Vapor Pressure Lowering (13.3.1) Flashcards
• A colligative property is one that depends on the concentration of the solute but not on the nature of the solute.
• A colligative property is one that depends on the concentration of the solute but not on the nature of the solute.
• Raoult’s law states that the vapor pressure of the solvent decreases linearly as the mole fraction of the solute increases.
• Raoult’s law states that the vapor pressure of the solvent decreases linearly as the mole fraction of the solute increases.
Which statement about colligative properties is not correct?
Two solutions with slightly different mole fractions for their solutes can still have the same value for a colligative property. (C)
Colligative properties have one requirement: they only concern solutions that have the same mole fraction of solute, regardless of which solute may be involved.
A solution is made up of mixing 3.81 g of naphthalene (C10H8 ) and 87.5 g benzene (C6H6 ). What is the vapor pressure of benzene above the solution?
Vapor pressure of benzene (P°solvent ) is 0.1252 atm.
The molecular weight of naphthalene is 128.17 g / mol and the molecular weight of benzene is 78.0 g / mol.
0.122 atm (C)
Look at the plot and the equations for Raoult’s law. Which statement is not correct with respect to Raoult’s law?
If you increase the concentration of the solvent, Xsolvent, the vapor pressure of the solute, Psolute, increases. (D)
As the mole fraction of the solvent increases, the vapor pressure of the solute will decrease rather than increase.
A simple experiment proves Raoult’s law that the presence of solute molecules in a solution lowers the vapor pressure. Look at the diagram representing a closed system.
You can see that, after time, the pure water in the closed system evaporated and condensed into the sugar water. Which statement about this experiment is not true?
The pure water has a greater vapor pressure. Water molecules will evaporate from the solution that has less vapor pressure. (D)
Which of the following statements about vapor pressure is not correct?
A solution that contains a nonvolatile solute will always have a higher vapor pressure than the solvent in pure form (i.e., the pure solvent). (D)
Look at the two plots showing the deviations in Raoult’s law.
Which statement about these plots is not correct?
The plot indicates that, at any solute concentration, the vapor pressure of the endothermic solution reaction is always greater than the other two vapor pressure values for the other types of solutions. (B)
What is Raoult’s law?
Raoult’s law states that the vapor pressure of the solvent in a solution is directly proportional to the mole fraction of the solvent. (A)
Which of the following is not an example of a colligative property?
solute-concentration elevation (D)
What is a colligative property?
a property that only depends on the number of solute particles present in a given amount of solution (C)
A colligative property does not depend upon chemical composition; it is only a function of the concentration of solute in the solution. For example, a solution with a 0.01 m concentration of one solute will have the same value for a colligative property as the same solution would have with a 0.01 m concentration of a different solute.
An aqueous solution of glucose, in which the mole fraction of glucose solute is 0.01, has the same vapor pressure, boiling point, and freezing point as an aqueous solution of sucrose, in which the mole fraction of sucrose solute is also 0.01. Which statement best describes the properties of these two solutions?
The two solutions have colligative properties. This is because the three effects mentioned (vapor pressure, boiling point, freezing point) depend exclusively on the number of solute particles in solution. (B)
