Question

When 1 mole of gaseous hydrogen chloride is dissolved in enough water to make \(1 \mathrm{~L}\) of solution, approximately how many \(\mathrm{HCl}\) molecules remain in the solution? Explain.

Short answer

When 1 mole of gaseous hydrogen chloride is dissolved in 1 L of water, it dissociates completely into its individual ions (\(\mathrm{H^+}\) and \(\mathrm{Cl^-}\)): \( \mathrm{HCl {(g)}}\rightarrow \mathrm{H^+ {(aq)}} + \mathrm{Cl^- {(aq)}}\) Since virtually all \(1 \mathrm{~mol}\) or \(6.022 \times 10^{23}\) HCl molecules have ionized in the solution, it is reasonable to assume that there are almost no HCl molecules remaining. Therefore, approximately 0 HCl molecules remain in the solution.

Step-by-step solution

Calculate the number of HCl molecules in 1 mole

One mole of any substance contains Avogadro's number of particles, which is 6.022 × 10^23. Thus, 1 mole of HCl gas has 6.022 × 10^23 HCl molecules.

Determine the number of HCl molecules that would remain in the solution

When HCl is dissolved in water, it ionizes to form H+ and Cl- ions, as shown in this reaction: \( \mathrm{HCl {(g)}}\rightarrow \mathrm{H^+ {(aq)}} + \mathrm{Cl^- {(aq)}}\) Since each HCl molecule dissociates completely into its individual ions when dissolved in water, we can assume that virtually all HCl molecules have ionized in the solution. Therefore, it is reasonable to assume that there are almost no HCl molecules remaining in the solution. So the answer would be approximately 0 HCl molecules remain in the solution.

Key concepts

Avogadro's Number

When it comes to understanding chemical quantities in labs and real-world applications, Avogadro's number is a cornerstone concept in chemistry. Representing a constant at 6.022 × 10^23, it specifies exactly how many atoms, molecules, or ions are in one mole of a substance. This intriguing number isn’t random; it was chosen because it reflects the number of carbon atoms in exactly 12 grams of pure carbon-12 (the isotope of carbon).

Let's put this into perspective: if we consider a mole of hydrogen chloride gas, as in our original exercise, it should have 6.022 × 10^23 molecules. It's akin to saying a dozen eggs contains 12 eggs. Here, 'a dozen' is ‘Avogadro’s number,’ and ‘eggs’ are the tiny particles making up the substance. This number is pivotal in converting microscopic chemical quantities into macroscopic amounts we can work with, such as the number of molecules in a sample.

Ionic Dissociation

Ionic dissociation is a concept that explains how compounds split into ions when dissolved in solvents like water. When ionic compounds dissolve, the individual ions break apart and become surrounded by solvent molecules, in a process that usually involves the attraction of solvent molecules to the ions, which stabilizes them in solution.

For ionic compounds like common salt, table salt, or our example of hydrogen chloride in gaseous form, dissolving them in water results in complete dissociation into sodium (Na+) and chloride (Cl-) ions for salt, and hydrogen (H+) and chloride (Cl-) ions for HCl. In ideal situations, we assume that each unit of the compound separates into its component ions, though in practice, the extent of dissociation may vary based on various factors such as concentration, temperature, and the nature of the solvent.

Hydrogen Chloride Ionization

Hydrogen chloride ionization specifically refers to the process HCl undergoes when it dissolves in water. Typically, gaseous HCl is made up of neutral molecules. However, when added to water, it demonstrates strong acidity by almost completely dissociating into hydrogen cations (H+) and chloride anions (Cl-). This transformation from a neutral molecule to ions is known as ionization.

This process is highly efficient for strong acids like HCl, resulting in nearly all molecules turning into ions in solution. That is why, in our exercise, we inferred that there are almost no HCl molecules left following dissolution and ionization in water. This ionization is a key part of understanding how acids behave in aqueous solutions, and it is a fundamental principle in the study of acid-base reactions, electrochemistry, and many other areas of chemistry.