Simple Distillation Lab 2 PDF

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LAB 2 REPORT (SIMPLE DISTILLATION) CHEM 221...

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Introduction This lab's goal is to identify an unknown petroleum hydrocarbon. This can be accomplished by purifying the compound using simple distillation, which will allow the boiling point, refractive index, and density of the compound to be determined. Petroleum can be separated into its constituents using simple distillation, which separates the components of a mixture based on differences in boiling points (Klein, 2021). Boiling point will be closest to the median boiling point found during distillation. It will be determined after distillation using a capillary-tube method, semi-microscale boiling point measurement. These measurements will help identify the name of the compound. Boiling point is an intermolecular force (Graham et al., 2016). The greater the number of carbons in an organic compound, the higher its boiling point. One of the most important physical properties of a compound is its density. It is a property that remains constant regardless of the amount of substance present. This allows for chemical compounds to be identified (Graham et al., 2016). The ratio of the speed of light in vacuum to the speed of light in the substance is known as the refractive index, n (n = cvac/cliq). It is also related to the incident beam (ray of light before entering liquid) to refracted beam (ray of light after entering liquid) angle ratio (n = sinθvac/sinθliq). The index of refraction of a compound can help determine its identity as a result of light entering it at a specific angle or slowing down to a specific speed, depending on its composition (Introductory Organic Chemistry I Laboratory Manual). To identify an organic compound, we can use: -

Spectral evidence (presence of functional groups)

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Chemical evidence (chemical reaction)

-

Physical evidence (boiling point, index of refraction, density, etc.) This lab is intended to identify an alkane or cycloalkane, which are unreactive chemical

compounds with non-revealing functional groups. As a result, analyzing their physical properties

is the most effective way to distinguish them (Introductory Organic Chemistry I Laboratory Manual). Results Barometric pressure = 756 torr State

Time (min)

Temperature (°C)

Initial

0:00

20

Condensation begins

15:00

77

Median boiling point (half distilled)

17:00

78

Fully distilled

19:00

79

Temperature of purified hydrocarbon after distillation = 20°C Figure 1. Distillation table Name

bp

nD20

d20

cyclopentane

49

1.4065

0.746

2,2-dimethylpentane

50

1.3688

0.649

2,3-dimethylbutane

58

1.3750

0.662

3-methypentane

63

1.3765

0.664

hexane

69

1.3749

0.659

methylcyclopentane

72

1.4097

0.749

2,4-dimethylpentane

80

1.3815

0.673

cyclohexane

81

1.4266

0.779

2,3-dimethylpentane

90

1.3919

0.695

heptane

98

1.3877

0.684

2,2,4-trimethylpentane

99

1.3915

0.692

methylcyclohexane

101

1.4231

0.769

(bp = boiling point in °C, nD20 = refractive index at 20°C, d20 = density at 20°C) Figure 2. Table 8.2 List of possible hydrocarbons

Name

bp

nD20

Unknown #3

79

1.4256

20 D

(bp = boiling point in °C, n

d20 0.730 20

= refractive index at 20°C, d = density at 20°C)

Figure 3. Table with unknown hydrocarbon data

Trial #

Mass (g)

Volume (mL)

Density (g/mL)

1

0.686

1.00

0.686

2

0.730

1.00

0.730

3

0.773

1.00

0.773

Figure 4. Table of densities found Average density = (0.686 + 0.730 + 0.773)/3 = 0.730 g/mL

Condensation (°C)

Boiling Point (°C)

77

79

Figure 5. Semi-microscale boiling point measurement

Cyclohexane physical properties

Accepted value

Experimental value

% error calculation = |[(experimental value accepted value )/accepted value]|*100

% error

Bp (°C)

81

79

|[(79-81)/81]|*100

2.47

Density (g/mL)

0.779

0.730

|[(0.730-0.779)/0.779]|*10 0

6.29

Refractive index

1.4266

1.4256

|[(1.4256-1.4266)/1.4266]| *100

0.07

Boiling point - median boiling point = 79 - 78 = 1 Discussion The physical properties used in this experiment are: boiling point, density, and refractive index respectively. All of these measurements will be determined after purification of the mixture, which is accomplished through simple distillation. A liquid mixture, containing small amounts of impurities, is vaporized in one container and then condensed in another during simple distillation (Introductory Organic Chemistry I Laboratory Manual). When the total pressure of the vapor equals the external pressure, the mixture with different vapour pressures will boil. In this scenario, however, there will be a higher proportion of volatile compound in the vapor, as well as in the liquid condensed in the other container. Essentially, this is driven by the lower boiling point of the more volatile compound. Boiling occurs at a temperature that is slightly higher than the boiling point of the more volatile component. A distillation system has to be set up: -

Thermometer

-

Thermometer adapter

-

Still head

-

Condenser with water inlet and water outlet

-

A boiling container

-

A vacuum adapter

-

A receiving container The boiling container is filled with the unpurified mixture and a boiling chip. Boiling chips

are added to speed up the boiling process. The heating apparatus is placed beneath the boiling flask, and the heating of the mixture begins. Temperatures should be recorded after the start of

distillation, when half of the liquid has distilled, and when the container is nearly dry but the temperature has not begun to drop. Distillation can be stopped once the boiling container is dry. The heating plate was set up at 100°C for the first 10 minutes, but no change was observed. Temperature was raised to 110°C for the next 3 minutes, no change was still observed. Finally, temperature was set to 118°C after 14 minutes. Condensation was observed after 15 minutes. Half of the liquid mixture was distilled after 17 minutes and full distillation was reached after 19 minutes. Following that, the temperature of the purified compound is checked with the thermometer. This ensures that it is at about 20°C (Introductory Organic Chemistry I Laboratory Manual). The mass of the unknown must be measured by adding 1.00mL of the distilled product to a clean vial. It is important to repeat this three times, with the density calculated as the average of the three densities found using the three mass measurements (Introductory Organic Chemistry I Laboratory Manual). Index of refraction is measured by adding a drop of purified hydrocarbon on a refractometer between two prisms until a clear visual field is formed, with one half being light and the other half being dark. Thereafter, the index of refraction and temperature displayed on the machine should be noted (Introductory Organic Chemistry I Laboratory Manual). Boiling point is determined via capillary-tube method, semi-microscale boiling point measurement. 2-4 drops of the purified hydrocarbon are added to a capillary tube, which is inserted into a boiling tube. The liquid is shaken to force it down the boiling tube. Once the assembly has been placed inside a digital boiling point apparatus, it can be observed when the liquid condenses, boils, and evaporates (Introductory Organic Chemistry I Laboratory Manual). The objective of this procedure was to identify an unknown petroleum hydrocarbon. The exact amount of liquid mixture provided was not given. Thus, recovery cannot be determined by calculation. However, it can be determined that a good percentage of recovery was obtained by

observing that the median boiling point is 1-2 degrees of difference from the boiling point, which is what was expected for a successful procedure. The results indicate that the unknown is cyclohexane, indicating that the objective was achieved. Conclusion The unknown provided was cyclohexane. The result is quite conclusive, given that the percent error for boiling point and refractive index are quite low (2.47% and 0.07%). The density percent error is a little on the higher side (6.29%), but still within the acceptable range. Errors may have occurred due to different factors: ●

During semi-microscale boiling point measurements, it is possible that air bubbles were mistaken for vapour bubbles, leading to a percent error in the boiling point.

●

Density measurements can be inaccurate if temperature changes are not taken into account. This is due to the fact that temperature affects density. References

(1) Graham, S. T. W.; Fryle, C. B.; Snyder, S. A. Organic Chemistry; Wiley: Hoboken, 2016. (2) Klein, D. R. Organic Chemistry; Wiley: Hoboken, NJ, 2021. (3) University, C. Introductory Organic Chemistry I Laboratory Manual; Concordia University: Montreal, QC, 2021....