Q4. Name three pairs of liquids that NCERT says form nearly ideal solutions.
n-hexane and n-heptane; bromoethane and chloroethane; benzene and toluene (NCERT page 13).
Q5. Assertion: a mixture of ethanol and acetone has a higher vapour pressure than Raoult’s law predicts. Reason: acetone molecules break some of the hydrogen bonds between ethanol molecules. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: weaker interactions in the mixture let molecules escape more easily (NCERT page 14).
Q6. Two liquids, of pure vapour pressures 300 mm Hg and 500 mm Hg, are mixed in equal moles. The mixture’s vapour pressure is measured as 360 mm Hg. Is the deviation positive or negative?
Raoult’s law predicts 0.5 × 300 + 0.5 × 500 = 400 mm Hg. 360 mm Hg is lower, so the deviation is negative (NCERT Eq. (1.16), page 10).
Q7. Why can’t a maximum boiling azeotrope be separated into its components by fractional distillation?
At the azeotropic composition the liquid and vapour have the same composition, so boiling it does not change the composition (NCERT page 14).
Q8. In which kind of non-ideal solution would you expect the solution to cool on mixing?
One with positive deviation: weaker A–B attractions mean heat is absorbed on mixing, ΔmixH > 0. It is the usual pattern, not a strict rule (reasoned from NCERT pages 13–14; NCERT Exercise 1.14 asks how the sign of ΔmixH relates to the deviations).