Draw the Lewis structure of isopropyl alcohol (look in text). Is polar or nonpolar? What intermolecular forces does it have? If you are looking at a solution, how would you know if it is saturated or unsaturated?
The Correct Answer and Explanation is:
Correct Answer:
- Lewis structure of isopropyl alcohol (C₃H₈O) shows a central carbon atom bonded to a hydroxyl group (–OH) and two methyl groups (–CH₃).
- Polarity: Isopropyl alcohol is polar.
- Intermolecular forces: It exhibits hydrogen bonding, dipole-dipole interactions, and London dispersion forces.
- To determine if a solution is saturated or unsaturated: Add a small amount of solute. If it dissolves, the solution is unsaturated. If it does not, or settles at the bottom, the solution is saturated.
Detailed Explanation
Isopropyl alcohol, also known as 2-propanol, has the molecular formula C₃H₈O. The Lewis structure shows three carbon atoms: a central carbon (C-2) bonded to one hydroxyl group (–OH) and two methyl groups (–CH₃). Each carbon forms four bonds: either to hydrogen or other carbon atoms. The oxygen in the hydroxyl group forms two bonds—one to hydrogen and one to carbon—and has two lone pairs.
The presence of the hydroxyl group makes the molecule polar, due to the difference in electronegativity between oxygen and hydrogen, and the resulting dipole moment. The geometry around the oxygen atom is bent, enhancing the molecule’s polarity.
Because of its polarity, isopropyl alcohol can engage in hydrogen bonding, particularly through the –OH group. This is the strongest intermolecular force in the molecule. In addition to hydrogen bonding, dipole-dipole interactions occur between the partially positive hydrogen atoms and the partially negative oxygen atoms of adjacent molecules. Furthermore, London dispersion forces, which arise from temporary dipoles, are always present regardless of polarity.
To determine if a solution is saturated or unsaturated, add a small quantity of the solute to the solution. If the solute dissolves completely, the solution is unsaturated, indicating it can still hold more solute at that temperature. If the added solute does not dissolve and settles at the bottom, the solution is saturated, meaning it has reached its maximum solute capacity under current conditions. Temperature can influence solubility, so observations should be made at constant conditions for accurate assessment.
