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








Goals of Gas Chromatography




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




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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