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The reaction of ammonia with water is an important chemical process that highlights ammonia's basic properties. Ammonia, represented by the chemical formula \( \text{NH}_3 \), interacts with water molecules leading to a reversible reaction. This means the reaction can proceed in both directions. When ammonia (\(\text{NH}_3\)) reacts with water (\(\text{H}_2\text{O}\)), it acts as a base.

• Ammonia accepts a proton (\(\text{H}^+\)) from a water molecule.
• This process produces ammonium ions (\(\text{NH}_4^+\)) and hydroxide ions (\(\text{OH}^-\)).

The balanced chemical equation for this process:\[\text{NH}_3 (aq) + \text{H}_2\text{O} (l) \rightleftharpoons \text{NH}_4^+ (aq) + \text{OH}^- (aq)\]This equation highlights the role of ammonia as a proton acceptor, demonstrating its basic nature. This reaction is key in determining the alkalinity of the solution, which is how basic it is, and it forms the basis for the pH calculation.

In the ammonia and water reaction, chemical equilibrium plays a crucial role. Chemical equilibrium occurs when the forward and reverse reaction rates are equal, meaning no net change in concentration of reactants and products. This state is dynamic, constantly shifting between the reactants and products to maintain balance.
The concept of equilibrium is significant because:

• The concentrations of ammonia, water, ammonium, and hydroxide ions stabilize over time.
• The equilibrium position depends on the extent of the reaction and the conditions such as temperature and concentration.

In our example problem, it's stated that 0.42% of ammonia reacts, showing that most ammonia does not significantly convert into products. Measuring this small change is detectable through parameters like electrical conductivity, as the formation of ions influences how well the solution conducts electricity.

Electrical conductivity in a solution indicates the solution’s ability to conduct electricity through the presence of ions. The more ions in the solution, the better its conductivity. In the context of the ammonia reaction, the formation of \(\text{NH}_4^+\) and \(\text{OH}^-\) ions increases the conductivity of the solution, as these ions are charge carriers.
Here's why this is important:

• Conductivity measurements can help calculate how much ammonia reacts with water.
• By knowing the percentage of ammonia that forms ions, we can understand the solution's ion concentration more deeply.

The measured \(0.42\%\) conversion of ammonia to ions demonstrates a measurable change in electrical properties, which aids in calculating the pH via the concentration of hydroxide ions.

Understanding molarity and moles conversion is key to solving the exercise. Molarity is the concentration of a solution expressed as the number of moles of solute per liter of solution. To find molarity, you need to convert grams of a substance to moles using the molar mass and then divide by the volume in liters.
Here’s how it works in practice:

• Start with the mass of ammonia, \(4.25 \text{ g}\), and convert it to moles using its molar mass \(17.03 \text{ g/mol}\).
• Calculate the total moles: \[\text{moles of } \text{NH}_3 = \frac{4.25 \text{ g}}{17.03 \text{ g/mol}} \approx 0.25 \text{ mol} \]
• Determine the moles that reacted by accounting for the \(0.42\%\) conversion: \[ \text{moles of reacted } \text{NH}_3 = 0.25 \text{ mol} \times 0.0042 \approx 0.00105 \text{ mol}\]
• Finally, calculate the concentration of ions in the solution by dividing moles by volume in liters.

This conversion and calculation process is essential for analyzing chemical reactions in a quantitative manner and supports the accurate determination of pH.