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Analytical Chemistry Experiment: Determination of the Boiling Point of Wine

December 21, 2008

Analytical Chemistry Experiment

Determination of the Boiling Point

Abstract

After the preparation of capillary tubes and through the adaptation of simplified Siwoloboff method, few drops of pineapple wine sample were placed in a centrifuge tube.  The capillary tube which is sealed end up was immersed in the sample.  The centrifuge tube is then attached to the bulb of the thermometer.  The tube – thermometer was placed in a oil bath added with few pieces of boiling chips, heated, and occasionally stirred in order to ensure uniform distribution of heat.  A close observation took place and at which the first bubble leaves the capillary tube, the temperature was recorded. Do two trials…


I. Introduction

Several factors enter into determining the boiling point, and the molar heat of vaporization, of a hydrocarbon. Hydrocarbons containing  more than 6 carbon atoms in a linear chain depend upon chain entanglement in addition to the factors that also play a role in hydrocarbons containing less than 6 carbon atoms in a linear chain. For the smaller hydrocarbons, the forces holding the liquid together are similar, primarily van der Waals interactions. However, in addition, the degree of non-ideality of the vapor phase, and the globular shape of the molecule. The more symmetric molecules tend to be more volatile.

The boiling point of a liquid is the temperature at which the liquid and vapor phases are in equilibrium with each other at a specified pressure. Therefore, the boiling point is the temperature at which the vapor pressure of the liquid is equal to the applied pressure on the liquid. The boiling point at a pressure of 1 atmosphere is called the normal boiling point.

II. Review of Related Literature

Siwoloboff Method

Principle

A sample is heated gradually in a tube which is immersed in a liquid bath. The sample tube is held in close contact with a thermometer and it contains a boiling capillary which is fused about 1 cm above its lower end. Upon approach of the boiling temperature bubbles emerge rapidly from the lower open end of the capillary. The boiling temperature is that temperature at which, on momentary cooling, the string of bubbles stops and liquid suddenly rises in the capillary.

Procedure

The bath liquid is chosen according to the expected boiling temperature of the test substance. Silicone oil can be used for temperatures up to 573 K. Liquid paraffin may only be used for

Temperatures up to 473 K. At first, the heating of the bath should be adjusted to a temperature rise of 3 K/min. The bath must be stirred. At about 10 K below the expected boiling temperature, the heating is reduced so that the temperature rise is less than 1 K/min. Upon approach of the boiling temperature, bubbles begin to emerge rapidly from the capillary. The boiling temperature is that temperature at which, at momentary cooling, the string of bubbles stops and fluid suddenly rises in the capillary

OECD Guidelines for the Testing of Chemicals 1995

III. Methodology

1.)    Prepare 2-3 capillary tubes, sealing one end with the use of a Bunsen burner.

2.)    Adapting the simplified Siwoloboff method, place a few drops of the sample in a centrifuge tube. A capillary tube, its sealed end up, is immersed in the sample. The centrifuge tube is then attached to the bulb of the thermometer.

3.)    The tube-thermometer is then placed in an oil bath. Add a few pieces of boiling chips to the bath.

4.)    Heat the oil bath with a small blue flame, occasionally stirring it, to ensure uniform distribution of heat.

5.)    Closely observe and record the temperature at which the first bubble leaves the inverted capillary tube. Then record the temperature when the liquid sample enters the tube, just as the last bubble leaves it. This is the so-called boiling point range.

6.)    Do a second trial repeating steps 2 to 5.

IV. Discussions of Data and Interference from Results

T1/°C

T2/°C

Sample 1

72°C

80°C

Barometric Pressure

765 mmHg

The sample we used has the range 72°C  to 80°C in 765 mmHg, while the boiling point of ethanol in 760 mmHg is 78.5°C. We could not really tell whether the sample we used was pure for we are not in the atmospheric pressure.

V. Answers to Guide Questions

  1. How closely did your corrected boiling point agree with the literature boiling point for the known compound? What are some possible errors in this experiment?

Boiling point of ethyl alcohol is about 78.5 °C and our boiling point ranges between 72 °C to 80 °C.

There are many possible sources of error in this experiment. It can be human error and instrumental error.

One of the causes of errors in determining the boiling point I found which can change our observed value is the barometric pressure. The literature boiling point of ethanol is about 78.5 °C in 760 mmHg while our boiling point was in 765 mmHg.

  1. Which parameter gave the best correlation with experimental boiling point in the modeling experiment?
  • Based on the experiment, I observed that the closer the atmospheric pressure to the normal pressure, which is 760 mmHg, the closer the value of the temperature to the normal temperature of ethanol. This is the factor that may affect the result of the experiment in the determination of Boiling Point.
  1. Based on your modeling results, is boiling point dependent on thermodynamic stability?
    • No, boiling point is not dependent on thermodynamic stability. The boiling point of a compound can only be determined by physical means.
    1. For your particular set of compounds, what conclusions can you draw about how structural features affect boiling point?
    • On how structural features affect boiling point, I therefore conclude that, the longer the chain of hydrocarbons is, the higher the boiling point of the compound.

    VI. Bibliography

    • Zubrick, James W. The Organic Chemistry Lab Survival Manual: A Student’s Guide to Techniques 6th Edition. New York: John Wiley & Sons Canada, Ltd.; 5th edition.

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