Lab Report: Fractional Distillation And Gas Chromatography

Fractional Distillation and Gas Chromatography (Investigative)
Kevin Dural
The University of Texas at Austin
Fractional Distillation and Gas Chromatography (Investigative)
Data and Results
All data and results are attached. Included are carbon copies of written data and printed gas chromatography data.
Discussion
The purpose of this experiment was to identify two unknowns and their ratios in a given mixture. The identities of the unknowns were two of either acetone, methanol, hexane, cyclohexane, heptane, toluene, or ethyl benzene.
Distillation
Distillation is used to remove impurities from a mixture – one component of which must be a liquid. Boiling points are utilized in determining the identity of the unknowns. Types of distillation include

Dalton’s law, as described before, states that the sum of the partial pressures of each component in a solution – two or more volatile compounds – is equal to the total pressure. As this now includes more than one compound when separating volatile substances from each other, fractional distillation must be used. Fractional distillation, which can be viewed as a series of simple distillations, is a method used to separate volatile impurities from its solvent. The main difference is that a column is introduced between distillation flask and head to separate the liquids from each other. This column – of a large surface area with glass or ceramic – provides ample contact between the vapor and liquid phases. A temperature gradient is formed because the head of the system is now further from the flask. Factors that affect the temperature gradient include the rate of heating and vapor removal from the system’s stillhead. Upon heating, the vapor of compound A rises, reaching a distance at which it no longer has enough energy to maintain its gaseous form; at this point, the molecules re-enter the liquid state. This process of rising up, condensation, and revaporization eventually results in vapor comprising 100% of substance A. This process is then repeated at the boiling point of substance B. The efficiency of this process is reflected by the reflux ratio, which reveals how many condensate drops reenter the stillpot for every distillate drop

The data cannot be used solely for identification of the unknowns because Raoult’s law can only be applied to ideal solutions where the intermolecular forces between like and unlike molecules are considered equivalent. This is definitely not the case in the laboratory, so the presence of impurities and their resultant intermolecular interactions may mean that the boiling point of what is considered compound A is not equivalent to the literature boiling point value of a compound. As a result, data from the GC chromatograms must also be