UCLA Chemistry 20L Flashcard

 

 

 

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

;

Phexane + Ptoluene = 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

 

PA = P0A * XA

 

 

 

 

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 = ;bc

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