Q4. What value of i would you expect for (a) glucose in water, (b) MgCl2 fully dissociated in water, (c) a solute that fully forms dimers?
(a) 1; (b) 3, since MgCl2 gives three ions; (c) 0.5 (NCERT page 24).
Q5. Assertion: the molar mass of NaCl found from the depression of the freezing point of its aqueous solution is less than 58.5 g mol−1. Reason: NaCl dissociates into ions in water. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: dissociation raises the number of particles, so the experimental molar mass is lower than the true value (NCERT pages 23–24).
Q6. Find the osmotic pressure at 300 K of a solution of 0.010 mol of K2SO4 in 1 L, taking complete dissociation (R = 0.083 L bar mol−1 K−1).
i = 3, so Π = 3 × 0.010 × 0.083 × 300 = 0.747 bar, about 0.75 bar (NCERT page 24).
Q7. A weak acid HA in a 0.01 m aqueous solution has i = 1.05. Find its degree of dissociation in the ideal particle-count model.
i = 1 + x for two ions, so x = 0.05, or 5% (NCERT page 26).
Q8. Why do the measured values of i for MgSO4 in NCERT Table 1.4 fall further short of 2 than those for NaCl?
Mg2+ and SO42− are doubly charged, so they attract each other more strongly, and fewer behave as independent particles (reasoned from the interionic attractions NCERT mentions on page 23).
Q9. For ideal solutions at the same temperature and a membrane retaining both solutes, which glucose concentration is isotonic with 0.10 M NaCl, taking complete dissociation and ignoring interionic effects?
Isotonic solutions have equal i × concentration: 1 × c = 2 × 0.10, so c = 0.20 M (reasoned from NCERT page 24).
Q10. What is i for K4[Fe(CN)6] fully dissociated in water?
5: four K+ ions and one [Fe(CN)6]4− ion, which stays whole (reasoned from NCERT page 24).