SIMPLE DISTILATION- lab report

 ORGANIC CHEMISTRY

SIMPLE DISTILATION

 

INTRODUCTION

 Distillation is an inexpensive and relatively simple technique used to purify liquids. Chemists often use this method to separate homogeneous solutions of two or more liquids. In industry, distillation is used to separate the economically important components of fossil fuels including natural gas, gasoline, kerosene, heating oil, and lubricants. In the food industry, distillation is used to concentrate the alcohol in wines and other beverages obtained from the natural fermentation of fruits and vegetables. Both of these economically important processes separate liquids, which do not interact with one another, by differences in their boiling points. In practice, liquids can be separated by simple or fractional distillation as discussed in Mohrig. In this experiment, you will be using two distillation methods to separate an alcohol from an organic solvent. Using either the blue or white glassware kits, you should separate the 60-mL unknown sample with both simple and fractional macro scale distillation.  You and a partner will be randomly assigned one unknown alcohol/solvent mixture to purify by both methods. On the following two pages the apparatus for each distillation is represented. After comparing the quality of the two methods by constructing a distillation curve and analyzing the purified liquids by gas chromatography (GC), you will identify the pure alcohol from boiling point data, refractive index (RI) and infrared spectra (IR).

figure;1

Distillation is a separation technique that takes advantage of the boiling point properties of mixtures. To perform distillation, a miscible mixture of two liquids with a significant difference in boiling points at least 20 °C is heated. As the solution heats up and reaches the bubble point of the more volatile component, some molecules of the more volatile component transition into the gas phase and travel upward into the condenser. The condenser is a glass tube with separate inner and outer sections. The vapor travels into the inner section of the condenser, where it is condensed to liquid by the cold water flowing in the outer section of the condenser. This condensed vapor is called the distillate, and it is collected in a graduated cylinder or test tube.

As the distillation progresses, the temperature needed to boil the solution increases as the more volatile component boils off earlier. Thus, the composition of the distillate changes over time. Early on in the distillation, the distillate is rich with the more volatile component; in the middle of the distillation, the distillate contains a mix of the two components; and at the end of the distillation, the distillate is rich with the less volatile component.

The vapor-liquid equilibrium diagram shows the change in both the composition of the liquid in the flask and the distillate over the course of the distillation. There are two curves on the plot; the bottom curve describes the boiling point of the liquid in the flask as it relates to its composition, while the top curve describes the temperature of the vapor as it relates to its composition. By extension, the top curve describes the composition of the distillate.

A published vapor-liquid equilibrium diagram from the literature can be used to identify the composition of the liquid and vapor at a given temperature during the experiment. This can help determine when to end the distillation to separate the two components.

 

 OBJECTIVES

1.     To determine the boiling point of liquid organic compound.

2.     Purifying liquids containing impurities.

3.     Separating two or more liquids having different boiling points.

 

 MATERIALS

 

Distillation apparatus

Thermometer

Retort stand

Bunsen burner

Boiling chips

Distilled water

KMNO₄

 

 METHODS

 

1.     Clean dry 250 ml round bottom flask was introduced 150ml of liquid containing colored impurities.

2.     One or two tiny boiling chips were added.

3.     The boiling flask was attached and make certain that all connection is tight.

4.     The liquid was heated and distilled slowly at a uniform rate 30-60 drops per minute.

5.     The temperature was recorded when the first drop of distillate collected from the condenser.

6.     The distill liquid was continue slowly.

7.     The distilling temperature was recorded at regular intervals during distillation.

8.     The distillation was discontinue when 2-5ml liquid remains in the flask.

9.     The average of the reading of the temperature was found.

10.  The volume of the pure liquid was measure and collected in the receiving flask.

 

QUESTIONS

1.     How do you know when distillation is complete?

 When the temperature of the thermometer starts to drop or when the distillation flak is empty.

2.     Where should the thermometer bulb in the distillation setup be placed and why?

 The bulb part of the thermometer is positioned near the side arm of the Y adaptor so that it monitors the temperature of the vapors. If it is too low, it will be too close to the boiling liquid and will read higher than the true vapor temperature.

 

3.     Whey are no drops coming over even though the distillate is boiling?

 If this happens at the beginning of the distillation, there is insufficient energy input to cause adequate vaporization of the liquid. In this case we should increase the heat.

 If this happens at the end of the distillation, almost all of the low boiling liquid has been removed. Solvent vapors trapped in the boiling stone pores will continue to be an ebullition source, causing bubbling.

 

 DISCUSION

Distillation is one of the oldest and still most common methods for both the purification and the identification of organic liquids. It is a physical process used to separate chemicals from a mixture by the difference in how easily they vaporize. As the mixture is heated, the temperature rises until it reaches the temperature of the lowest boiling substance in the mixture, while the other components of the mixture remain in their original phase in the mixture. The resultant hot vapor passes into a condenser and is converted to the liquid, which is then collected in a receiver flask. The other components of the mixture remain in their original phase until the most volatile substance has all boiled off. Only then does the temperature of the gas phase rises again until it reaches the boiling point of a second component in the mixture, and so on. The boiling point of a substance determined by distillation is a useful physical property for the characterization of pure compounds. At any given temperature a liquid is in equilibrium with its vapor. This equilibrium is described by the vapor pressure of the liquid. The vapor pressure is the pressure that the molecules at the surface of the liquid exert against the external pressure, which is usually the atmospheric pressure. The vapor pressure is a very sensitive function of temperature. It does not increase linearly but in fact increases exponentially with temperature. The vapor pressure of a substance roughly doubles for every increase in 10 °C. When the vapor pressure of the liquid equals the applied pressure, the liquid boils. Thus, the boiling point of a liquid is the temperature at which the vapor pressure equals the applied pressure. The normal boiling point of a liquid is the temperature at which the vapor pressure of a liquid equals atmospheric pressure (1 atm). The boiling point of a liquid is a measure of its volatility.

The successful application of distillation techniques depends on several factors. These include the difference in vapor pressure (related to the difference in the boiling points) of the components present, the size of the sample, and the distillation apparatus. Distillation relies on the fact that the vapor above a liquid mixture is richer in the more volatile component in the liquid, the composition being controlled by Raoul’s law: In an ideal solution the partial pressure (PA) of component A at a given temperature is equal to the vapor pressure Po A of pure A multiplied by the mole fraction of A (XA) in solution. Consider an ideal solution of

 A and B: XA = nA/ (nA + nB) , XB = nB/ (nA + nB) and XA + XB = 1

REFERENCES

 

•        https://www.jove.com/science-education/11201/simple-distillation
•        https://byjus.com/chemistry/distillation/
•         Harwood & Moody 1989, pp. 141–143
•        ^ Schaschke, C., 2014. A Dictionary of Chemical Engineering. Oxford University Press.
•        ^ 2019. Distillation: The Historical Symbol of Chemical Engineering. The University of Toledo. URL https://www.utoledo.edu/engineering/chemical-engineering/distillation.html
•       ^ 2017. Products made from petroleum. Ranken Energy Corporation. URL https://www.ranken-energy.com/index.php/products-made-from-petroleum/
•        ^ Gildemeister, E.; Hoffman, Fr.; translated by Edward Kremers (1913). The Volatile Oils. 1. New York: Wiley. p. 203.