$word_{count}$: 200

For two IMMISCIBLE liquids, each exerts its own vapor pressure independently (NOT Raoult's law). Total vapor pressure = P(water) + P(compound). The mixture boils when this sum equals atmospheric pressure (1 atm), which occurs at a temperature BELOW either pure component's bp. This allows high-bp compounds to distill without decomposition. Requirements: (1) Immiscible with water, (2) Appreciable vapor pressure near 100 degrees C (steam-volatile), (3) Stable under steam conditions. Mass ratio in distillate: m$\frac{water}{m}$(compound) = [P(water) x MW(water)] / [P(compound) x MW(compound)]. Since MW(water) = 18 is small and most organic compounds have MW > 90, a large mass of water accompanies each gram of compound. Example: aniline (MW 93, P at 98 degrees C ≈ 5 kPa) + water (P at 98 degrees C ≈ 96 kPa): m$\frac{water}{m}$(aniline) = $\frac{96 x 18}{(5 x 93)}$ = 3.7 g water per g aniline. Applications: aniline, nitrobenzene, essential oils (clove, eucalyptus), terpenes. JEE tests the principle (why it works), conditions required, and mass ratio calculations.