Distillation
Distillation
Separation of compounds based on differences in their boiling points
If one compound is substantially more volatile than the other, what process is used?
Simple distillation
Volatile
high vapor pressure, low boiling point
Boiling point characteristics
Bubbles of vapor produced throughout liquid
Basis of distillation?
Change in composition that accompanies the vaporization process
When is the concentration of the more volatile compound increased during fraction distillation. Explain.
Concentration of more volatile compound increases as vapors move up column. Each condensation-revaporization phase increases concentration of more volatile compound.
Where are the pot produced vapors cooled?
Condenser
Function of fractioning column?
Contains glass beads and metal sponge. Vapor condenses on cooler surfaces, reheated by rising vapors, and re-vaporizes.
If the boiling points of two compounds differ by less than 40°C, what process is used?
Fractional distillation
Each condensation-revaporization cycle results in what?
Increase in concentration of more volatile compound.
Why does the rate of vapor produced increase in the case of which heating rate is increased during boiling?
Liquid particle absorb more energy, overcome intermolecular interactions, and enter gaseous state.
Distillation rate must not be conduced too rapidly. Why?
Liquid-vapor equilibria will not be established. Poor separation.
Fractional distillation has the effect of?
Many simple distillations
What is evaporation?
Molecules at liquid surface gain sufficient energy to enter the gaseous state
Where are compounds heated in distillation apparatus?
Pot
Equilibrium vapor pressure
Pressure exerted by gaseous particles at liquid-gas equilibrium on walls of container
Why must the fractioning column be positioned vertically?
Promote percolation
Where is the condensed liquid collected?
Receiver
Distillation is useful for what?
Removing a volatile solvent from a nonvolatile product; separate a volatile product from nonvolatile impurities; separate two or more volatile products that have sufficiently different boiling points
Mixture of two volatile compounds heated, what is the total vapor pressure?
Sum of the vapor pressures of each compound
Boiling point
Temperature at which vapor pressure is equal to external pressure exerted on liquid
When does evaporation occur?
Temperature below boiling point
Homogeneous mixture will boil at what?
Temperature between the boiling points of pure compounds
When heating rate is increased during boiling, what occurs?
Temperature does not change. Rate at which vapor is produced increases.
How and why do you position the thermometer head?
Top of thermometer should be with side arm on distilling head. Ensures head is immersed in vapor.
Distillate has the same composition as?
The vapor of which it is produced
Each condensation-revaporization is called what?
Theoretical plate
When vapor is produced from a liquid mixture, describe the vapor composition.
Vapor composition is different from that of liquid mixture. Contains a larger percent of the more volatile compound.
Define: Miscible
When two compounds form a homogeneous mixture