Simple Distillation

Separating liquids boiling BELOW 150°C

Difference in boiling point should be at least 25°C

We used this to separate ethyl acetate from toluene

Vacuum Distillation

Separating liquid mixture ABOVE 150°C at 1 atm

Fractional Distillation

Difference in boiling point is less that 25°C

Steam Distillation

Used mainly to isolate tars and oil mixtures

Normal Boiling Point

Temperature at which the vapor pressure of the liquid is exactly equal to 1 atm

Dalton's Law of Partial Pressures

The total pressure of the system equals the sum of the partial vapor pressure of each component

P_hexane + P_toluene = 760 torr

Raoult's Law

The partial vapor pressure of a component in the solution is equal to the PURE vapor pressure of A times its mole fraction

P_A = P⁰_A * X_A

Relationship between vapor pressure and boiling point

High vapor pressure normally means low boiling point

Low vapor pressure normally means high boiling point

Retention Time

The time between injection of the liquid mixture and the output of the GC signals from the GC detector

Mobile Phase

The carrying gas in gas chromatography. Most common carrying gas is Helium.

Stationary Phase

The gas chromatography column. The inside of the column usually consists of a HIGH BOILING POINT liquid coated on a solid support. The entire column is then sealed inside a coiled metal tube.

London Dispersion Forces

- Weakest intermolecular force

- Not a permanent dipole

- It is not always true that low boiling point implies London forces

Dipole Forces

Example: Electronegativity

C = O

  δ+      δ -

Hydrogen Bonding

H - O

H - N

H - F

Ionic Forces

NaCl

Goals of Gas Chromatography

Separation

Quantification (%)

Identification (retention time)

Speed of the GC recorder

4.0 cm/min

Area of individual signal on GC chromatogram

Width at half height x height (unit in cm²)

% Composition for each individual component in GC

100% x (Individual Area / Total Area)

The 5% Rule (acid-base)

Y/(0.1000) x 100% ≤ 5%

At half equivalence point . . .

[HA] = [A^-]

moles of weak acid = moles of conjugate base

pH = pKa

At equivalence point . . .

[HA] = [OH^-]

moles of weak acid = moles of strong base

Composition of Buffer Solutions

Weak acid and its conjugate base

OR

Weak base with its conjugate acid

Limits of the Henderson-Hasselbalch Equation

- Ka for the weak acid must be within the limits oft he approximation (≤10^-5)

- Applies only to buffer solutions

Range of Visible Light

380 nm - 750 nm

Beer's Law

A = εbc