Separations Involving Phase Changes
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Questions and Answers

What is the main purpose of vacuum distillation?

  • To increase the temperature during distillation
  • To create an azeotrope during the process
  • To allow the distillation of compounds at lower temperatures (correct)
  • To separate compounds with similar boiling points

    • What is the initial step in the lyophilization process?

  • Subject the sample to high pressure
  • Freeze the sample (correct)
  • Apply heat to the sample
  • Immerse the sample in liquid nitrogen

    • Under what conditions does water sublime during the lyophilization process?

  • At room temperature and atmospheric pressure
  • At temperatures above 0 oC and pressures above 4.57 torr
  • At any temperature and pressure below 100 Pa
  • At temperatures below 0 oC and pressures below 4.57 torr (correct)

    • Which of the following is true regarding lyophilization?

    <p>It is suitable for heat-sensitive materials</p> Signup and view all the answers

    What distinguishes vacuum distillation from regular distillation?

    <p>It operates below atmospheric pressure</p> Signup and view all the answers

    What is the primary purpose of volatilization?

    <p>To convert solid or liquid to gas</p> Signup and view all the answers

    Which method is NOT used to achieve volatilization?

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

    In simple distillation, what is the main process that occurs after vaporization?

    <p>Condensing the vapor into a liquid</p> Signup and view all the answers

    What is the use of a fractionating column in fractional distillation?

    <p>To increase surface area for repeated vaporization</p> Signup and view all the answers

    What is the result of adding a strong acid to a solid weak acid like CaCO3?

    <p>Evolution of gaseous CO2</p> Signup and view all the answers

    How is moisture content determined from the given weights of a sample?

    <p>By calculating the difference in weight before and after drying</p> Signup and view all the answers

    What is one characteristic of vacuum distillation?

    <p>Reduces boiling points by creating a vacuum</p> Signup and view all the answers

    Which of the following processes would be the best option for separating two volatile liquids with similar boiling points?

    <p>Fractional distillation</p> Signup and view all the answers

    Study Notes

    Volatilization

    • Volatilization involves converting solids or liquids into gases through various methods.
    • Methods include heating (e.g., NH4NO3 to N2 and H2O), displacing weaker acids/bases with stronger ones (e.g., CaCO3 with HCl), oxidation (e.g., burning sulfides to SO2), and reduction to form hydrides (e.g., AsH3).

    Moisture Determination

    • Example calculation for moisture percentage:
      • Empty aluminum dish: 1.9593 g
      • Dish + sample: 2.8410 g
      • After constant weight: 2.7555 g
      • Calculate % moisture using these weights.

    Distillation

    • Distillation separates vapor from a liquid through heating and subsequent condensation.

    Simple Distillation

    • Involves heating a liquid, vaporizing it, and cooling the vapor to collect as liquid.
    • Example: Separating water from sea salts.

    Fractional Distillation

    • Utilized for separating miscible, volatile liquids with close boiling points.
    • Requires a fractionating column for repeated evaporation and condensation.

    Vacuum Distillation

    • Reduces atmospheric pressure to decrease heating temperatures.
    • Prevents polymerization and decomposition of heat-sensitive compounds.

    Lyophilization (Freeze-Drying)

    • Sublimation process removes water from frozen samples without passing through a liquid phase.
    • Ideal for heat-sensitive materials that could be damaged by conventional drying.
    • Process: freeze sample, apply vacuum for sublimation to occur without melting.
    • Water can sublime below 0 °C and pressures under 4.57 torr, commercially classified if operating below 100 Pa (0.75 torr).

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    Separations Involving Phase Changes PDF

    Description

    This quiz explores the various methods of separations involving phase changes, focusing on volatilization, distillation, and lyophilization. Understand the principles and applications of these techniques as discussed by lecturer Chong Arechkang, MSc.

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