Question

Choose the aqueous solution with the lowest vapor pressure. These are all solutions of nonvolatile solutes, and you should assume ideal Van't Hoff factors where applicable.

Options:
a) 0.120 M C₂H₆O₂
b) 0.060 M Li₂NO₃
c) 0.030 M RbC₂H₃O₂
d) 0.040 M (NH₄)₂SO₄

Answer 1

The aqueous solution with the lowest vapor pressure is 0.060 M Li₂NO₃ because it will produce the greatest number of solute particles when dissociated, assuming ideal behavior of a van't Hoff factor of 3.

Step-by-step explanation:

The aqueous solution with the lowest vapor pressure among the given options will be the one with the highest solute particles in solution, hence exerting the greatest van't Hoff factor effect. To assess this, you need to calculate the total number of moles of particles in each solution produced from each solute.

For the options given:

• 0.120 M C₂H₆O₂ (ethylene glycol) is a non-electrolyte, its van't Hoff factor (i) is 1, so total moles of particles = 0.120 M * 1 = 0.120.
• 0.060 M Li₂NO₃ (Lithium nitrate) dissociates into 3 ions (2 Li+ and 1 NO₃−), i = 3, total moles of particles = 0.060 M * 3 = 0.180.
• 0.030 M RbC₂H₃O₂ (Rubidium acetate) dissociates into 2 ions (1 Rb+ and 1 C₂H₃O₂−), i = 2, total moles of particles = 0.030 M * 2 = 0.060.
• 0.040 M (NH₄)₂SO₄ (Ammonium sulfate) dissociates into 3 ions (2 NH₄+ and 1 SO₄−), i = 3, total moles of particles = 0.040 M * 3 = 0.120.

Comparing the total moles of solute particles, 0.060 M Li₂NO₃ will have the lowest vapor pressure because it will produce the greatest number of solute particles given the ideal van't Hoff factor.