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Lecture 9

CHEM 235 Lecture Notes - Lecture 9: Fractional Distillation, Azeotrope, Potentiometer


Department
Chemistry
Course Code
CHEM 235
Professor
Dana Zendrowski
Lecture
9

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NOTES:
Distillation: (1) heating a substance until it vaporizes, (2) condensing the resulting vapours
by cooling, (3) collect condensate (distillate) in a separate vessel called receiver
Similar to refluxing condensate is returned to original vessel
Purposes:
- Separating a mixture when the components of the mixture have different BP
- Principle method used for purifying a liquid
Conditions:
- at least one component in the mixture must be volatile (nonvolatile solids would be
left behind in distillation flask)
- wide separation between BP (50˚C or more) if separating two or more volatile liquids
- components must not form an azeotrope (intermolecular interactions between
components of mixture so that liquid distills at constant temp/composition even
though components have different BPs e.g. ethanol and water @ 95% and 5%)
Boiling point: when total vapour pressure = atmospheric pressure (constant for pure
substance)
Criteria of purity for a liquid:
(1) BP of neat liquid
(2) Refractive index (R.I.) of the liquid
- the measure of change in light path (refraction) as light passes at an angle from one
medium to another (i.e. air to liquid)
- unique property of each medium
- physical constant depend on wavelength of light and temperature
EQUIPMENT:
thermometer takeoff adapter + elastic band
400 mL beaker 10 mL graduated cylinder
2 - small test tubes with corks 25 mL graduated cylinder
100 mL RB flasks thermowell (heating mantle)
stillhead adapter rheostat
West condenser iron ring + wooden square
2 pieces rubber tubing refractometer
CHEMICAL HAZARDS AND WASTE DISPOSAL
Glycerol
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