Q4. Two volatile liquids with pure vapour pressures 450 mm Hg and 700 mm Hg form an ideal solution. What are the lowest and highest possible values of its total vapour pressure?
450 mm Hg (pure less volatile liquid) and 700 mm Hg (pure more volatile liquid); every mixture lies on the straight line between them (NCERT page 10).
Q5. In an ideal solution of liquids 1 and 2, p10 = 200 mm Hg, p20 = 400 mm Hg and x2 = 0.25. Find y2, the mole fraction of 2 in the vapour.
p2 = 0.25 × 400 = 100; p1 = 0.75 × 200 = 150; ptotal = 250 mm Hg. y2 = 100/250 = 0.40 (NCERT Eqs. (1.12)–(1.19), pages 10–11).
Q6. Assertion: Raoult’s law is a special case of Henry’s law. Reason: in both, the partial pressure of a volatile component is proportional to its mole fraction, and Raoult’s constant is p10. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion (NCERT page 12).
Q7. The vapour pressure of a solvent falls from 640 mm Hg to 600 mm Hg when a non-volatile solute is added. Find the mole fraction of the solute.
x1 = 600/640 = 0.9375, so x2 = 1 − 0.9375 = 0.0625 (NCERT Eq. (1.20), page 13).
Q8. Name two solutions of solids in liquids that NCERT lists in which the solvent is not water.
Iodine in carbon disulphide and sulphur in carbon disulphide (NCERT page 12).