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Questions and Answers
What is responsible for the freezing point depression observed in solutions?
Which property is directly proportional to the molality of the solute in a solution?
What type of substances are nonelectrolytes?
In terms of composition, what characterizes strong electrolytes?
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When can it be assumed that the substance being worked with is a nonelectrolyte?
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For problems related to freezing point depression and boiling point elevation, what should be kept an eye out for?
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Which property undergoes changes due to the addition of solutes to a solvent?
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What is the condition for a solute to exert any change on colligative properties?
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In an ideal solution, adding solutes typically results in an increase in which of the following?
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Which property tends to decrease in value when solutes are added to a solvent?
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What does the chemical potential of a solvent indicate?
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How does the addition of solutes affect the vapor pressure of a solvent?
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Study Notes
Freezing Point Depression
- Freezing point depression is a colligative property observed in solutions that results from the introduction of solute molecules to a solvent.
- The freezing points of solutions are all lower than that of the pure solvent.
- The freezing point depression is directly proportional to the molality of the solute.
- The freezing point depression equation is: ΔT_f = T_f(solvent) - T_f(solution) = K_f × m
- Where ΔT_f is the freezing point depression, T_f(solvent) is the freezing point of the solvent, T_f(solution) is the freezing point of the solution, K_f is the freezing point depression constant, and m is the molality.
Types of Solutes
- Nonelectrolytes are substances with no ions, only molecules.
- Strong electrolytes are composed mostly of ionic compounds and essentially all soluble ionic compounds form electrolytes.
Solving Problems
- If the substance is uniform and not ionic, it can be assumed to be a nonelectrolyte and the formulas can be used to solve problems.
- These equations work for both volatile and nonvolatile solutions.
- The vapor pressure does not affect the change in temperature.
Colligative Properties
- Adding solutes to an ideal solution results in a positive ΔS, an increase in entropy.
- The properties that undergo changes due to the addition of solutes to a solvent are known as colligative properties.
- Colligative properties are dependent on the number of solutes added, not on their identity.
- Examples of colligative properties are boiling point and freezing point.
Boiling Point Elevation and Freezing Point Depression
- The boiling point and freezing point of a pure solvent can be changed when added to a solution.
- The freezing point of the pure solvent may become lower, and the boiling point may become higher.
- The extent to which these changes occur can be found using the formulas: ΔT_f = -K_f × m and ΔT_b = K_b × m.
Conditions for Colligative Properties
- The solute must fulfill two conditions to exert a change on colligative properties: it must not contribute to the vapor pressure of the solution, and it must remain suspended in the solution even during phase changes.
Chemical Potential
- The chemical potential of the solvent is lower when solutes are added.
- Chemical potential is the molar Gibb's energy that one mole of solvent is able to contribute to a mixture.
- The higher the chemical potential of a solvent is, the more it is able to drive the reaction forward.
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Description
Test your knowledge on freezing point depression, a colligative property observed in solutions due to the introduction of solute molecules. Understand the relationship between freezing point depression and solute molality in solutions.
