[VISUAL] 49. The table above shows the structural formulas and molar masses for three different comp — States of Matter Chemistry Question

STEPS:

1. Analyze the chemical structures of each compound provided in the table:
* Butane ($\text{C}_4\text{H}_{10}$): A straight-chain hydrocarbon consisting entirely of nonpolar $\text{C}-\text{H}$ and $\text{C}-\text{C}$ bonds.
* Acetone ($\text{CH}_3\text{COCH}_3$): A symmetric, polar ketone containing a highly electronegative carbonyl oxygen double-bonded to carbon ($\text{C}=\text{O}$).
* 1-propanol ($\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}$): An alcohol containing a highly polar hydroxyl group ($-\text{OH}$).
2. Determine the types of intermolecular forces (IMFs) present in each liquid:
* Butane: Because the electronegativity difference between carbon and hydrogen is negligible, butane is a nonpolar molecule. Thus, butane molecules are held together in the liquid phase solely by weak London dispersion forces (LDFs).
* Acetone: Due to the polar carbonyl group, the molecule has a permanent net dipole moment. It experiences relatively strong dipole-dipole attractions in addition to LDFs.
* 1-propanol: Because a hydrogen atom is directly bonded to a highly electronegative oxygen atom in the hydroxyl group, 1-propanol molecules are capable of forming extremely strong intermolecular hydrogen bonds (the strongest type of IMF among these three substances) in addition to dipole-dipole attractions and LDFs.
3. Relate IMF strength to boiling point:
* The boiling point of a substance represents the temperature at which the average kinetic energy of the molecules is sufficient to completely overcome the intermolecular attractions holding them together in the liquid phase.
* Stronger intermolecular forces require a significantly larger input of thermal energy to disrupt, directly resulting in a higher boiling point.
4. Rank the compounds in order of increasing boiling point:
* Lowest boiling point: Butane, because it possesses only weak London dispersion forces.
* Middle boiling point: Acetone, because its dipole-dipole attractions are stronger than butane's LDFs but weaker than hydrogen bonds.
* Highest boiling point: 1-propanol, because its intermolecular hydrogen-bonding network requires the greatest amount of thermal energy to overcome.
* Therefore, the correct increasing order of boiling points is Butane < acetone < 1-propanol, which corresponds to Option B.

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WHY_OTHERS_WRONG:

• Option A is incorrect: This option places acetone at a higher boiling point than 1-propanol. However, 1-propanol's capacity to form strong hydrogen bonds makes its intermolecular attractions much stronger than the dipole-dipole interactions found in acetone. Therefore, 1-propanol must have a higher boiling point than acetone.
• Option C is incorrect: This option completely reverses the correct order, claiming that the hydrogen-bonding 1-propanol has the lowest boiling point and the nonpolar butane has the highest boiling point.
• Option D is incorrect: This option incorrectly asserts that acetone and butane have equal boiling points. Although they have identical molar masses ($58.1\text{ g/mol}$) and thus comparable London dispersion forces, acetone's permanent dipole-dipole forces make its overall intermolecular attractions much stronger than butane's, giving it a significantly higher boiling point.