122ch13e

# 122ch13e - 46 13.65 Colligative properties depend on the...

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46 13.65) Colligative properties depend on the concentration of particles in solution. P A = X A A , ) P = X solute solvent , ) T f = i K f m , ) T b = i K b m , A = i M R T In the last 3 equations, the “ i ” is the number of particles in the formula for the substance. i = # solute particles in solution - integer for ideal behavior i = 1 for a non-dissociating or non-ionizing compound (nonelectrolyte) = # particles (ions) resulting from the formula unit a) A 0.10 m aqueous NaCl solution has a higher boiling point than a 0.10 m aqueous C 6 H 12 O 6 solution. This is because the NaCl is ionic and when put in H 2 O it dissociates (comes apart) to form ions. It forms 2 ions, Na + and Cl , for every NaCl. Thus, 0.10 moles of NaCl will give 0.20 moles of ions (particles) in solution. The C 6 H 12 O 6 is a molecular non-ionizing solute and stays together as a single particle when it dissolves (as most, but not all, molecular substances do). So 0.10 moles of C 6 H 12 O 6 will give 0.10 moles of solute particles in solution. The boiling point elevation of a solution is directly related to the total moles of dissolved particles (b.p. increases). The NaCl solution will have a higher b.p. since its concentration of particles is greater than that of the C 6 H 12 O 6 Ideally, the 0.10 m NaCl solution should have twice the effect as the 0.10 m C 6 H 12 O 6 solution (the b.p. elevation should be twice as great).

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47 13.65) (cont.)
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122ch13e - 46 13.65 Colligative properties depend on the...

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