Question

Water is added to liquid isopropanol (a polar liquid) to form a solution of rubbing alcohol. Describe what happens on the molecular level as the water dissolves in the isopropanol. Select the correct step order from the drop-down menu for each step listed.

The polar isopropanol molecules are attracted to the polar water molecules at the surface of the water.

The water molecules spread evenly throughout the solution.

The water molecules are carried into the solution.

The isopropanol molecules surround the water molecules.

Answer 1

Correct order (what happens, step by step):

1. The polar isopropanol molecules are attracted to the polar water molecules at the surface of the water.
2. The isopropanol molecules surround the water molecules.
3. The water molecules are carried into the solution.
4. The water molecules spread evenly throughout the solution.

Brief explanation: Isopropanol and water are both polar and form hydrogen bonds/dipole–dipole attractions. At the interface the alcohol molecules are attracted to water; they form a solvation shell (surrounding the water molecules) as water moves into the alcohol phase. Random molecular motion (diffusion) and bulk mixing carry molecules into the bulk solution, and over time diffusion and entropy cause the water molecules to spread evenly (a homogeneous rubbing-alcohol solution).