Subject:
Separation of Liquids by Simple Distillation and Analysis by Gas Chromatography

Methods and Background: Chromatography is a normal experimental method that used for separating a mixture solution with two or more compounds. Generally, the major function is a mixture component that will distribute unequally between phases. Those phases do not present a homogenous mixture and they are mobile phase and stationary phase. Gas chromatography is different with other kinds of chromatography that a gas is the mobile phase and a liquid is the stationary phase. In this laboratory, gas chromatography was detected and verified the purity of the distillation of a 1:1 ethyl acetate and butyl acetate mixture solution. Separated the mixture was based on the meaning of gas chromatography. The 1:1 ethyl acetate and butyl acetate mixture was divided through simple distillation – the three fractions were collected during the laboratory. The simple distillation separated pure substances from nonvolatile substance. Based on different compounds in mixture have different boiling points, the simple distillation also was used to separate components of the mixture. In this experiment, the mixture was composed by ethyl acetate and butyl acetate. Ethyl acetate has a boiling point of 77 Celsius. Butyl acetate has a boiling point of 126 Celsius. Therefore, the 1:1 ethyl acetate and butyl acetate mixture should separate successfully through distillation as well as two individual components have approximately 50 Celsius. When the vapor pressure of given sample equals to the total pressure, the boiling point is reached. Since the rate of evaporation goes up, we can see the bubbling in the liquid in which means that the substance will be vaporized. According to Dalton’s law of partial pressures that the total pressure is the sum of the individual pressure, it means that P­air = P­sample + Pair. If the temperature decreases, the vaporized solution would return to its original liquid form. In simple distillation, a liquid mixture is heated. The substance with the lower boiling point vaporizes, and then it is allowed to condensate back to a liquid form into a cool graduated cylinder. In this laboratory, ethyl acetate has a lower boiling point of 77 Celsius in the mixture. Therefore, ethyl acetate will distill out first. As the temperature rises and achieves 120 Celsius, butyl acetate will start to distill out. When the experiment ends, this 1:1 (v/v) ethyl acetate & butyl acetate mixture has been vaporized completely. Also, it will be collected as three fractions. A gas-liquid chromatography machine will be used to check the purity of the three fractions. In the methods of chromatography, the mobile phase is a gas and the stationary phase is a liquid. In the particular machine of chromatography, the mobile phase was a helium gas and the stationary phase was a polar liquid. Separated samples were based on their affinities of the mobile and stationary phases. If a sample is more polar, it would tend toward a high affinity and have a longer retention time. In the laboratory, butyl acetate has a longer retention time.

Procedure:
Distillation
1. Added 30ml 1:1 (v/v) mixture of ethyl acetate and butyl acetate into a round bottom flask. Also, added one boiling stone in the mixture.
2. Turned on the faucet to ensure a flow of water into the condenser.
3. Heated the solution gradually until distillation proceeded at approximately one drop per second.
4. Recorded the head temperature every milliliter of distillate.
5. Collected three fractions. The first fraction was collected until the temperature reached 87 Celsius. The second fraction was collected until the temperature achieved 120 Celsius. The third fraction was collected until the temperature reached closed to the boiling point of butyl acetate.
Gas-Liquid Chromatography
1. On a COW-MAC 400 GC with a carbowax column, isothermal gas-liquid