Distillation and Boiling Point Determination Activity No. _____ INTRODUCTION Simple distillation is a process designed to evaporate a volatile liquid from a solution of non-volatile substances. With the application of heat, the vapor is condensed and collected in a receiving flask. The boiling point of the volatile substance must be known to be able to monitor the temperature of the vapor rising to the top of the distilling flask. The boiling point of a liquid refers to the temperature when its vapor pressure is equal to the external pressure. The normal boiling point is the temperature at which the vapor pressure of the liquid is equal to the standard atmospheric pressure, 1 atm. Since pure substances have a distinct boiling point, boiling points are sometimes used to determine the purity of substances. In this activity, a sample of wine will be distilled to be able to collect ethanol. The boiling point of the distillate will be determined and compared with that of pure ethanol. The distillate will also be tested for the presence of ethanol using simple chemical tests. OBJECTIVES At the end of the t he experiment, the students should be able to: 1. 2. 3. 4.
Perform simple distillation. Determine the boiling point of the distillate. Use the boiling point of a sample as an indication of its purity. Perform tests for the presence of alcohol in the distillate.
MATERIALS Reagents acidified K 2Cr2O7 ethanol wine Apparatus 1 distilling flask condenser adapter 3 rubber stopper 2 burner 2 thermome thermometer ter 3 Iron stand
2 Iron ring 2 wire gauze 2 rubber tubing 1 250 mL Erlenmeyer flask 1 100 mL Graduated cylinder 1 trough 1 water pump
2 small test tubes 2 dropper 1 funnel 1 capillary tubing 1 rubber band 1 100 mL beaker 3 iron clamp
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Bicol University College of Science DEPARTMENT OF CHEMISTRY
PROCEDURE A. Simple Distillation 1. Assemble the set-up as shown in the diagram on the next page. Half-fill (~170mL) the distilling flask with the wine sample and put boiling chips. Connect the rubber tubing to the water inlet and water outlet of the condenser and let water flow inside the water jacket of the condenser. Make sure that the water output rubber tubing has the necessary receiver of the water coming from the condenser. Heat the distilling flask and maintain the temperature at 78.3ºC. Collect about 10 mL of distillate or until vapor ceases to condense. 2. Record the volume of the distillate and calculate for % yield.
B. Test for Alcohol 1. Place 10 drops of the distillate in a test tube. Add 10 drops of acidified K 2Cr2O7 or until a color change is observed. What color change did you observe? 2. Place 1mL of the distillate to an evaporating dish and ignite. Record your observation. C. Boiling Point Determination 1. Heat one end of a capillary tube until it closes. 2. Make a test tube assembly by using the following directions and illustration below. a. Place about 1 mL of ethanol in a 10-12mm diameter test tube. b. Using a small rubber band, attach a thermometer to the outside of the test tube. The thermometer bulb should be even with the test tube's bottom. c. Insert the capillary tube into the test tube in an in verted position.
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Bicol University College of Science DEPARTMENT OF CHEMISTRY
3. Make a water bath assembly by using the following directions and illustration.
a. Half fill a 100 mL beaker with tap water. Place the above test tube assembly in the water bath so that the level of the alcohol in the test tube is beneath the surface of the water bath. b. Heat the water bath with continuous stirring to ensure even heating. There will be an initial stream of bubbles as dissolved air is expelled. Then, a little later, a rapid stream of bubbles emerges from the capillary tube. At this point, stop heating and begin observing the stream of bubbles. c.
Soon the stream of bubbles will slow down and stop. When they stop, the liquid will enter the capillary tube. This point corresponds to the boiling point of t he liquid. Record this value under trial 1.
3. Cool the water bath for a few minutes and repeat the heating p rocess using another capillary tube. . Record the temperature reading as trial 2 and average the values of the two trials. 4. How does your observed boiling point compare with the accepted boiling point of ethanol? Calculate your percentage error.
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Bicol University College of Science DEPARTMENT OF CHEMISTRY
Name ____________________________________________________ Co-workers _____________________________________________ _____________________________________________
Date Started ________________________ Date Finished _______________________ Group/Section ______________________
DATA AND RESULTS
DATA TABLES Volume of wine used (mL) Volume of distillate (mL) % Yield Color of distillate with acidified K 2Cr2O7 Flammability test Boiling pt. of distillate (ºC) Trial 1: Trial 2: Average: Boiling pt. of ethanol (°C)
78.3
% error Calculations:
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Bicol University College of Science DEPARTMENT OF CHEMISTRY
POSTLAB QUESTIONS 1. How were you able to collect ethanol in this activity? Explain the process. 2. How did the boiling point of the distillate compare with the boiling point of ethanol? 3. What is the importance of boiling point determination of organic substances? 4. What tests were performed to confirm the presence of alcohol in the d istillate? Write the chemical equations.
