Based on the structural formulas, which of the following identifies the compound that is more solubl — Bonding Chemistry Question

STEPS:

1. Analyze the chemical structures of the two solutes:
* Ethane ($\text{C}_2\text{H}_6$): Consists of a nonpolar hydrocarbon chain containing only carbon-carbon ($\text{C–C}$) and carbon-hydrogen ($\text{C–H}$) single bonds. Because carbon and hydrogen have very similar electronegativities, ethane is a nonpolar molecule with an even distribution of electrical charge.
* Propanol ($\text{C}_3\text{H}_8\text{O}$): Contains a nonpolar hydrocarbon region paired with a highly polar hydroxyl group ($\text{–OH}$). The highly electronegative oxygen atom is covalently bonded to a hydrogen atom, creating a strong permanent dipole.

2. Understand the solvent properties of water ($\text{H}_2\text{O}$):
* Water is a highly polar solvent with a permanent molecular dipole. Because of the extreme electronegativity difference between oxygen and hydrogen, water molecules form a strong network of hydrogen bonds with one another.

3. Apply the thermodynamic rule of solubility ("Like Dissolves Like"):
* Solubility depends directly on the nature and strengths of the intermolecular forces that can form between the solute and the solvent molecules compared to the forces holding the pure substances together.
* To dissolve in water, solute molecules must be able to establish intermolecular attractions of comparable strength to water's existing hydrogen bonds.

4. Evaluate the solute-solvent interactions:
* Ethane in water: Nonpolar ethane molecules can only interact with polar water molecules through weak London dispersion forces (induced dipole-dipole interactions). These interactions are too weak to break and replace the strong hydrogen bonds between water molecules. Consequently, ethane is virtually insoluble in water.
* Propanol in water: The highly polar hydroxyl ($\text{–OH}$) group on propanol can form strong hydrogen bonds directly with the surrounding water molecules. These strong solute-solvent attractions easily integrate propanol into water's hydrogen-bonding network, making propanol highly soluble in water.

5. Conclude:
* Propanol is more soluble in water because its molecules can form hydrogen bonds with water molecules, whereas ethane molecules cannot. This confirms Option D is the correct answer.

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WHY_OTHERS_WRONG:

• Option A is incorrect: Ethane has fewer total valence electrons (14) than propanol (26), meaning ethane has a smaller and *less* polarizable electron cloud, not a more polarizable one. Furthermore, polarizability primarily affects London dispersion forces, which are much weaker than hydrogen-bonding attractions and do not lead to high solubility in water.
• Option B is incorrect: Although ethane molecules are smaller than propanol molecules, molecular size does not dictate solubility. Solubility is dominated by the chemical nature of the intermolecular forces between the solute and the solvent. Even though ethane is small, its nonpolar nature prevents it from forming favorable interactions with polar water.
• Option C is incorrect: Although propanol has a greater molecular mass than ethane, mass itself is not a factor that determines solubility. The presence of the polar hydroxyl ($\text{–OH}$) group allowing for hydrogen bonding is what drives solubility, not molecular weight.