Practice question

Ethanol precipitates DNA by altering solvent properties. Water has high dielectric constant of 80, shielding electrostatic attraction between negative phosphate groups and positive cations like Na+. Ethanol has dielectric constant around 24, dramatically lowering solvent polarity when mixed. This allows sodium ions from added salt to neutralize phosphate charges efficiently, reducing hydration shell and DNA solubility. DNA becomes less hydrophilic, aggregates, and precipitates. Ethanol does not lower pH significantly, increase hydrophilicity, or break disulfide bonds; its action is purely through dielectric and solubility reduction enabling aggregation.