acids, like \(OCl^-\), can increase \(OH^-\) concentration by accepting protons.

Understanding these interactions helps predict solution behavior in terms of acidity or basicity.

Solution pH

The pH of a solution is a measure of its acidity or alkalinity. It is calculated by the concentration of hydrogen ions (H⁺), with the formula: \[\text{pH} = -\log_{10}[H^+]\] A pH less than 7 indicates an acidic solution, a pH of 7 represents a neutral solution, and a pH greater than 7 signifies a basic solution. The pH depends on the nature of the cations and anions in a salt. For example:

• An acidic solution has \(NH_4NO_3\), because \(NH_4^+\) increases H⁺ ions concentration.
• A basic solution involves salts like \(RbOCl\), where \(OCl^-\) increases OH⁻ ions.
• Neutral solutions like \(NaCl\) are balanced, with no effect from either ion type on water’s natural pH.

pH measurement aids in categorizing the nature of a solution, making it a fundamental aspect of chemical analysis.