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Distillation & Refractive Index
Chem 51LA
Boiling Point & Distillation
• Distillation: Separation method for liquid compounds based on differences in _____ _____
• Boiling point: the temperature at which the _____________ of a liquid is equal to the _____________.
Vapor Pressure & Boiling Point
• high vapor pressure = low boiling point
vapor pressure
applied pressure
Factors That Affect Boiling Point of a Substance
• Molecular weight: higher molecular weight = higher boiling point
methane propane hexane
MW 16 44 86
BP (°C) -164 -42 69
Factors That Affect Boiling Point of a Substance
• Hydrogen Bonding CH3CH2CH3 CH3CH2OH
MW 44 46
BP (°C) -42 78
• Dipole-Dipole Interactions CH3CH2CH3 CH3OCH3 CH3CH=O
MW 44 44 44
BP (°C) -42 -24 21
Temperature/Composition Diagram
• Composition of vapor above a mixture depends on mixture composition.
• Raoult’s Law
• Dalton’s Law
Simple Distillation Setup
Setting Up Water Circulation
• Study the Recirculating Pump SOP on class website BEFORE your lab section!
Simple Distillation Curve
• Initial distillate collected above the boiling point of pentane.
• Final distillate never reaches boiling point of hexane.
Simple Distillation Curve
30
35
40
45
50
55
60
65
70
0 10 20 30 40 50
Volume of Distillate
Dis
till
ati
on
Tem
peratu
re
Fractional Distillation Setup
• Fractionating column allows vapor to condense and vaporize multiple times.
Fractional Distillation Curve
• Initial distillate will be very close to boiling point of pentane.
• Final distillate will be very close to boiling point of hexane.
Refractive Index
• The refractive index is the ratio of refraction of _______ over refraction of _________ _______.
• Each liquid has a different refractive index.
• Light is bent (refracted) when it passes through a liquid.
Measuring Refractive Index
• Be VERY careful with the prism surface! Blot gently with kimwipe to
clean. Don’t touch the surface with a
pipette! • Align the fields with the
crosshairs. • Make sure the fields have
no color.
Experimental Details
Experiment Notes
• Experiment is done in groups of 4. One pair will do simple distillation. One pair will do fractional distillation. There is only ONE unknown per group of 4. You will need to
split it. • Placement of thermometer is CRUCIAL! • Collect temp. data every .5 mL. • Plot your graph while collecting data. • Do RI of sample compounds and distillate from fractional
distillation.