Procedures The experiment was performed as stated in the course textbook: Pavia, D. Pp 51— Data The distillation curves for our simple and fractional distillation See page 3 clearly demonstrate that fractional distillation separates the two compounds more completely.
fractional distillation equipment
The boiling point bp of our unknown compounds was taken from the flat regions of the fractional distillation curve. Analysis via gas chromatography allowed us to determine the relative percentage of hexane and toluene at fractions near the beginning and end of our distillations. Relative percentages have been recorded in the table below, and our calculations are shown on page 5.
We found that while the simple distillation separated the majority of the two compounds near the beginning and the end of the distilling process, fractional distillation produced much more pure fractions. In simple distillation the column was shorter, allowing less room for the two different compounds to fully separate. While heating the round-bottom flask the hexane molecules gain higher kinetic energy faster than the toluene molecules due to their lower molecular weight and lesser intermolecular forces.
The longer fractional distillation column allowed the hexane molecules with higher kinetic energy to separate from the lower-energy toluene molecules. After viewing the gas chromatograph data from the fractional distillation we saw that our unknown compounds had almost completely separated, while the fractions from the simple distillation were less pure.
Although distillation is a good separation technique it is still necessary to ensure that proper steps are taken to reduce the chances of error. Failure to add a boiling chip to the round-bottom flask could allow the mixture to heat unevenly. This could allow molecules with a higher boiling point to gain kinetic energy before the molecules with the lower boiling point, which would create impure fractions. Watching the rate of temperature increase is also important. Allowing the temperature to increase too quickly can cause impurity for the same reason.
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We forgot to add the boiling chip to the round-bottom flask in the simple distillation, which could have contributed to the mixture of toluene and hexane that we saw. We made sure to include the boiling chip in the fractional distillation, however, and did not observe any problems. Simple distillation systems have, by definition, one theoretical plate at best, possibly even less when not run optimally. On the other hand, well-designed and run systems can have or more theoretical plates. These come most often in the form of spinning band or packed columns see the implementation section below and can purify compounds up to This diagram shows the purification power vs.
(DOC) Sample Lab Report Simple and Fractional Distillation | Nur Natasha - bumbreatepvilu.ml
This is primarily relevant in vacuum fractionation or fractional distillation. The difference in pressure is caused by the gas flow resistance that the column represents. So, regardless of the performance of the vacuum pump, a given distillation design in a particular distillation application has inherent limits due to its gas flow characteristics. Depending on system design and operating conditions, this can be fairly high — as in multiple millimeters of mercury. However, temperature-sensitive compounds may not survive or suffer in quality.
Since raising temperature may not be an option, only columns with a small pressure drop should be applied in these cases. The amount of condensed distillate allowed to flow back into the system relative to the amount of distillate collected. Practical reflux ratios are typically between to Packed and tray columns typically have a much higher holdup than Vigreux or Spinning Band columns. One might tend to think, that the compounds in the mix going in are going to come out, purified to This chapter will attempt to describe the physical reality without going too deep into the math involved.
As has been observed by early scientists, the partial vapor pressure of each compound determines both order as well as purity of the fractions coming out of the apparatus, the nature of which also has a major influence on the outcome i. In a simple distillation of a binary mix with components L and H with different boiling points, on heating, the mixture will come to a boil at a temperature between those points.
At that point, the vapor contains a higher fraction of the lower-boiling compound L. However, this ratio changes over time due to the mix in the boiling flask getting depleted of L. The temperature of the liquid will also rise towards the boiling point of H in the course of the distillation. Also, the vapor created gets richer in H until, towards the end, almost pure H gets distilled over.
Conversely, in fractional distillation again, with a binary mix as above the vapor gets condensed and re-evaporated multiple times across the length of the column, due to the feedback of liquid in an amount fitting to maintain intimate contact and creation of an equilibrium between vapor rising and liquid flowing back.
This has approximately the same effect as multiple simple sequential distillations in one operation, i. One is obvious, increased equipment cost and operational complexity. This is a necessary compromise between the duration of the operation and efficiency of the operation, i.
The more volatile liquid the liquid with the lower boiling point will typically evaporate first and the vapor will pass into a condensing column, where it can revert into a liquid condense on the cool glass where it trickles into a collection flask.
Heating further will cause the less volatile liquids to evaporate and distill at higher temperatures. The two main kinds of distillation are simple distillation and fractional distillation , and both are used widely. What is simple distillation? The setup for a simple distillation is shown in Figure 1.
A simple distillation apparatus consists of a boiling flask round-bottom flask attached to an adapter holding a thermometer to determine the boiling temperature of the liquid. The adapter connects to a condenser into which cold water is constantly passed through.
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The condenser leads into a collection flask for the purified liquid. What is fractional distillation? Fractional distillation is essentially the same as simple distillation except that a fractionating column is placed between the boiling flask and the condenser. The fractionating column is usually filled with glass or plastic beads.
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