Problem 87 - Chemistry: An Atoms-Focused Approach

Question

Consider the following compounds: \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) \(\mathrm{CH}_{3} \mathrm{COOH}, \mathrm{Ca}(\mathrm{OH})_{2},\) and \(\mathrm{HClO}_{4}\) a. Identify the Arrhenius acid(s). b. Identify the Arrhenius base(s). c. Identify the Bronsted-Lowry acid(s). d. Identify the Brensted-Lowry base(s).

Step-by-Step Solution

Answer

Based on the given compounds, the Arrhenius acids are CH₃COOH and HClO₄, the Arrhenius base is Ca(OH)₂, the Bronsted-Lowry acids are CH₃COOH and HClO₄, and the Bronsted-Lowry bases are CH₃NH₂ and Ca(OH)₂.

Step 1: (Step 1: Identify Arrhenius acids and bases)

To identify the Arrhenius acids and bases among the given compounds, we must look at the compounds which, when dissolved in water, will release H+ ions or OH- ions.Positive ions are produced in the form of H3O+ hydronium ions. Negative hydroxide ions are produced in the OH- form. The given compounds are: 1. \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) 2. \(\mathrm{CH}_{3} \mathrm{COOH}\) 3. \(\mathrm{Ca}(\mathrm{OH})_{2}\) 4. \(\mathrm{HClO}_{4}\) a. Arrhenius acids: The compounds which produce H+ ions when dissolved in water. In this case, the compounds are: 2. \(\mathrm{CH}_{3} \mathrm{COOH}\) 4. \(\mathrm{HClO}_{4}\) b. Arrhenius bases: The compounds which produce OH- ions when dissolved in water. In this case, the compound is: 3. \(\mathrm{Ca}(\mathrm{OH})_{2}\)

Step 2: (Step 2: Identify Bronsted-Lowry acids and bases)

To identify the Bronsted-Lowry acids and bases, we must look at the compounds which can donate H+ ions (Proton donors) or accept H+ ions (Proton acceptors). c. Bronsted-Lowry acids: Proton donors (can donate an H+ ion). In this case, the compounds are: 2. \(\mathrm{CH}_{3} \mathrm{COOH}\) 4. \(\mathrm{HClO}_{4}\) d. Bronsted-Lowry bases: Proton acceptors (can accept an H+ ion). In this case, the compounds are: 1. \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) 3. \(\mathrm{Ca}(\mathrm{OH})_{2}\) (In this compound, the OH- ions can accept H+ ions) In summary: a. Arrhenius acids: \(\mathrm{CH}_{3} \mathrm{COOH}\), \(\mathrm{HClO}_{4}\) b. Arrhenius bases: \(\mathrm{Ca}(\mathrm{OH})_{2}\) c. Bronsted-Lowry acids: \(\mathrm{CH}_{3} \mathrm{COOH}\), \(\mathrm{HClO}_{4}\) d. Bronsted-Lowry bases: \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) , \(\mathrm{Ca}(\mathrm{OH})_{2}\)

Key Concepts

Arrhenius Acids and Bases

The Arrhenius theory of acids and bases is one of the simplest and earliest theories proposed. According to Arrhenius, an acid is a substance that increases the concentration of \(\text{H}^+\) ions, or more precisely hydronium ions (\(\text{H}_3\text{O}^+\)), in an aqueous solution. Arrhenius bases, on the other hand, are substances that increase the concentration of hydroxide ions (\(\text{OH}^-\)) in water. This theory is specific to aqueous solutions and is primarily concerned with the ions produced in these solutions.

In the original exercise, we identified two Arrhenius acids: \(\text{CH}_3\text{COOH}\) (acetic acid) and \(\text{HClO}_4\) (perchloric acid). These compounds release \(\text{H}^+\) ions when dissolved in water:

• \(\text{CH}_3\text{COOH (aq)} \rightarrow \text{CH}_3\text{COO}^- + \text{H}_3\text{O}^+\)
• \(\text{HClO}_4\text{ (aq)} \rightarrow \text{ClO}_4^- + \text{H}_3\text{O}^+\)

For the Arrhenius base, we identified \(\text{Ca(OH)}_2\) (calcium hydroxide), which dissociates in water to produce hydroxide ions:

• \(\text{Ca(OH)}_2 \rightarrow \text{Ca}^{2+} + 2\text{OH}^-\)

The differences in how these substances dissociate are pivotal in differentiating between Arrhenius acids and bases.

Bronsted-Lowry Theory

The Bronsted-Lowry theory takes a broader view compared to Arrhenius's. According to this theory, acids are proton donors, meaning they can give away \(\text{H}^+\) ions, whereas bases are proton acceptors, which are capable of accepting \(\text{H}^+\) ions. This theory is not limited to aqueous solutions and can apply to reactions in gaseous or non-aqueous solutions as well.

In the given exercise, the Bronsted-Lowry acids identified were the same as the Arrhenius acids: \(\text{CH}_3\text{COOH}\) and \(\text{HClO}_4\). Both of these compounds can donate protons in a chemical reaction:

• \(\text{CH}_3\text{COOH} + \text{H}_2\text{O} \rightarrow \text{CH}_3\text{COO}^- + \text{H}_3\text{O}^+\)

Bronsted-Lowry bases from the exercise include \(\text{CH}_3\text{NH}_2\) (methylamine) and \(\text{Ca(OH)}_2\). Methylamine can accept a proton, forming \(\text{CH}_3\text{NH}_3^+\):

• \(\text{CH}_3\text{NH}_2 + \text{H}^+ \rightarrow \text{CH}_3\text{NH}_3^+\)

Understanding proton donation and acceptance helps in identifying acids and bases that might not be evident through the Arrhenius definition.

Proton Transfer Reactions

Proton transfer reactions are fundamental processes in chemistry where a proton (\(\text{H}^+\) ion) is transferred from one molecule (the acid) to another (the base). This is an essential part of the Bronsted-Lowry theory, illustrating the concept of conjugate acids and bases.

When an acid donates a proton, it forms a conjugate base, while a base accepting a proton forms a conjugate acid. For example, \(\text{CH}_3\text{COOH}\) donates a proton to \(\text{CH}_3\text{COO}^-\), its conjugate base.

• The conjugate acid-base pair for \(\text{CH}_3\text{COOH}\) and \(\text{CH}_3\text{COO}^-\) demonstrates this process.
• Similarly, when methylamine ( ext{CH}_3 ext{NH}_2) accepts a proton, it becomes \(\text{CH}_3\text{NH}_3^+\), forming a conjugate acid-base pair.

This understanding of proton transfer is crucial for recognizing how substances interact and change in different chemical environments. It helps visualize the flow of protons in a chemical system, highlighting the dynamic nature of acids and bases.