Question

\(\mathrm{NH}_{3}(\mathrm{aq})\) conducts electric current only weakly. The same is true for acetic acid, \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(\mathrm{aq}) .\) When these solutions are mixed, however, the resulting solution conducts electric current very well. Propose an explanation.

Short answer

The mixture of ammonia and acetic acid solutions conducts electricity strongly due to the reaction between them which forms a salt, \(\mathrm{NH}_4 \mathrm{C}_2 \mathrm{H}_3 \mathrm{O}_2\). This salt is a strong electrolyte, ionizes completely in water, and thus improves the conductivity of the solution.

Step-by-step solution

Understand Weak Electrolytes

\(\mathrm{NH}_{3}(\mathrm{aq})\) and $\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(\mathrm{aq})$ are both weak electrolytes. Weak electrolytes ionize partially or not completely in water, meaning they produce a low concentration of ions which are able to move and carry a charge. Hence, the solutions of these compounds in water would only weakly conduct an electric current.

Explain the Acid-Base Reaction

When we mix \(\mathrm{NH}_3(aq)\) and \(\mathrm{HC}_2 \mathrm{H}_3 \mathrm{O}_2(aq)\), a chemical reaction takes place. This is an acid-base reaction, where \(\mathrm{NH}_3\) acts as a base and \(\mathrm{HC}_2 \mathrm{H}_3 \mathrm{O}_2\) acts as an acid. As a result, they react to form a salt, \(\mathrm{NH}_4 \mathrm{C}_2 \mathrm{H}_3 \mathrm{O}_2\), and water.

Resulting Conductivity

The salt, \(\mathrm{NH}_4 \mathrm{C}_2 \mathrm{H}_3 \mathrm{O}_2\) formed, is a strong electrolyte. It ionizes completely in water to give ions that can freely move and carry charge. Thus, the mixture of the solutions now conducts electricity much better than the individual solutions.

Key concepts

Weak Electrolytes

Weak electrolytes are substances that only partially dissociate into ions when dissolved in water. This means that only a small fraction of the solute exists as free ions in solution. Because of this limited ionization, weak electrolytes do not produce a high concentration of ions. Thus, they result in poor electrical conductivity.

Here are a few key features of weak electrolytes:

• They do not dissociate completely in solution.
• They include weak acids and weak bases.
• They exhibit low electrical conductivity in aqueous solutions due to fewer free-moving ions.

Examples include ammonia, \( ext{NH}_3\), and acetic acid, \( ext{HC}_2 ext{H}_3 ext{O}_2\), both of which ionize only slightly when in water. Hence, they produce an insufficient number of ions to conduct significant electric current. Mixing these weak electrolytes with other substances or under special conditions can sometimes lead to increased conductivity.

Acid-Base Reactions

An acid-base reaction is a chemical process where an acid reacts with a base to produce a salt and usually water. This type of reaction is fundamental in chemistry, involving the transfer of protons between the reacting species.

For instance, when ammonia (\( ext{NH}_3\)) and acetic acid (\( ext{HC}_2 ext{H}_3 ext{O}_2\)) are mixed, a reaction occurs:

• Ammonia acts as a base and accepts a proton.
• Acetic acid, being the acid, donates a proton.
• The reaction products are a salt, \( ext{NH}_4 ext{C}_2 ext{H}_3 ext{O}_2\), and water.

This salt formation increases the ionic content in the solution, leading to improved electrical conductivity. Such reactions are integral in transforming weakly conducting solutions into highly conductive ones.

Electrical Conductivity of Solutions

Electrical conductivity in solutions refers to the ability of a solution to conduct an electric current. This property is largely determined by the presence and mobility of ions within the solution. The more ions present, and the more freely they can move, the better the conductivity.

Key points about electrical conductivity:

• It depends on the concentration and type of ions present.
• Solutions of strong electrolytes have high conductivity due to complete ionization.
• Weak electrolytes have low conductivity as they ionize only partially.

When ammonia and acetic acid react to form the salt \( ext{NH}_4 ext{C}_2 ext{H}_3 ext{O}_2\), the number of free ions in the solution increases significantly. The newly formed salt is a strong electrolyte which contributes to the enhanced conductivity, making it a better conductor of electricity compared to the original solutions.

Ionization in Water

Ionization is the process in which a molecule splits into ions when dissolved in water. It is an essential process for generating ions that are capable of conducting electricity. The degree to which substances ionize can range from complete to very little, influencing the substance's classification as strong or weak electrolytes.

Here's how it works:

• Strong electrolytes: These ionize completely, resulting in high concentrations of ions. Examples include salts like sodium chloride.
• Weak electrolytes: These ionize partially, leading to reduced ion concentrations and thus limited electrical conductivity.
• Ionization is crucial in determining a solution's conductivity.

When ammonia and acetic acid are both dissolved in water, their low degree of ionization results in poor conductivity. However, upon reacting and forming a more ionized compound, \( ext{NH}_4 ext{C}_2 ext{H}_3 ext{O}_2\), conductivity increases due to the formation of more ions.