Distillation

Rate of heating

1-3 drops per second

simple vs fractional distillation

Simple = larger differences in BP (100C+) (less specific) Fractional = extra surface area with glass column BEFORE the condenser allows for multiple evaporation-condensation cycles - more surface area (glass beads) = more cycles

It is important for the distillation apparatus to be supported on its own so that:

The heat source can be lowered easily to reduce the heat in the event that the distillation is proceeding too quickly

theoretical plate

amt of surface area on which repeated condensation & vaporization occurs that has the effect on purity of a single simple distillation

When removing large amounts of volatile solvents from high boiling point liquids or solids it is common to do so by applying a vacuum with gentle heating (a rotary evaporator is a common piece of lab equipment that is designed for this purpose). What type of distillation is this?

simple distillation

When will boiling occur?

- boiling occurs when the *vapor pressure equals the applied pressure*

Do you expect steam distillation to be an effective method of separating tetrahydrofuran from water?

-No, tetrahydrofuran is miscible with water.

If collecting a boiling point for compound during distillation, what temperature should be recorded?

-The temperature plateau that is achieved once the vapors of the desired compound begin to pass into the cold-water condenser.

What is the purpose of a steam distillation?

-To distill high boiling point oils at a lower temperature without the use of vacuum -To separate volatile organic compounds from solids (e.g., plant leaves)

azeotropes

-a mixture of two liquids that has a constant boiling point and composition throughout distillation -there exists a *molar fraction where the vapor generated when boiling has the same composition as the liquid rendering the system static* -can't be further purified by distillation -*composition of ex/ ethanol & water

Boiling chisp

-allows for uniform heating & avoid bumping inside the liquid

Fractional distillation

-allows vapor to condense and then re-vaporize at multiple pts within the column -each cycle of condensation and vaporization produces a vapor that contains a larger % of the lowest BP liquid

Why is cold water put at the bottom of the condenser?

-cold water put at the bottom b/c going against gravity allows for effective cooling of the mixture -if cold water @ top, cold water immediately leaves & doesn't fill flask completely

What is distillation?

-conversion of a compound from the l phase to g phase, followed by condensation of the gas, leading to the isolation of a purer liquid compound -*separate liquids*

Fractionating column

-promotes the repeated cycling of the vaporization-condensation cycles -designed to inc surface area

purpose of simple distillation

-remove 1 volatile liquid from another less volatile liquid or nonvolatile substance -required when a liquid compound needs to be removed from a solvent (e.g. after an extraction) or as a purification process when the impurities and the product have significantly diff volatilities -effective w/ large diff (at least 50 deg diff)

How do you know the volume of the mixture in fractional distillation?

-take midpt of slope, draw line from center of curved slope then bring to x-axis

Vaporization-condensation cycle

fractional distillation

HETP

height equivalent theoretical plate -packed column HETP = 1.5 cm (steel wool/mesh) -vigreux column HETP = 10 cm

Theoretical plates

hypothetical zone or stage in which two phases, such as the liquid and vapor phases of a substance, establish an equilibrium with each other. Such equilibrium stages may also be referred to as an equilibrium stage or ideal stage -*used to describe the efficiency of a fractionating column & represent the # of cycles of vaporization/condensation* -If a column contains enough theoretical plates, it will be able to separate out two liquids to a high degree of purity