Problem 42 - Chemistry: An Atoms-Focused Approach

Question

What is the molarity of each ion in a \(0.035 M\) aqueous solution of (a) \(\mathrm{NH}_{4} \mathrm{Cl} ;\) (b) \(\mathrm{Li}_{2} \mathrm{SO}_{4} ;\) (c) \(\mathrm{MgBr}_{2} ?\)

Step-by-Step Solution

Answer

Answer: The molarity of each ion (NH4+ and Cl-) in the 0.035 M NH4Cl aqueous solution is 0.035 M.

Step 1: (a) Solution of NH4Cl#aquarium_synthetic_exercise#

NH4Cl is a soluble ionic compound that, when dissolved in water, dissociates into ammonium ions (NH4+) and chloride ions (Cl-).Thus, we may write the dissolving reaction: NH4Cl(s) --> NH4+(aq) + Cl-(aq) For every mole of NH4Cl that dissolves, one mole of NH4+ and one mole of Cl- are produced. Since we are given a 0.035 M solution of NH4Cl, we can directly relate this to the concentration of each ion: [NH4+] = [Cl-] = 0.035 M So, the molarity of each ion (NH4+ and Cl-) in the NH4Cl aqueous solution is 0.035 M.

Key Concepts

Ionic Compounds

Ionic compounds are substances made up of positively charged ions and negatively charged ions. These ions are held together by strong electrostatic forces in a structure known as an ionic lattice. For example, in ammonium chloride (\(\mathrm{NH}_{4} \mathrm{Cl} \)), the ammonium ion (\(\mathrm{NH}_{4}^{+} \)) and the chloride ion (\(\mathrm{Cl}^{-} \)) form an ionic bond.
The formation of ionic compounds involves the transfer of electrons between atoms, leading to the formation of ions.

Important characteristics of ionic compounds include:

• High melting and boiling points due to strong interactions.
• Ability to dissolve in water, creating an aqueous solution.
• Conductivity in molten form or when dissolved in water.

Understanding these properties is essential for exploring how these compounds behave in different environments, such as in aqueous solutions.

Aqueous Solutions

An aqueous solution is a solution where water acts as the solvent. When ionic compounds dissolve in water, they form an aqueous solution. Water, being a polar solvent, is excellent at dissolving ionic compounds due to its ability to stabilize ions.

Aqueous solutions are crucial in chemistry for various reasons:

• Facilitate reactions that do not occur in the solid state.
• Enable easy measurement and calculation of concentrations, like molarity.
• Support the dissociation of ionic compounds into their respective ions.

Not only do they allow for these chemical processes, but they also make it possible to study the interactions between ions and molecules in a liquid medium.

Dissociation in Water

Dissociation is the process where ionic compounds separate into ions when dissolved in water. This is a key aspect of understanding how substances behave in aqueous solutions. For instance, when \(\mathrm{NH}_{4} \mathrm{Cl} \) dissolves, it breaks apart into \(\mathrm{NH}_{4}^{+} \) and \(\mathrm{Cl}^{-} \).

The process of dissociation entails:

• Ions interacting with water molecules, which stabilize them and keep them apart.
• Formation of hydrated ions, where water molecules surround and isolate each ion.
• The balance of charges, ensured by the solvent's polarity, maintaining electrical neutrality.

This process is fundamental for reactions in solutions, affecting pH, conductivity, and overall chemical behavior.