9: Osmotic Pressure and Solvation Concepts

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Questions and Answers

What does osmotic pressure measure?

  • The pressure needed to counteract osmotic flow (correct)
  • The volume of the solution
  • The weight of the solvent
  • The temperature of the solution

A solution with a higher osmotic pressure is considered hypotonic.

False (B)

What is the definition of osmotic flow?

The movement of solvent across a membrane to equalize solute concentrations.

If the osmotic pressure of a solution is less than that of another solution, it is classified as _______.

<p>hypotonic</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Isotonic = Solutions with the same osmotic pressure Hypertonic = Solution with higher osmotic pressure Hypotonic = Solution with lower osmotic pressure Van't Hoff factor = Factor used to calculate osmotic pressure</p> Signup and view all the answers

What is the definition of a solution?

<p>A homogeneous mixture of solvent and solutes (A)</p> Signup and view all the answers

The spontaneous process of dissolving a solute occurs when the change in Gibbs free energy is greater than zero.

<p>False (B)</p> Signup and view all the answers

What is the primary solvent discussed in the lecture?

<p>water</p> Signup and view all the answers

The process of forming a solution involves the change in _____ free energy.

<p>Gibbs</p> Signup and view all the answers

When does a solute typically dissolve in a solvent?

<p>When the change in Gibbs free energy is less than zero (C)</p> Signup and view all the answers

What is an essential factor that influences the solvation process?

<p>Intermolecular interactions (D)</p> Signup and view all the answers

Match the intermolecular interaction with its description:

<p>Van der Waals = Dispersion and dipole–dipole interactions Hydrogen bonding = Strong attractive force between hydrogen and electronegative atom Ion–dipole = Attraction between ions and polar molecules Dipole–dipole = Interaction between molecules that have permanent dipoles</p> Signup and view all the answers

If the enthalpy change during solvation is positive, it indicates that the solution will form regardless of solute concentration.

<p>False (B)</p> Signup and view all the answers

What happens during the mixing step of solvation?

<p>The separated solvent and solute combine to form a solution.</p> Signup and view all the answers

The solvation process involves the interaction between solute and solvent molecules.

<p>True (A)</p> Signup and view all the answers

If the total enthalpy change, ∆H_solution, is less than zero, the process is ______.

<p>exothermic</p> Signup and view all the answers

What must be true for a process to be spontaneous in the context of solutions?

<p>Gibbs free energy change is less than zero.</p> Signup and view all the answers

Match the terms related to solvation with their definitions:

<p>Exothermic = Energy-releasing process Endothermic = Energy-absorbing process Miscible = Completely dissolve in each other Insoluble = Cannot dissolve in a solvent</p> Signup and view all the answers

Which statement explains why solvation is more likely to occur at high temperatures?

<p>Higher temperature increases disorder among solute and solvent. (A)</p> Signup and view all the answers

Insoluble solutes can dissolve if enough solvation energy is provided.

<p>True (A)</p> Signup and view all the answers

What is the significance of the separate solvent and solute terms in the solvation equation?

<p>They represent the individual components before forming a solution.</p> Signup and view all the answers

What is a characteristic of an ideal gas?

<p>It exhibits no intermolecular interactions. (C)</p> Signup and view all the answers

In an ideal solution, all intermolecular interactions are different.

<p>False (B)</p> Signup and view all the answers

What happens when the solute-solvent interaction is greater than the solute-solute interaction in a solution?

<p>The solution behaves ideally and influences colligative properties</p> Signup and view all the answers

In an ideal solution, solute-solvent interactions are __________ compared to solute-solute interactions.

<p>equal</p> Signup and view all the answers

Match the following interactions with their characteristics:

<p>Ideal gas = No intermolecular interactions Ideal solution = Identical intermolecular interactions Solute-solvent interaction = Greater than solute-solute interaction Colligative properties = Depend on the number of solute particles</p> Signup and view all the answers

What happens if the solute-solvent interactions are less than the solute-solute interactions?

<p>The solution exhibits non-ideal behavior. (A)</p> Signup and view all the answers

Colligative properties depend on the type of solute particles in a solution.

<p>False (B)</p> Signup and view all the answers

What defines the behavior of an ideal solution?

<p>All intermolecular interactions being identical.</p> Signup and view all the answers

What does molarity measure?

<p>Moles of solute per liter of solution (B)</p> Signup and view all the answers

Molality is defined as the mass of solute in grams per liter of solution.

<p>False (B)</p> Signup and view all the answers

What is the formula for calculating parts per billion (ppb)?

<p>mass solute / total mass × 10^9</p> Signup and view all the answers

The change in properties of a solvent due to the addition of a solute is called __________ properties.

<p>colligative</p> Signup and view all the answers

Which of the following represents the correct formula for ppm?

<p>mass solute / total mass × 10^6 (C)</p> Signup and view all the answers

Colligative properties depend only on the chemical identity of the solute.

<p>False (B)</p> Signup and view all the answers

How does adding solute affect the boiling point of a solvent?

<p>It raises the boiling point.</p> Signup and view all the answers

What is the main purpose of anti-icing treatments?

<p>To lower the freezing point of water (A)</p> Signup and view all the answers

The van’t Hoff factor is used in calculating freezing-point depression.

<p>True (A)</p> Signup and view all the answers

What is the formula for calculating freezing-point depression?

<p>∆Tf = -Kf * m</p> Signup and view all the answers

The solution with 25% ethylene glycol in water is __________ molal.

<p>5.37</p> Signup and view all the answers

Which of the following describes a semi-permeable membrane?

<p>Allows only solvent to pass through (A)</p> Signup and view all the answers

Osmosis occurs when solute particles move through a semi-permeable membrane.

<p>False (B)</p> Signup and view all the answers

List one example of a solute that is commonly used in automotive anti-freeze.

<p>Ethylene glycol</p> Signup and view all the answers

Flashcards

Change in Gibbs Free Energy (∆G) of Solution Formation

A change in Gibbs free energy that occurs when a solution is formed by mixing a solute uniformly in a solvent.

Spontaneous Solution Formation

The process of forming a solution is spontaneous if the change in Gibbs free energy (∆G) is negative.

Enthalpy Change (∆H) of Solution Formation

The change in enthalpy (∆H) during solution formation.

Entropy Change (∆S) of Solution Formation

The change in entropy (∆S) during solution formation.

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Solution

A homogeneous mixture where a solute is uniformly dispersed in a solvent.

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Solute

The substance being dissolved in a solution.

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Solvent

The substance that dissolves the solute in a solution.

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Solvation

The process where solute molecules are surrounded by solvent molecules.

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Separating Solvent

The process of separating solvent molecules from each other.

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Separating Solute

The process of separating solute molecules from each other.

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Mixing Solvent and Solute

The process of mixing separated solvent and solute molecules to form a solution.

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Total Enthalpy Change

The total enthalpy change during the solvation process, encompassing the energy changes involved in separating solvent, separating solute, and mixing them together.

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Enthalpy Change of Solvent Separation

The energy released or absorbed during the separation of solvent molecules.

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Enthalpy Change of Solute Separation

The energy released or absorbed during the separation of solute molecules.

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Enthalpy Change of Mixing

The energy released or absorbed during the mixing of separated solvent and solute molecules.

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Enthalpy Change of Solvation

The change in enthalpy during the solvation process, representing the overall energy change involved in forming a solution.

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Colligative Property

A property of a solution that depends only on the concentration of the solute, not its identity.

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Solution Formation

The process of adding a solute to a solvent to form a solution.

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Gibbs Free Energy of Solution Formation (∆G)

The change in Gibbs free energy (∆G) that occurs when a solution is formed by mixing a solute uniformly in a solvent.

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Enthalpy Change of Solution Formation (∆H)

The change in enthalpy (∆H) during solution formation.

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Osmotic Pressure

The pressure required to counteract the osmotic flow of a solvent across a semipermeable membrane, preventing the net movement of the solvent from a region of higher concentration to a region of lower concentration.

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Isotonic

A solution with the same osmotic pressure as another solution. There is no net movement of solvent between them.

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Hypertonic

A solution with a higher osmotic pressure than another solution. Solvent will flow out of the hypotonic solution into the hypertonic solution.

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Hypotonic

A solution with a lower osmotic pressure than another solution. Solvent will flow into the hypotonic solution from the hypertonic solution.

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Osmosis

The process by which solvent molecules move across a semipermeable membrane from a region of higher solvent (lower solute) concentration to a region of lower solvent (higher solute) concentration in order to equalize the concentrations on both sides.

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Freezing-Point Depression

The decrease in the freezing point of a solvent when a solute is added. The extent of depression is directly proportional to the molality of the solute.

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Molality

A measure of the concentration of a solute in a solution, defined as the number of moles of solute per kilogram of solvent.

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Molal Freezing Point Depression Constant (Kf)

A constant that relates the molality of a solute to the freezing point depression. It's specific to the solvent.

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Freezing Point Depression (∆Tf)

The change in the freezing point of a solution compared to the pure solvent.

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van't Hoff Factor (i)

A factor that accounts for the dissociation of a solute into ions in solution. It reflects the number of particles a solute produces when dissolved.

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Vapor Pressure Lowering

A solution containing a non-volatile solute has a lower vapor pressure than the pure solvent. This means it requires a higher temperature to boil.

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Ideal Solution

A solution where all intermolecular interactions between solute and solvent molecules are assumed to be equal, regardless of the type of interaction (solute-solute, solvent-solvent, or solute-solvent).

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Favorable enthalpy change

Solution where the solute-solvent interactions are stronger than either the solute-solute or solvent-solvent interactions. The enthalpy change of solution formation is negative, indicating heat is released.

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Enthalpy change of solution formation

The sum of the enthalpy changes involved in breaking apart solute and solvent molecules and then forming solute-solvent interactions during solution formation.

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Unfavorable enthalpy change

Occur when the energy released upon mixing solute and solvent is less than the energy used to separate the solute and solvent molecules. The enthalpy change of solution formation is positive, indicating heat is absorbed.

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Endothermic solution formation

Solutions where solute-solvent interactions are weaker than either the solute-solute or solvent-solvent interactions. The enthalpy change of solution formation is positive, indicating heat is absorbed.

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Exothermic solution formation

Solutions where solute-solvent interactions are stronger than either the solute-solute or solvent-solvent interactions. The enthalpy change of solution formation is negative, indicating heat is released.

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Ideal gas

Describing the interaction between solute and solvent molecules during solution formation. This interaction can be strong or weak, leading to different enthalpy changes and solution behaviors.

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Study Notes

Lecture Announcements

  • Today's Topics: Properties of Solutions (Brown Ch. 13)
  • Specific Topics: The Solution Process, Saturated Solutions and Solubility, Factors Affecting Solubility, Expressing Solution Concentration, Colligative Properties
  • Problem Sets: Problem Set 8 due tomorrow, upload on Moodle. Problem Set 9 posted on Moodle; due before Exercise #10 next week.
  • Study Center: Wednesdays 6:00 PM - 8:00 PM in ETA F 5
  • Office Hours: Prof. Norris and Brisby, Thursdays 5:00 PM - 6:00 PM in LEE P 210
  • Resources: Five practice exams available.

Lecture 10

  • Next Week's Topics: Chemical Kinetics (Brown Ch. 14)
  • Specific Topics: Factors That Affect Reaction Rates, Reaction Rates, Concentration and Rate Laws, The Change of Concentration with Time

Red Thread

  • Course Summary: A conceptual overview, connecting topics previously covered with new material.

  • Progression: Intro → Gases → Solutions → Thermo → other chemistry topics like Catalysis, Acid-Base, Equilibrium, Batteries, etc.

  • Overall Goal: Establish deeper understanding of how molecules interact and affect properties of substances

Review of Lecture 8

  • Intermolecular Interactions and Liquids: Key concepts included Van der Waals interactions, molecular dipoles, hydrogen bonding, ion-dipole interactions, and polar solvents.
  • Properties of Liquids: Viscosity, surface tension, vapor pressure, phase changes, heat of fusion, heat of vaporization, heat of sublimation, heating curves, phase diagrams, and the Clausius-Clapeyron equation.

Review (Focus on Intermolecular Forces)

  • Hierarchy of Intermolecular Forces (strongest to weakest): Ionic bonding, Ion-dipole forces, hydrogen bonding, dipole-dipole forces, dispersion forces (van der Waals)
  • Examples of compounds/materials for each type of intermolecular force . (e.g., NaCl, polar solvents, NH3, CH3OH, CH4, Br2)

Lecture 3: Properties of Solutions

  • Definition of Solution: Solvent + Solute; homogenous mixture
  • Solvation Process: Process of dissolving substances in water (or other solvents). Also known as hydration.
  • Key Questions: When do substances dissolve? How much dissolves? What are the properties of solutions?

Thermodynamics of Solutions

  • Definition: Change in Gibbs free energy to form a solution.
  • Spontaneity: Solutions are spontaneous if the change in Gibbs free energy is less than 0.
  • Relationship to Entropy and Enthalpy: ΔG = ΔH - TΔS. ΔSsoln is the change in entropy in mixing solute and solvent, typically positive. The change in enthalpy ΔHsoln, depends on the intermolecular interactions (solute-solute, solute-solvent, solvent-solvent).

Enthalpy Changes During Solvation

  • Breaking Intermolecular Forces: Solvation involves breaking solute, solvent, and solute/solvent interactions.
  • Steps of the process: Separate solvent, separate solute, mix separated solvent and solute.
  • Exothermic vs. Endothermic: Enthalpy changes of solution formation (ΔHsoln) can be positive (endothermic).

Solubility

  • Definition: Maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature.
  • Factors: Solubility depends on a multitude of factors including: temperature, pressure, and the nature of the solvent and solute.
  • Solid vs Liquid Solubility: Solutes can be solids or liquids, and solubility behavior can be different for each type.
  • "Like Dissolves Like" (general rule): Polar substances tend to dissolve in polar solvents, and nonpolar substances tend to dissolve in nonpolar solvents

Other Factors Affecting Solubility

  • Pressure: Solubility of gases increases with pressure (Henry's Law).
  • Temperature: Solubility of many solids increases with temperature, whereas solubility of gases decreases with increasing temperature.
  • Example: How dissolving carbon dioxide or other gases in water or other solvents is affected by temperature or pressure .

Expressions for Concentration

  • Qualitative: Dilute, Concentrated
  • Quantitative Units: Mole fraction (X), Mass %, Molarity (M), Molality (m), ppm, ppb.

How Does Solute Affect Properties of the Solvent (Colligative Properties)

  • Boiling Point Elevation: Solute increases the boiling point of the solvent (measured using a change in temperature ΔTb, dependent on molality 'm' of solute)
  • Vapor Pressure Lowering: Solute lowers the vapor pressure of the solvent by Raoult's Law
  • Freezing Point Depression: Solute decreases the freezing point of the solvent (measured using a change in temperature from the pure solvent ΔTf).

Osmosis

  • Semi-permeable membrane: Allows the passage of the solvent/solute (water) but not the solvent.
  • Osmotic flow occurs when the solvent diffuses to equalize the concentration across a semi-permeable membrane.
  • Osmotic pressure : Counteracting osmotic flow, measures the pressure required to prevent more solvent movement.

Ideal Gas vs Ideal Solutions

  • Ideal Gas: No intermolecular forces.
  • Ideal Solution: Intermolecular forces are identical in each component of the solution (solute, solvent).

Determining Molecular Weight

  • Application of osmotic pressure (Π) to find the molar mass (MW) of a solute.

Antifreeze Proteins (AFPs)

  • Mechanism of action: AFPs function differently than other antifreeze agents by blocking ice nucleation, not by lowering the freezing point.
  • Non-colligative effect
  • Kinetics-based mechanism is important

Summary of What We Learned

  • Thermodynamics of Solutions (ΔG, ΔH, ΔS): Crucial for assessing the spontaneity and energy changes in mixing processes.
  • Solubility Concepts: Various factors impacting solubility (polarity, T, P).
  • Expressions of Concentration: Essential ways to quantify solute levels in solutions.
  • Colligative Properties: Properties altering with concentration (BP elevation, VP lowering, FP depression, Osmosis).

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