When a nonvolatile solute is added to a volatile solvent, the solution vapor pressure __________, the boiling point __________, the freezing point __________, and the osmotic pressure across a semipermeable membrane __________.
A) decreases, decreases, increases, decreases
B) increases, decreases, increases, decreases
C) decreases, increases, decreases, increases
D) increases, increases, decreases, increases
E) decreases, increases, decreases, decreases

Question

Quizplus · Accepted Answer

When a nonvolatile solute is added to a volatile solvent, the solution vapor pressure decreases due to the decrease in the number of solvent molecules at the surface of the solution. This is Raoult's law. The boiling point increases because the presence of the solute makes it harder for the solvent molecules to escape into the vapor phase, so they need more energy to boil. This is the boiling point elevation phenomenon. The freezing point decreases because the solute disrupts the crystal lattice structure of the solvent, making it more difficult for the solvent molecules to form a solid. This is the freezing point depression phenomenon. Finally, the osmotic pressure across a semipermeable membrane increases because the solute causes the solvent to flow from an area of higher concentration to an area of lower concentration to balance the concentration of the solute on both sides of the membrane. This is the osmotic pressure phenomenon. Therefore, the correct answer is C.

When a Nonvolatile Solute Is Added to a Volatile Solvent