Question

Household ammonia, used as a window cleaner and for other cleaning purposes, is \(\mathrm{NH}_{3}(\mathrm{aq}) .\) The \(\mathrm{NH}_{3}\) present in a 5.00 \(\mathrm{mL}\) sample is neutralized by 28.72 \(\mathrm{mL}\) of \(1.021 \mathrm{M} \mathrm{HCl}\). The net ionic equation for the neutralization is \(\mathrm{NH}_{3}(\mathrm{aq})+\mathrm{H}^{+}(\mathrm{aq}) \longrightarrow \mathrm{NH}_{4}^{+}(\mathrm{aq})\) What is the molarity of \(\mathrm{NH}_{3}\) in the sample?

Short answer

The molarity of the \(NH_3\) in the sample is 5.86 M.

Step-by-step solution

Understand the reaction

The given ionic equation represents the reaction between ammonia and hydrochloric acid. In the reaction, one molecule of ammonia reacts with one hydrogen ion to form an ammonium ion. As the stoichiometric coefficient of both reactants is 1, they react in a 1:1 ratio.

Determine the number of moles of \(HCl\)

To find the molarity of the \(NH_3\), we first need to determine the number of moles of \(HCl\) used in the reaction. We can use the formula for molarity (M) which is M = n/V, where n is the number of moles and V is the volume in liters. Rearranging the formula, we get n = M * V. Substituting given values, we have n = 1.021 mol/L * 0.02872 L = 0.02932 mol.

Determine the molarity of \(NH_3\)

As \(NH_3\) and \(H^+\) react in a 1:1 ratio, the number of moles of \(NH_3\) is the same as \(HCl\), which we calculated in the previous step. Now we can calculate the molarity of \(NH_3\) using the same formula for molarity (M = n/V), but now using the volume of the \(NH_3\) solution. So, M = 0.02932 mol / 0.005 L = 5.86 M. Therefore, the molarity of the \(NH_3\) in the sample is 5.86 M.

Key concepts

Neutralization Reaction

In chemistry, a neutralization reaction is a chemical reaction wherein an acid and a base react to form water and a salt. This specific type of reaction often involves the transfer of protons, typically from the acid to the base. Neutralization is a key concept in acid-base chemistry and plays a vital role in various scientific and industrial processes.
Neutralization can be seen when hydrochloric acid (HCl) and ammonia (NH₃) interact. In this case, the reaction simplifies to the transfer of hydrogen ions (H⁺) from the acid to the base, resulting in the formation of ammonium ions (NH₄⁺). Such reactions help us understand how different substances combine, and they are essential in calculations like determining the molarity of a solution.
In practice, neutralization reactions can be used to calculate unknown concentrations. By measuring the substance required to neutralize a solution, chemists determine how much acid or base is present in a sample. This is incredibly effective and widely used in various laboratory settings.

Ionic Equation

Ionic equations depict the actual species involved in a chemical reaction, particularly in aqueous solutions. Unlike a molecular equation that lists compounds as neutral molecules, an ionic equation shows ions separately. This provides a clearer picture of the chemical processes occurring in solution.
The ionic equation for the neutralization between NH₃(aq) and H⁺(aq) is:

• NH₃(aq) + H⁺(aq) → NH₄⁺(aq)

This equation illustrates the transfer of protons from a hydrogen ion to ammonia, forming an ammonium ion.
By breaking down the involved species, ionic equations help chemists detect which ions participate in a reaction and which are only spectators. They provide vital insights into reaction mechanics and stoichiometry.

Stoichiometry

Stoichiometry is the aspect of chemistry that involves calculating the relative quantities of reactants and products in chemical reactions. It uses the balanced equation for the reaction and includes concepts like mole ratios, balancing equations, and conversion of units.
In the exercise at hand, stoichiometry was applied to determine how many moles of ammonia reacted. Given that ammonia and hydrogen ions react in a 1:1 molar ratio, if you know the moles of one component (like HCl), you know the amount of the other (NH₃ without any complex calculations).
Useful for understanding reaction yields and limiting reagents, stoichiometry allows chemists to predict how much of one substance will react with a given amount of another substance. It's essential in both theoretical studies and practical applications, enabling precise formulation and prediction of chemical outcomes.

Acid-Base Chemistry

Acid-base chemistry focuses on the reactions and properties of acids and bases. These are fundamental classes of compounds that engage in proton (H⁺) transfer reactions. In daily life, acid-base reactions are crucial in fields like agriculture, medicine, and cleaning products.
Ammonia is a weak base, and hydrochloric acid is a strong acid. When they react, the acid donates a proton to the base, forming water and salt. This classic example reflects the behavior of acids (proton donors) and bases (proton acceptors) defined by the Brønsted-Lowry theory.

• Ammonia acting as a base accepts protons, becoming ammonium.
• HCl provides protons and exists as chloride ions after donating the proton.

Understanding acid-base interactions help predict actions in solutions, manage wastewater, develop medicines, and even manufacture soaps and detergents. Given their significance, grasping acid-base chemistry fundamentals enriches one's comprehension of not only chemical processes but also myriad practical applications.