Problem 109 - General Chemistry: Principles and Modern Applications

Question

The reaction of \(\mathrm{CH}_{3} \mathrm{COOH}(\) aq) proceeds furthest toward completion with a base when that base is (a) \(\mathrm{H}_{2} \mathrm{O} ;\) (b) \(\mathrm{CH}_{3} \mathrm{NH}_{3}^{+} ;\) (c) \(\mathrm{NH}_{4}^{+} ;\) (d) \(\mathrm{Cl}^{-} ;\) (e) \(\mathrm{CO}_{3}^{2-}\).

Step-by-Step Solution

Answer

The base that will make the reaction of \(\mathrm{CH}_{3} \mathrm{COOH}\) proceed furthest toward completion is \(\mathrm{CO}_{3}^{2-}\).

Step 1: Analyze the Bases

We have five substances that can act as bases. Water (\(\mathrm{H}_{2} \mathrm{O}\)) is a weak base, \(\mathrm{CH}_{3} \mathrm{NH}_{3}^{+}\) and \(\mathrm{NH}_{4}^{+}\) are weak because of their positively charged ammonium group. Chloride ions (\(\mathrm{Cl}^{-}\)) can act as bases but are extremely weak due to their complete electronic shell. The carbonate ion (\(\mathrm{CO}_{3}^{2-}\)) is a moderate-strong base due its extra lone pairs.

Step 2: Reaction capabilities

Now that we have analyzed the bases, we understand that moderate to strong bases can make the reaction proceed further. \(\mathrm{NH}_{4}^{+}\), \(\mathrm{Cl}^{-}\) and \(\mathrm{CH}_{3} \mathrm{NH}_{3}^{+}\) cannot accept protons effectively due to their positive charge or complete electronic shell, so they will be less efficient in reacting with the acid.

Step 3: Determine the most effective base

Given that \(\mathrm{CO}_{3}^{2-}\) is the only moderate-strong base (and thus more capable of reacting with the acid than the others) in this list, we can say that it will react most effectively, making the reaction proceed furthest.

Key Concepts

Acetic Acid

Acetic acid is a weak acid that is commonly found in household vinegar. Its chemical formula is \( ext{CH}_3 ext{COOH}\). As a weak acid, it doesn't completely dissociate into its ions in water. Instead, it partially ionizes, rendering it a reliable case to explore acid-base reactions.

Understanding acetic acid involves knowing that it can donate a hydrogen ion (proton) during a reaction. This capability defines its acidity. When it ionizes, acetic acid forms acetate ions \( ext{CH}_3 ext{COO}^-\) and hydrogen ions \( ext{H}^+\).

• Formula: \( ext{CH}_3 ext{COOH}\)
• Ionizes to: \( ext{CH}_3 ext{COO}^-\) and \( ext{H}^+\)
• Found in: Vinegar

The strength of an acid, like acetic acid, is measured by its ability to donate this hydrogen ion when it encounters a base in a solution.

Carbonate Ion

The carbonate ion, \( ext{CO}_3^{2-}\), is a polyatomic ion that plays a critical role in acid-base reactions. It carries two negative charges. These charges make it a strong candidate for accepting protons, facilitating the forward movement of reactions involving acids.

In the context of reacting with acids like acetic acid, the carbonate ion acts as a base because it can accept protons and react, forming bicarbonate or carbonic acid depending on the environment. This reaction illustrates its strong base qualities compared to weaker bases.

• Formula: \( ext{CO}_3^{2-}\)
• Charge: -2
• Role: Proton acceptor in reactions

The efficient reactivity of the carbonate ion makes it an effective participant in driving reactions towards completion, outmatching weaker bases such as chloride ions or ammonium.

Base Strength

Understanding the strength of a base is central to predicting the outcome of an acid-base reaction. Base strength refers to a base's ability to accept protons. Some common features indicating stronger base strength include the presence of lone electron pairs and negative charges.

The five bases analyzed in the exercise have varying strengths:

• Water (\( ext{H}_2 ext{O}\)): A weak base due to its neutral nature.
• Ammonium ions (\( ext{CH}_3 ext{NH}_3^+\) and \( ext{NH}_4^+\)): Generally weak because they are more inclined to part with a hydrogen ion than acquire one.
• Chloride ion (\( ext{Cl}^-\)): An extremely weak base since its filled electronic shell prevents effective proton acceptance.
• Carbonate ion (\( ext{CO}_3^{2-}\)): A moderate-strong base due to its considerable negative charge and the ability to accept protons efficiently.

Among these, the carbonate ion stands out as the most robust base, capable of inducing significant progression in an acid-base reaction.

Completion Reaction

Completion reactions in the context of acid-base chemistry refer to reactions that proceed to completion, meaning they continue until one of the reactants is entirely consumed. One key factor driving such reactions to completion is the relative strength of the bases or acids involved.

If an acid like acetic acid encounters a base strong enough (like the carbonate ion), the reaction is more likely to proceed to completion. The strong base effectively accepts protons, resulting in the formation of products that inhibit the reverse reaction.

This concept is crucial because it helps predict which acid-base reactions are more efficient and practically significant. A strong base, such as the carbonate ion, ensures that more of the acid is neutralized completely, enhancing the reaction's overall efficiency.

• Completion usually involves a strong base or acid.
• Products are formed that are stable and unlikely to revert to reactants.
• Essential for effective titrations in laboratory settings.

This understanding helps in various applications, from chemical manufacturing to laboratory analyses, showcasing the importance of recognizing which reactions are completion prone.