Question

why is the vapor pressure of a solution lower than the vapor pressure of the pure solvent? a because colloidal dispersion interferes with surface tension b because fewer solvent molecules are present on the surface c because the particles on the surface have less energy d because increased intermolecular forces prevent solvent molecules from evaporating question 12 which of the following solutions has the highest boiling - point? a 0.5 m na₂so₄ b 0.5 m c₆h₁₂o₆ c 0.5 m kbr d 0.5 m caco₃

Explanation:

Question 1: Why is the vapor pressure of a solution lower than the vapor pressure of the pure solvent?

In a solution, solute particles occupy some surface - area. This reduces the number of solvent molecules at the surface available for evaporation, thus lowering the vapor pressure.

The boiling - point elevation ($\Delta T_b = iK_bm$) depends on the van't Hoff factor ($i$) and molality ($m$). For a given molality, the solution with the highest $i$ value has the highest boiling - point elevation. $Na_2SO_4$ dissociates into 3 ions ($2Na^+ + SO_4^{2 - }$), $C_6H_{12}O_6$ is a non - electrolyte ($i = 1$), $KBr$ dissociates into 2 ions ($K^+ + Br^-$), and $CaCO_3$ is a sparingly soluble salt. Assuming complete dissociation for soluble salts, $Na_2SO_4$ with $i = 3$ will have the highest boiling point among these at the same molality.

Answer:

B. because fewer solvent molecules are present on the surface

Question 2: Which of the following solutions has the highest boiling point?