Organic Lab Report: Separation Of Hexane And Toluene Of Liquids PDF

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Separation of Hexane and Toluene of Liquids by Simple and Fractional Distillation CHEM 223 Organic Chemistry Lab 1 Walmecka Lee

Abstract:

The objective of this experiment is to separate two components of a mixture by applying and fractional distillation tequniques. First, a 20 mL solution of 1:1 volume ratio of toluene and hexane is separated using simple distillation apparatus. Applied heating of the solution causes hexane to boil and depart the distilling flask first ( boiling point: 69C). When all the hexane has vaporized, a temerapture increase signals boiling of toluene (boiling point:110C). Two collection of condensed hexane vapor (S1) and condensed toluene vapor (S2) from the distillation process are ran through gas chromatography (GC). Each GC produce two distinct peaks, with the area under each peak given. Next, are the 20 mL of 1:1 tolunese and hexane are distilled using fractional distillation. Two collections vials of hexane condensate (F1) and toluene condensate (F2) are processed by GC. The GC results also reveal two distinct peaks of F1 and one peak of F2 and their areas. The areas from both types of distillations are used to compare the percentage of hexane and toluene in S1, S2, F1 and F2 from simple and fractional distillations, respectively. Fraction distillation yields higher fraction of hexane in F1 and higher fraction of toluene fraction in F2; therefore produces better separation of hexanane and toluene with respect to their boiling point difference of 41C. The purpose of this experiment is to practice separation of a binary (two) liquid mixture of Hexane and Toluene. Hexane and Toluene have boiling points that are relatively far apart with hexane having a bp (boiling point) of 69°C and Toluene with a bp of 111°C. This experiment will help us develop skills with operating a semimicrodistillation apparatus so that purifications required in later experiments are more successfully carried out.

Introduction: A chemist’s goal is to separate two chemical components in a solution can be accomplished by exploiting the volatility charcateistics of liquids. Recognizing the difference in boiling point of the different chemicals allow those components to be separated using a technique called distillation. Distillation is the process of vaporizing and condensing out a component from a mixture solution. Chemicals with significant differences in boiling point of 25C or greater can be sufficiently separated using simple distillation. A boiling point (BP) difference of less than 25C prefers fractional distillation for qualitative separation. Fractional distillation utilizes fractional columns that yield greater surface area and allow more gas-liquid equilibrium. This helps recondensation of higher BP component while the lower BP component is still proceeding. In this experiment, two solutions of hexane and toluene are separated using simple distillation and fractional distillation, respectively. The distillation products collected from each teqhnique will be ran through gas chromatography. Comparing the perfect compositions of hexane and toluene in each product will be determined whether simple or fractional produces better separation.

Data Table 1: Simple Distillation 1st fraction (@ 65.1°C) 2nd fraction (@ 95.3°C) 3rd fraction (@ 105.1 °C)

(Raw data @ 21.7 °C) 1.3930 1.4971 -

(Adjusted data @ 20.0°C) 1.3937 1.4978 -

Data Table 2: 1st Refraction:

Fraction 1 Redistillation

(Raw data @ 21.7 °C)

(Adjusted data @ 20.0°C)

1st fraction (@ 69.0°C)

1.3841

1.3845

Data Table 3: 2nd Refraction:

Fraction 3 Redistillation

(Raw data @ 21.1 °C)

(Adjusted data @ 20.0°C)

2nd fraction (@ 109.5°C)

1.4975

1.4965

Procedures and Observations: Figure A:

Figure B: Hickman still with Claisen head adapter.

Results: 

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Obtained a 5mL conical vial, automatic pipet, and clear colorless stock solution (Hexane and Toluene). Used an automatic pipet to pipet 2000 µL (2 mL) of the colorless stock solution into the stoppered 5-mL conical vial. Added a boiling stone into the 5-mL conical vial. (1) Assembled a Hickman still head with sidearm to a claisen head and 1-mL conical vial as shown above in figure B. NOTE: Also attached a thermometer adapter above claisen head as shown in Figure A. (1) Turned on hot plate and raised the sand bath to 80-90°C at a maximum rate of 5°C/min. Once the sand bath thermometer reached 70°C, lowered rate to 2°C/min. A clear colorless

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liquid started to form in the trough of the Hickman still head. Extracted clear colorless liquid with a filter pipet into a 3-mL conical vial and recorded temperature of the sand bath thermometer at 97.4°C. Noted as first of two fractions (forerun). (1) Continued boiling of colorless solution until trough filled again. Extracted clear colorless solution again at 142.0 °C with a filter pipet into a screw-capped vial. Recorded this as second fraction. (1) Finished boiling rest of clear colorless solution in the temperature range of approximately 170°C for the sand bath. Extracted the rest of the clear colorless solution from the trough of the Hickman still with a filter pipet and placed into 3-mL conical vial. Recorded temperature of the sand bath at 173.1 °C. Turned off hot plate to allow for clean up later. Performed a refractive index for both the first and third fractions and recorded appropriate temperatures. Discarded second fraction. (1)

Discussion: In this experiment the data colletcted indicates that the experiment was successful in preparing and isolating a binary liquid mixture of Hexane and Toluene using a semimicrodistillation apparatus. For the first fraction the acquired refractive index of 1.3937 (adjusted to 20°C), which differs from the literature value (1.3751) by approximately 0.0186 units. With our redistillation, we were able to make our first fraction almost entirely pure of hexane instead of slightly impure as shown in week 1. The refractive index of the third fraction was 1.4957 (adjusted to 20°C). The third fraction only differed from the literature value (1.4961) by 0.0017. This reflected how the third fraction was only slightly impure to begin with. On the redistillation of the third fraction the refractive index of the second fraction was 1.4965 (adjusted at 20°C). This differed from the literature value (1.4961) by only 0.0004, which is almost pure toluene. This data supports the experiment success of the redistillation by showing the straddegy to acquire almost pure toluene. Given our data, it can be concluded that this experiment was very successful in isolating the binary liquid mixture of Hexane and Toluene.

Conclusion: In order to separate the liquids hexane and toluene from each other in this experiment, both simple distillation and fractional distillation was used. When comparing the data, analazying that one method was significantly more successful than the other. The one that was more effective was fractional distillation was executed and resulted in a better separation than Simple Distillation. After turning on the hotplate and slowly raising the temperature 5°C per minute, the 2 mL mixture of hexane and toluene began boiling and vaporizing at 65°C. The temperature kept increasing 1°C per minute. As the vapor temperature steadied at 69°C, the vapor started traveling to the Hickman still head and liquified. The first fraction was collected when the vapor temperature was 69°C and the sand bath temperature was 95°C (see table 2). The temperature dropped a little because the thermometer was no longer in contact with any vapor. Then, the vapor temperature gradually increased again. Once the sand bath reached 121°C, the liquid started vaporizing again. At this point the vapor temperature was at 101°C. After a few minutes, the vapor temperature was steady at 105°C and the liquid was in the Hickman still. Fraction 2

was collected when the vapor temperature was 105°C and the sand bath temperature was 125°C (see table 2). Finally, the refractive index of each fraction was determined. Table 4. Temperatures each fraction was collected at and RI. Fractions 1 2

Vapor Sand bath Temperature Temperature 69°C 95°C 105°C 125°C

Refractive Index 1.3945 1.4915

Fraction 1 had a refractive index of 1.3945 and a boiling point of 69°C. When comparing the experimental values to table 1, it can be concluded that fraction 1 is hexane. Fraction 2 had a refractive index of 1.4915 and a boiling point of 105°C. When comparing this data to table 1, it can be determined that fraction 2 is toluene. Even though the boiling point for fraction 2 is lower than the literary boiling point for toluene, fraction 2 can still be determined as toluene because the refractive index was extremely close. In the textbook, it stated that three fractions should have been collected. Even though only two fractions were collected, the purpose of the experiment was still successfully completed because the two substances were separated into nearly pure components. Only two fractions were collected because the mixture completely evaporated before a third fraction could be extracted. However, if three fractions were collected it can be presumed that one of them would have still been a mixture of hexane and toluene. In conclusion, this experiment can be used to identify what pure liquids make up a mixture.

References: 1. Haynes, W. M. (Ed.) handbook of Chemistry and Physics, 94th ed. CRC Press: Boca Raton, FL, 2013. 2. Hexane (Oct. 2017) In Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Toluene 3. Toluene (Oct. 2017) In Wikipedia. Retrieved from https://en.wikipedia.org/wiki/Toluene...