Question

Differentiate between what happens when the following are added to water a. polar solute versus nonpolar solute b. KF versus \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\) c. RbCl versus AgCl d. \(\mathrm{HNO}_{3}\) versus \(\mathrm{CO}\)

Short answer

When added to water: a) Polar solutes dissolve due to hydrogen bonds or electrostatic interactions, while nonpolar solutes don't dissolve or dissolve poorly. b) Both KF (ionic) and C6H12O6 (polar) are soluble, but KF dissociates into ions, whereas C6H12O6 stays as individual molecules. c) RbCl (ionic) dissolves into ions, while AgCl has low solubility due to its lattice structure. d) HNO3 makes the solution acidic by ionizing, while CO has little effect as it is nonpolar and does not interact strongly with water.

Step-by-step solution

a. Polar vs Nonpolar solute

Polar solutes have a charged or polar functional group, which allows them to form hydrogen bonds or electrostatic interactions with water molecules. This results in them being soluble in water. On the other hand, nonpolar solutes do not have polar functional groups, so they do not form strong interactions with water. This often makes them insoluble or less soluble in water.

b. KF vs. C6H12O6

KF is potassium fluoride, an ionic compound, which will dissociate into potassium (K+) and fluoride (F-) ions when added to water. These ions will then become hydrated by the water molecules, leading to a homogeneous solution. C6H12O6 is glucose, a polar molecule with multiple hydroxyl (OH) groups that can form hydrogen bonds with water, making it soluble. Both KF and C6H12O6 are soluble in water, but KF dissociates into ions while C6H12O6 remains as individual molecules.

c. RbCl vs. AgCl

RbCl is rubidium chloride, an ionic compound that will dissolve in water by breaking down into its constituent ions, Rb+ and Cl-. Similar to KF, these ions will then become hydrated by water molecules, resulting in a homogeneous solution. Conversely, AgCl (silver chloride) has low solubility in water due to its strong ionic lattice structure, which is not easily broken down by the hydration energy of the water molecules. AgCl will only marginally dissolve in water, producing a saturated solution with undissolved solid AgCl present.

d. HNO3 vs. CO

HNO3 is nitric acid, a polar, soluble compound in water. When it dissolves, it ionizes to produce H+ and NO3- ions, making the resulting solution acidic. Carbon monoxide (CO) is a nonpolar, covalent compound, which has weak solubility in water due to the lack of strong interactions between carbon monoxide and water molecules. Since CO does not dissociate into ions or interact strongly with water, it does not affect the pH of the water. In summary, adding HNO3 makes the solution acidic, while CO has little effect on the water properties.

Key concepts

Polar and nonpolar solutes

In the world of chemistry, understanding the nature of solutes is crucial for predicting their behavior in various solvents. Solutes can be categorized into polar and nonpolar based on their affinity to water, a polar solvent.
Polar solutes have molecules with polar bonds and an uneven charge distribution, enabling them to form hydrogen bonds or electrostatic attractions with water. These interactions make polar solutes highly soluble in water. For instance, table salt (NaCl) is polar and dissolves readily due to its ability to dissociate into ions that interact skillfully with water.
In contrast, nonpolar solutes lack charge or have an even distribution of electrons. This causes them to have minimal interactions with water, leading to poor solubility. Oil is a classic example, often seen separating on water surfaces because its molecules do not attract water molecules. Understanding these differences is essential for areas such as drug delivery and environmental science.

Ionic and molecular compounds

Ionic and molecular compounds behave differently in solvents like water due to their distinct structures and bonding.
Ionic compounds, like potassium fluoride (KF), consist of positive and negative ions. When added to water, these compounds disassociate into free ions due to the polar nature of water, which stabilizes ions through hydration. This process allows ionic compounds to dissolve efficiently, creating electrolytic solutions.On the other hand, molecular compounds, like glucose ( \(\mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6} \)), are composed of molecules rather than ions. These compounds dissolve in water through hydrogen bonding, but their molecules remain intact. Although both KF and glucose dissolve in water, their dissolution processes differ significantly.

Hydration

Hydration is a fascinating and essential concept in chemistry that describes the interaction between water and solute particles. When ionic compounds dissolve, their ions become surrounded by water molecules. This process is known as hydration.
Water molecules, due to their polar nature, align such that the negative end of the molecule (oxygen) is near positively charged ions, and the positive end (hydrogens) is close to negatively charged ions. This alignment stabilizes the ions in solution and aids in the dissolution process.
For example, when you dissolve rubidium chloride (RbCl) in water, you witness hydration firsthand as the robust hydration energy of water breaks the ionic bonds in RbCl, resulting in free floating rubidium and chloride ions in the solution. This phenomenon is crucial for understanding how solutions are formed and function.

Dissolution

Dissolution is the process where solutes incorporate into a solvent to form a solution, and it's influenced by the nature of the solute and solvent.
When a substance dissolves, its particles disperse uniformly within the solvent. For example, nitric acid (HNO3) dissolves in water through ionization, forming hydronium (H+) and nitrate (NO3-) ions, thereby influencing the solution's properties significantly by making it acidic.
Conversely, carbon monoxide (CO), due to its nonpolar nature, shows limited dissolution in water. Lacking strong interactions with water, it remains largely undissolved, with no significant alteration to the water's pH levels. Understanding dissolution helps predict behaviour of substances in mixtures and is essential in fields like pharmaceuticals and chemical engineering.