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Sublimation

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Sublimation

Sublimation will eventually cause frozen objects to dry

How did the early settlers do their laundry in the winter?

Of course, they could wash the clothes inside, but where to dry them?  There were no dryers available, so the clothes had to be hung up to dry.  In the winter, you would expect that ice would form on the clothes, but that didn’t happen.  Even in freezing weather, the water might freeze initially, but would eventually go off as a vapor – from solid ice directly to the gas stage.  There are still families today who have to rely on this cumbersome process to get their laundry done.

Sublimation 

Vapor Pressure of a Solid

"Sublimation" reviews the vapor pressure of a liquid and its dependence upon temperatureSolids also have a vapor pressure, though it is generally much less than that of a liquid.  A snow bank will gradually disappear even if the temperature stays below 0°C.  The snow does not melt, but instead passes directly from the solid state to the vapor state.  Sublimation is the change of state from a solid to a gas without passing through the liquid state.

"Dry ice," or solid carbon dioxide, is a substance that sublimes at atmospheric pressures.  Dry ice is very cold (−78°C) and so is used as a coolant for goods such as ice cream that must remain frozen during shipment.  Because the dry ice sublimes rather than melting, there is no liquid mess associated with its change of state as the dry ice warms. As you may have seen in demonstrations, dry ice merely transforms from a solid to a cold, steamy looking gas.  Ferrocene (an iron-containing compound) is usually purified by sublimation by gentle warming at atmospheric pressure.  In the Figure below , you can see the reddish ferrocene crystals deposited on the outside of that tube.  Deposition is the change of state from a gas to a solid.

Ferrocene purified by sublimation.

Summary

  • Sublimation is the change of state from a solid to a gas without passing through the liquid state.
  • Deposition is the change of state from a gas to a solid.
  • Carbon dioxide is an example of a material that easily undergoes sublimation.

Practice

Questions

Use the link below to answer the following questions:

http://www.newworldencyclopedia.org/entry/Sublimation_%28chemistry%29

  1. How is sublimation used by chemists?
  2. Describe the process of purification by sublimation.
  3. What is lyophilization?

Review

Questions

  1. Define sublimation.
  2. How is ferrocene purified?
  3. Name a substance which undergoes sublimation.

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