Introduction to Solutions
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Questions and Answers

What is the expression for the degree of dissociation, α, when dealing with an electrolyte of the type AB such as NaCl?

  • α = (2i - 1)
  • α = 1 - (i / 2)
  • α = (i + 1) / 2
  • α = (i - 1) / 2 (correct)

How is the total number of moles after association calculated when 1 mole of A associates with a degree of association α?

  • 1 - α - α/n
  • 1 - α + α/n (correct)
  • 1 - α + nα
  • 1 + α/n

In the context of colligative properties, how is the Van't Hoff factor, i, expressed after association?

  • i = 1 + α(n - 1)
  • i = α / (1 - α)
  • i = 1 - (α/n)
  • i = (1 - α + α/n) / 1 (correct)

For an electrolyte like CaCl2, what is the value of n in the context of its degree of dissociation?

<p>2 (A)</p> Signup and view all the answers

What is the general definition of the degree of association?

<p>Fraction of total moles of the substance which combine to form associated molecules (A)</p> Signup and view all the answers

What happens to the total vapor pressure in a solution exhibiting negative deviation compared to an ideal solution?

<p>It is less than the expected vapor pressure. (D)</p> Signup and view all the answers

Which of the following pairs of substances is an example of a negative deviation solution?

<p>Chloroform and nitric acid (A)</p> Signup and view all the answers

In solutions with negative deviation, how does the energy change during the mixing process?

<p>Energy is released, making it exothermic. (D)</p> Signup and view all the answers

What effect does heating have on the solubility of solutions exhibiting negative deviation?

<p>It decreases the solubility. (C)</p> Signup and view all the answers

How do the intermolecular forces in a mixture exhibiting negative deviation compare to those in pure components?

<p>They are stronger than in the pure components. (A)</p> Signup and view all the answers

What happens to ΔmixingV when two liquids with negative deviation are mixed?

<p>ΔmixingV becomes negative. (D)</p> Signup and view all the answers

Which of the following statements is true about solutions exhibiting positive deviation?

<p>The attractive forces are weaker than the individual components. (C)</p> Signup and view all the answers

What occurs at the maximum point in the vapor pressure curve for a solution with positive deviation?

<p>The total vapor pressure reaches its highest value. (A)</p> Signup and view all the answers

What characterizes non-ideal solutions in relation to Raoult’s law?

<p>Some components show positive deviation from Raoult’s law. (B)</p> Signup and view all the answers

What happens to the enthalpy change (Δmixing H) in non-ideal solutions?

<p>It can vary and is not equal to zero. (B)</p> Signup and view all the answers

In non-ideal solutions with positive deviation from Raoult’s law, what primarily influences the vapor pressure of the components?

<p>Weaker A-B interactions compared to A-A and B-B interactions. (B)</p> Signup and view all the answers

What is the volume change (Δmixing V) observed in non-ideal solutions?

<p>It is not equal to zero. (B)</p> Signup and view all the answers

In ideal solutions, how do components behave in terms of Raoult's law?

<p>They obey Raoult’s law at all concentrations and temperatures. (D)</p> Signup and view all the answers

Which statement is true about non-ideal solutions?

<p>They may show both positive and negative deviations from ideal behavior. (A)</p> Signup and view all the answers

What is the primary reason that non-ideal solutions deviate from ideal behavior?

<p>Interactions between components differ from those in pure components. (B)</p> Signup and view all the answers

Which of the following indicates a non-ideal solution under the provided conditions?

<p>Partial vapor pressures of components differ from Raoult’s law expectations. (A)</p> Signup and view all the answers

What is the relationship between the total pressure of a solution and its components according to Raoult's law?

<p>Total pressure is equal to the sum of partial pressures of each component (B)</p> Signup and view all the answers

What is a key characteristic of ideal solutions regarding heat change?

<p>The heat change during mixing is zero (A)</p> Signup and view all the answers

Which of the following pairs is classified as an example of an ideal solution?

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

In ideal solutions, how does the volume change on mixing relate to the individual volumes of the components?

<p>The total volume is exactly the sum of the components (C)</p> Signup and view all the answers

How do the vapour pressures in non-ideal solutions compare to those predicted by Raoult's law?

<p>They can be either higher or lower than predicted (B)</p> Signup and view all the answers

According to Dalton’s law of partial pressures, how is the partial pressure of a component in a vapour phase calculated?

<p>By multiplying the mole fraction by the total pressure (A)</p> Signup and view all the answers

What happens to the mole fraction of a component in the vapour phase when its partial vapour pressure increases?

<p>It increases if the total pressure is constant (A)</p> Signup and view all the answers

What is the main characteristic of azeotropic mixtures during distillation?

<p>They distill over as if they were pure liquids. (B)</p> Signup and view all the answers

Ethanol and water form a minimum boiling azeotrope at which composition?

<p>x(H2O) = 0.056 and x(C2H5OH) = 0.944 (B)</p> Signup and view all the answers

What happens to the total vapour pressure of solutions showing negative deviations from Raoult's law?

<p>It becomes less than the ideal solution. (C)</p> Signup and view all the answers

What defines maximum boiling azeotropes in terms of their boiling points?

<p>They boil at a composition with the highest boiling point. (C)</p> Signup and view all the answers

At what temperature does the minimum boiling azeotrope of ethanol and water boil?

<p>351 K (D)</p> Signup and view all the answers

At what composition does the maximum boiling azeotrope of hydrochloric acid and water occur?

<p>x(H2O) = 0.889 and x(HCl) = 0.111 (B)</p> Signup and view all the answers

What is the effect of fractional distillation on mixtures close to an azeotropic composition?

<p>It results in one pure component and an azeotropic mixture. (A)</p> Signup and view all the answers

What distinguishes minimum boiling azeotropes from maximum boiling azeotropes?

<p>Minimum boiling azeotropes boil at lower temperatures than their components. (D)</p> Signup and view all the answers

What happens to the observed molar mass when a solute dissociates in solution?

<p>It is less than the theoretical value (C)</p> Signup and view all the answers

How does KCl dissociate in solution and how many moles of particles does it produce?

<p>KCl dissociates to form 1 mol of K+ and 1 mol of Cl– ions, producing 2 mol of particles (A)</p> Signup and view all the answers

What is the Van’t Hoff factor 'i' for a solute that does not undergo dissociation or association?

<p>Equal to 1 (C)</p> Signup and view all the answers

Which of the following equations correctly relates the elevation in boiling point to the Van’t Hoff factor?

<p>Δ Tb = i Kb m (C)</p> Signup and view all the answers

What is the relationship between the observed colligative property and the normal colligative property in terms of the Van’t Hoff factor?

<p>i = Observed colligative property / Normal colligative property (D)</p> Signup and view all the answers

If the degree of dissociation is defined as the fraction of substance that dissociates, how is it mathematically represented?

<p>Degree of dissociation = No. of moles of substance dissociated / Total number of moles of the substance taken (A)</p> Signup and view all the answers

What is the expected increase in the boiling point when dissolving 1 mol of KCl in 1 kg of water, using the provided Kb value?

<p>1.04 K (A)</p> Signup and view all the answers

In which scenario would the Van’t Hoff factor be greater than 1?

<p>When a solute dissociates into more ions (B)</p> Signup and view all the answers

Flashcards

Non-ideal solution

A solution where the interactions between components differ from those in the pure components. This leads to deviations from Raoult's law.

Ideal solution

A solution where the interactions between components are similar to those in the pure components. This results in adherence to Raoult's law.

Negative deviation from Raoult's law

A solution where the vapor pressure of each component is lower than predicted by Raoult's law. This occurs when the interactions between components are stronger than the interactions between like molecules.

Positive deviation from Raoult's law

A solution where the vapor pressure of each component is higher than predicted by Raoult's law. This occurs when the interactions between components are weaker than the interactions between like molecules.

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Enthalpy of mixing (ΔmixingH)

The change in enthalpy when components are mixed to form a solution.

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Volume of mixing (ΔmixingV)

The change in volume when components are mixed to form a solution.

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Raoult's law

The partial vapor pressure of a component in a solution is directly proportional to its mole fraction and the vapor pressure of the pure component. This is a key characteristic of ideal solutions.

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Binary solution

A solution formed by two components.

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Azeotrope (or Azeotropic Mixture)

A liquid mixture that boils at a constant temperature and has a fixed composition. This means that it distills over as if it were a single pure substance.

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Minimum Boiling Azeotrope

An azeotrope with a boiling point lower than either of its pure components. These solutions show positive deviations from Raoult's law.

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Ethanol and Water Azeotrope

An example of a minimum boiling azeotrope. Its boiling point is lower than that of pure ethanol or pure water.

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Maximum Boiling Azeotrope

Azeotropes that have a boiling point higher than any of their pure components. These solutions show negative deviations from Raoult's law.

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Hydrochloric Acid and Water Azeotrope

An example of a maximum boiling azeotrope. Its boiling point is higher than either pure hydrochloric acid or pure water.

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Maximum Boiling Point

The boiling point of a solution at a specific composition is higher than that of either of the pure components.

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Negative Volume Change on Mixing (ΔmixingV)

The process of mixing two components where the resulting solution's volume is smaller than the sum of the individual component volumes.

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Negative Enthalpy Change on Mixing (ΔmixingH)

The change in enthalpy (heat energy) when two components are mixed, where negative values indicate energy release, making the mixing process exothermic.

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Escaping Tendency

The tendency of a substance to escape into the vapor phase, measured by its vapor pressure.

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Stronger A-B Interactions

The phenomenon where molecules of different components in a solution exhibit stronger attractive forces to each other than they do to their own kind.

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Azeotrope

A special case of positive deviation where the total vapor pressure of the solution reaches a maximum value for a specific composition, resulting in a minimum boiling point.

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Heat Change on Mixing (ΔmixingH)

The change in heat energy when two components are mixed to form a solution. In ideal solutions, there is no change in heat energy upon mixing.

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Volume Change on Mixing (ΔmixingV)

The change in volume when two components are mixed to form a solution. In ideal solutions, there is no change in volume upon mixing.

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Partial Vapor Pressure

The pressure exerted by a component of a solution when it is in equilibrium with its vapor phase.

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Dalton's Law of Partial Pressures

The total pressure of a solution is equal to the sum of the partial pressures of its individual components.

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Mole Fraction of a Component in Vapor Phase

The ratio of the partial pressure of a component in the vapor phase to the total pressure of the solution. This indicates the relative amount of that component in the vapor phase.

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Degree of Dissociation

The fraction of solute molecules that dissociate into ions in a solution. It is represented by the symbol α.

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Van't Hoff Factor (i)

The ratio of the observed number of moles of solute to the normal number of moles of solute. It tells us how many particles are actually present in solution compared to the theoretical number.

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Degree of Association

The fraction of solute molecules that associate to form larger molecules in a solution. It is represented by the symbol α.

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Number of Ions (n)

The number of particles that a solute dissociates into when dissolved in a solution. For example, NaCl dissociates into two ions (Na+ and Cl-) so n = 2.

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Van't Hoff Factor (i) and Molar Mass

The ratio of the normal molar mass to the observed molar mass of a solute. It is used to calculate the degree of dissociation or association.

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Colligative Property

A property of a solution that depends on the concentration of solute particles, not their identity.

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Relative Lowering of Vapor Pressure

The phenomenon where solute particles in a solution lower the vapor pressure of the solvent.

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Elevation in Boiling Point (ΔTb)

The increase in boiling point of a solvent when a non-volatile solute is added.

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Depression in Freezing Point (ΔTf)

The decrease in freezing point of a solvent when a non-volatile solute is added.

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Osmotic Pressure (Ï€)

The pressure that must be applied to a solution to prevent the inward flow of solvent across a semipermeable membrane.

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Association

The process where solute molecules in a solution combine to form larger molecules.

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Study Notes

Introduction to Solutions

  • Solutions are homogeneous mixtures of two or more components.
  • A solvent is the component in a solution with the same physical state as the solution and present in the greatest amount.
  • A solute is the component of a solution that is not the solvent.

Types of Solutions

  • Solutions can be composed of gases, liquids, or solids as solvents and solutes.
  • Binary solutions are composed of two substances.
  • Examples include gas mixtures (like oxygen and nitrogen), liquid solutions (like ethanol in water), and solid solutions (like copper dissolved in gold).

Some Important Definitions

  • A mixture is formed when two or more non-reacting substances are combined.
  • A heterogeneous mixture consists of distinct phases with properties simply adding up.
  • A homogeneous mixture forms a single homogenous phase.

Expressing the Strength of Solution

  • Concentration refers to the amount of solute dissolved per unit volume of solution.
  • Common expressions include mass percent, volume percent, molality, molarity, and mole fraction.
  • Mass percent (mass of solute / total mass of solution) x 100
  • Volume percent (volume of solute / total volume of solution) x 100
  • Molality (moles of solute/ mass of solvent (kg))
  • Molarity (moles of solute / volume of solution (L))
  • Mole fraction (moles of solute / total moles of solution)

Solubility of a Solid in a Liquid

  • Polar solutes dissolve in polar solvents, while nonpolar solutes dissolve in nonpolar solvents.
  • Dissolution is the process where solute dissolves and its concentration increases.
  • Crystallization is where solute particles separate out.
  • A saturated solution holds the maximum amount of solute at a constant temperature and pressure.
  • Unsaturated solutions hold less solute than the maximum amount.

Solubility of Gases in Liquids

  • The solubility of a gas in a liquid decreases as the temperature increases.
  • The solubility of a gas in a liquid increases as the pressure increases.
  • Henry's law states that the solubility of a gas in a liquid is directly proportional to the pressure of the gas.
  • This law applies at a constant temperature.

Vapour Pressure of Solution

  • Vapor pressure is the pressure exerted by vapor on the liquid's surface when equilibrium exists between vapor and liquid.
  • The nature of the liquid affects vapor pressure. Liquids with stronger intermolecular forces have lower vapor pressures.
  • Temperature affects vapor pressure. Higher temperatures lead to higher vapor pressures.

Ideal and Non-Ideal Solutions

  • Ideal solutions obey Raoult's law, which states that the partial pressure of a component in a solution is directly proportional to the component's mole fraction.
  • In ideal solutions, the enthalpy and volume changes upon mixing are zero.
  • Non-ideal solutions do not obey Raoult's law.

Colligative Properties

  • Colligative properties (like vapor pressure lowering, boiling-point elevation, freezing-point depression, and osmotic pressure) are solution properties directly related to the solute concentration (not the nature of the solute).

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Description

Explore the fundamentals of solutions, including the roles of solvents and solutes, and the types of solutions. This quiz covers essential definitions and concepts such as concentration and the difference between homogeneous and heterogeneous mixtures.

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