The high solubility of ethanol in water is due to?

Step 1: Analyze the question We need the reason ethanol (C₂H₅OH) dissolves so well in water.

Step 2: The concept "Like dissolves like." Solubility depends on how well the attractions between solute and solvent molecules compare with the attractions within each pure substance. Water is a polar molecule that forms hydrogen bonds. Hydrogen bonding occurs when hydrogen is attached to a highly electronegative atom (F, O, or N) and is attracted to a lone pair on another such atom.

Step 3: Apply it to ethanol

• Ethanol has an -OH (hydroxyl) group, so its structure is CH₃CH₂–O–H.
• The O–H bond is highly polar, so the hydrogen is partially positive and the oxygen is partially negative.
• The -OH group of ethanol forms hydrogen bonds with the water molecules (O–H···O).
• These new ethanol-water hydrogen bonds are about as strong as the hydrogen bonds in pure water, so the two liquids mix freely (they are miscible).

Step 4: Check the other options

• A. Low boiling point: This describes volatility and has no bearing on solubility.
• B. Low freezing point: This is also unrelated to dissolving.
• C. Covalent nature: Many covalent compounds, such as hexane and methane, do not dissolve in water, so being covalent does not explain solubility.
• D. Hydrogen bonding: This is the specific interaction between ethanol and water, so it is correct.

Answer: D. Hydrogen bonding

Exam tip: When you see a small molecule with an -OH or -NH₂ group dissolving in water (alcohols, small amines, sugars), think "hydrogen bonding." Remember that as the carbon chain gets longer, solubility drops because the non-polar part dominates.