Practice question

In alcoholic precipitation, DNA hydration is critical for solubility. Water molecules form hydration shell around negatively charged phosphates, keeping DNA hydrophilic and soluble. Addition of ethanol lowers dielectric constant of medium, reducing water activity and allowing monovalent cations to neutralize phosphates. This strips hydration shell, exposes hydrophobic nitrogenous bases, and makes DNA more hydrophobic and less soluble in polar solvent. Aggregation and precipitation follow. DNA does not become more hydrophilic, denatured at room temperature precipitation, or ionized further; hydrophobicity increase drives insolubility and aggregation in alcohol.