Raoult's Law and Freezing Point Depression
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Questions and Answers

What is the molarity of the NaOH solution calculated from 5g dissolved in 450 mL of solution?

  • 0.500 M
  • 0.350 M
  • 0.125 M
  • 0.278 M (correct)

    • Which of the following describes molality correctly?

  • It varies with temperature, unlike molarity.
  • It is defined as moles of solute per kilogram of solvent. (correct)
  • It is defined as moles of solute per liter of solution.
  • It refers to the mass of solute divided by the volume of solvent.

    • Why is molarity considered a function of temperature?

  • Volume varies with temperature while mass does not. (correct)
  • It is calculated based on the weight of the solvent.
  • Volume is not affected by temperature.
  • The mass remains constant regardless of temperature.

    • What is the formula used to calculate molality?

    <p>Molality (m) = Moles of solute / Mass of solvent in kg</p> Signup and view all the answers

    How many moles of KCl are present in 1.00 mol kg (or 1.00 m) solution of KCl?

    <p>1.00 mole</p> Signup and view all the answers

    What happens to the vapor pressure of a solvent when a non-volatile solid is added?

    <p>It decreases.</p> Signup and view all the answers

    How is the depression in freezing point ( extDelta T_f) related to the molality (m) of the solution?

    <pre><code>extDelta T_f = K_f imes m </code></pre> Signup and view all the answers

    What does the constant K_f represent in the context of freezing point depression?

    <p>Freezing Point Depression Constant</p> Signup and view all the answers

    What is the relationship between the initial freezing point of the pure solvent (Tf0) and the freezing point when a solute is dissolved (Tf)?

    <p>Tf is less than Tf0.</p> Signup and view all the answers

    If 5 grams of a solute with molar mass M2 are dissolved in 100 grams of solvent, what is necessary to calculate the molality of the solution?

    <p>Both the mass of the solute and its molar mass.</p> Signup and view all the answers

    What is defined as the difference between the freezing point of pure solvent and that of the solution?

    <p>Depression in freezing point ( extDelta T_f)</p> Signup and view all the answers

    What is the unit of the Freezing Point Depression Constant (K_f)?

    <p>K·kg·mol^{-1}</p> Signup and view all the answers

    When a solute is added to a solvent, what physical property primarily changes?

    <p>The freezing point of the solvent</p> Signup and view all the answers

    What happens during the process of dissolution?

    <p>Some solute dissolves and its concentration increases.</p> Signup and view all the answers

    What characterizes a saturated solution?

    <p>It is in dynamic equilibrium with undissolved solute.</p> Signup and view all the answers

    How does temperature affect the solubility of a solid in a liquid?

    <p>Generally increases solubility for endothermic dissolution.</p> Signup and view all the answers

    Which of the following best describes dynamic equilibrium in a solution?

    <p>The rate of dissolution equals the rate of crystallisation.</p> Signup and view all the answers

    What is an unsaturated solution?

    <p>A solution that can still dissolve more solute at the same temperature.</p> Signup and view all the answers

    According to Le Chatelier's Principle, what occurs if the dissolution process is exothermic?

    <p>Solubility should decrease with an increase in temperature.</p> Signup and view all the answers

    What defines solubility in a solution?

    <p>It is the maximum amount of solute that can be dissolved in a given solvent.</p> Signup and view all the answers

    Which of the following factors does NOT affect the solubility of a substance?

    <p>The concentration of solute already in solution.</p> Signup and view all the answers

    What does Raoult's law state about the partial vapor pressure of each component in a solution?

    <p>It is directly proportional to its mole fraction.</p> Signup and view all the answers

    In the equation for total pressure, which expression correctly represents the contribution of the two components?

    <p>ptotal = p1 + p2</p> Signup and view all the answers

    What do the symbols p10 and p20 represent in the equations?

    <p>The vapor pressures of the pure components at the same temperature.</p> Signup and view all the answers

    According to Dalton’s law of partial pressures, what is the relationship between the partial pressures and total pressure?

    <p>Total pressure is equal to the sum of the partial pressures.</p> Signup and view all the answers

    In the equations provided, how is the mole fraction x2 related to the two components in the solution?

    <p>It is the remaining fraction when x1 is subtracted from 1.</p> Signup and view all the answers

    In the context of the equations given, what does the expression (p20 - p10) * x2 indicate?

    <p>The difference in vapor pressures between the two components multiplied by the mole fraction of component 2.</p> Signup and view all the answers

    From the equations, what can be inferred about the relationship between mole fractions and total pressure?

    <p>Total pressure increases with the mole fractions of components.</p> Signup and view all the answers

    In a solution made of two components, what does an increase in the mole fraction of component 1 (x1) imply?

    <p>A decrease in the mole fraction of component 2 (x2).</p> Signup and view all the answers

    What happens when pressure exceeding osmotic pressure is applied to seawater?

    <p>Pure water is squeezed out from the seawater through the membrane.</p> Signup and view all the answers

    What is the role of cellulose acetate in the reverse osmosis process?

    <p>It allows water to pass while blocking impurities and ions.</p> Signup and view all the answers

    Which of the following is true about the polymers used in reverse osmosis?

    <p>The polymer membranes can be made from cellulose acetate.</p> Signup and view all the answers

    What is the expected result when one mole of KCl is dissolved in water?

    <p>An increase in boiling point by 1.04 K is expected.</p> Signup and view all the answers

    What is the boiling point of water at a pressure of 750 mm Hg?

    <p>99.63°C</p> Signup and view all the answers

    To achieve boiling at 100°C, how much sucrose is required to be added to 500 g of water?

    <p>25 g</p> Signup and view all the answers

    What is the vapor pressure of pure water at 298 K?

    <p>23.8 mm Hg</p> Signup and view all the answers

    How much ascorbic acid is required to lower the melting point of 75 g of acetic acid by 1.5°C?

    <p>10 g</p> Signup and view all the answers

    Study Notes

    Raoult's Law

    • When a non-volatile solid is added to a solvent, its vapor pressure decreases.
    • This decrease in vapor pressure is proportional to the mole fraction of the solute.
    • The freezing point of the solvent also decreases.

    Freezing Point Depression

    • The decrease in freezing point (∆Tf) is the difference between the freezing point of the pure solvent (Tf0) and the freezing point of the solution (Tf).
    • ∆Tf is directly proportional to the molality (m) of the solution.
    • The proportionality constant is the Freezing Point Depression Constant or Cryoscopic Constant (Kf).

    Calculating Molality

    • Molality is defined as the number of moles of solute per kilogram of solvent: Molality (m) = Moles of solute / Mass of solvent in kg.

    Dissolution and Crystallisation

    • When a solid solute is added to a solvent, dissolution occurs, resulting in an increase in solute concentration.
    • Crystallisation occurs when solute particles in solution collide with solid solute particles and separate out.
    • Equilibrium is reached when the rates of dissolution and crystallisation are equal, resulting in a saturated solution.

    Solubility

    • Solubility is the maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature and pressure.
    • The solubility of a solid in a liquid is influenced by temperature and follows Le Chatelier's principle.
    • Endothermic processes result in increased solubility with increased temperature.
    • Exothermic processes result in decreased solubility with increased temperature.

    Raoult's Law for Volatile Liquids

    • Each component in a solution of volatile liquids has a partial vapor pressure directly proportional to its mole fraction in the solution.
    • This is represented by the equations p1 = p10 x1 and p2 = p20 x2.

    Total Vapor Pressure

    • The total vapor pressure (ptotal) over the solution is the sum of the partial vapor pressures of each component.
    • This is represented by the equation ptotal = p1o + (p20 - p10) x2.

    Reverse Osmosis

    • Reverse osmosis is a process where pressure is applied to a solution to force water molecules through a semi-permeable membrane leaving behind the solute.
    • This technique is used to desalinate water by removing impurities and ions.

    Abnormal Molar Masses

    • Ionic compounds dissociate into ions when dissolved in water.
    • This results in an increased number of particles in the solution and can affect properties like boiling point elevation.

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    Description

    This quiz covers the concepts of Raoult's Law and freezing point depression in solutions. It explores how the addition of a non-volatile solute affects vapor pressure, freezing point, and molality. Test your understanding of these important concepts in solution chemistry.

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