Raoult's Law — Vapour Pressure of Solutions

In an ideal solution each volatile component contributes a partial pressure equal to its pure vapour pressure times its mole fraction (pᴬ = xᴬ·p°ᴬ), so the total is a straight line between the two pure liquids. Students vary the mole fraction and the two pure vapour pressures, and toggle ideal / positive / negative deviation to see p_total bulge above or dip below the ideal line as A–B attractions differ from A–A and B–B. Dropping p°_B to near zero recovers the non-volatile-solute case — the relative lowering that underlies every colligative property — and the vapour composition y_A shows the vapour is always richer in the more volatile liquid.