Mix equal volumes of high-proof ethanol (Everclear) and water and something counterintuitive happens: the total volume decreases. This is called volume contraction, and it’s a direct result of molecular-scale interactions—not measurement error. Ethanol molecules are amphiphilic: they have a polar hydroxyl (-OH) group and a nonpolar ethyl chain. Water is a highly polar, hydrogen-bonded network. When you mix the two, ethanol molecules insert into the water structure and form strong hydrogen bonds with water molecules. This allows the mixture to pack more efficiently than either liquid alone. In thermodynamic terms, the mixture exhibits a negative excess molar volume—the real volume is lower than the ideal sum. Now add salt (e.g., NaCl) to the mixture. The ions compete for water molecules, strongly coordinating with them through ion-dipole interactions. This disrupts ethanol–water hydrogen bonding and reduces ethanol’s solubility in the aqueous phase. The result is a salting-out effect:...