Problem 14 - Chemistry The Science in Context

Question

When \(\operatorname{Cr}\left(\mathrm{NO}_{3}\right)_{3}\) dissolves in water, which of the following species are nearest the \(\mathrm{Cr}^{3+}\) ions? a. Other \(\mathrm{Cr}^{3+}\) ions b. \(\mathrm{NO}_{3}^{-}\) ions c. \(\mathrm{H}_{2} \mathrm{O}\) molecules with the \(\mathrm{O}\) atoms closest to the \(\mathrm{Cr}^{3+}\) d. \(\mathrm{H}_{2} \mathrm{O}\) molecules with the \(\mathrm{H}\) atoms closest to the \(\mathrm{Cr}^{3+}\)

Step-by-Step Solution

Answer

Answer: NO3^- ions are nearest to the Cr^3+ ions.

Step 1: Write down the dissociation of Cr(NO3)3 in water

When dissociating in water, Cr(NO3)3 dissociates into Cr^3+ ions and NO3^- ions: Cr(NO3)3 (aq) -> Cr^3+ (aq) + 3 NO3^- (aq)

Step 2: Analyze the possible interactions with Cr^3+ ions

The possible interactions between Cr^3+ ions and other species include: a. Other Cr^3+ ions. b. NO3^- ions. c. H2O molecules with the oxygen atoms closest to the Cr^3+ ions. d. H2O molecules with the hydrogen atoms closest to the Cr^3+ ions.

Step 3: Determine the species with the strongest electrostatic interaction

The electrostatic interaction is mainly determined by the charges of the interacting species. The higher the charges and the closer the distance, the stronger the interaction. a. Other Cr^3+ ions are also positively charged, so they will repel each other and not be nearest to the Cr^3+ ions. b. NO3^- ions are negatively charged, which can interact strongly with the positively charged Cr^3+ ions due to their opposite charges. c. In H2O molecules, oxygen atoms have a partial negative charge, and hydrogen atoms have a partial positive charge. Oxygen atoms being partially negative can interact with Cr^3+ ions. d. Hydrogen atoms in H2O molecules have a partial positive charge, which will not interact strongly with Cr^3+ ions because they are both positively charged, resulting in electrostatic repulsion.

Step 4: Compare the interactions and select the nearest species

Comparing all the types of interactions, we find that the interaction between the Cr^3+ ions and the NO3^- ions (option b) is the strongest due to their opposite charges. The interaction between Cr^3+ and oxygen atoms in H2O molecules (option c) is also significant. However, the strength of interaction between an ion and an ion (option b) is stronger than the interaction between an ion and a polar molecule (option c). So, the species nearest to the Cr^3+ ions are: b. NO3^- ions.

Key Concepts

Electrostatic Interaction

When studying chemistry, electrostatic interaction is a vital concept to understand. It involves the force between charged particles. This interaction is the result of electric charges attracting or repelling each other.

• If two particles have opposite charges, they attract; if they have the same charge, they repel.
• The strength of this interaction depends on both the magnitude of the charge and the distance between the charges.

In the case of chromium nitrate (\[\operatorname{Cr}(\mathrm{NO}_3)_3\]), when it dissolves in water, electrostatic interaction comes into play between the ions formed. The dissociation results in \[\mathrm{Cr}^{3+}\] and \[\mathrm{NO}_3^{-}\] ions, which are attracted to each other due to their opposing charges.These interactions are critical because they affect how substances like chromium nitrate behave once dissolved, especially with the ions spreading throughout the solvent. Electrostatic interaction helps maintain the structure and stability of the dissolved particles in the solution.

Dissolution in Water

Water is often referred to as the 'universal solvent' for its ability to dissolve many substances. The process of dissolution involves breaking down a compound into its individual ions or molecules. In the case of chromium nitrate (\[\operatorname{Cr}(\mathrm{NO}_3)_3\]), it undergoes dissolution as it interacts with water.During this process, water molecules surround the individual \[\mathrm{Cr}^{3+}\] and \[\mathrm{NO}_3^{-}\] ions. The attractive forces between the water molecules and these ions help pull the ionic lattice apart. This results in the compound dispersing into its constituent ions within the solution.

• The dielectric nature of water, due to its high polarity, plays a critical role in neutralizing the charged ions.
• The dissolution process also allows for the ions to move freely, which is important for the potential reactivity and chemical interactions.

Understanding dissolution is essential for many chemical processes and reactions, making water an indispensable component in chemical solutions.

Ion-Dipole Interaction

The concept of ion-dipole interaction is key to understanding how ions behave in a polar solvent like water. When chromium nitrate dissolution occurs, the ions form specific interactions with water molecules. Water, being polar, means its molecules have a partial positive and negative charge due to the uneven distribution of electrons:

• The oxygen atom in water has a partial negative charge.
• The hydrogen atoms in water have a partial positive charge.

For the \[\mathrm{Cr}^{3+}\] ions, these ion-dipole interactions are mainly between the positive ions and the negative dipole of water's oxygen. This interaction is pivotal as it stabilizes the ions in solution.On the other hand, \[\mathrm{NO}_3^{-}\] ions primarily interact with the positive end of the water dipole - the hydrogen atoms. This alignment helps in keeping the ions dispersed and preventing them from reassociating, thereby ensuring a homogeneous solution.Ion-dipole interactions are incredibly important in chemistry because they help maintain the solubility and stability of ions in solutions, enabling a broad range of reactions and processes.