Which of the following compound will have the highest vapor pressure?

• A. 0.45 m dinitrogen pentoxide
• B. 0.10 m aluminum chloride
• C. 0.50 m iron (III) perchlorate
• D. 0.15 m calcium phosphate
• E. 0.30 m Potassium sulfide

Answer: (B)

Verified step by step guidance

1. Understand that vapor pressure is influenced by the number of solute particles in solution. More particles generally lead to a lower vapor pressure due to the colligative property known as Raoult's Law.
2. Identify the van't Hoff factor (i) for each compound, which represents the number of particles the compound dissociates into in solution. For example, aluminum chloride (AlCl₃) dissociates into 4 ions: 1 Al³⁺ and 3 Cl⁻.
3. Calculate the effective molality for each compound by multiplying the given molality by the van't Hoff factor. This will give you an idea of the total concentration of particles in solution.
4. Compare the effective molalities: the compound with the lowest effective molality will have the highest vapor pressure, as fewer solute particles mean less lowering of the vapor pressure.
5. Determine which compound has the lowest effective molality and thus the highest vapor pressure. This will be the compound with the least number of dissociated particles in solution.