Fractional Distillation Lab Name one piece of apparatus that is not used in a si

Question

Fractional Distillation Lab

Name one piece of apparatus that is not used in a simple distillation but is used in a fractional distillation. The temperature in the pot (the round bottom flask) and the head (the three-way adapter) are different during a distillation of a binary mixture. Is this correct? Why? In this digital age, the ability to read a scale is becoming a lost art. Our Abbe refractometers use just such an old fashioned scale. With a line of people behind you waiting to use the instrument, you will need to be able to quickly and accurately read your refractive index. What are the refractive indices, to four decimal places, of the three samples below? Consider an 80:20 mixture of A and B. What would be the boiling point of this mixture? What would be the composition of the vapors just above the boiling liquid? What would be the composition of the initial distillate collected from a fractional distillation of this mixture if the apparatus had a separation efficiency of three theoretical plates? How many theoretical plates would be needed in the distillation to be able to separate pure B from this mixture? Below are some real student data for Distillations of 40 mL of mixtures of cyclohexene (bp 81 degree C) and toluene (bp 111 degree C) performed in this laboratory in 1997. Which student performed a simple distillation of these substances? Which student distilled these substances, but had the thermometer placed too high in the 3-way adapter? Which student carried out a careful fractional distillation of a mixture of 30 mL cyclohexene and 10 ml toluene? Which student carried out a careful fractional distillation of a mixture of 20 mL cyclohexane and 20 mL toluene?

Explanation / Answer

1) A fractionating column is not used in a simple distillation but is used in a fractional distillation.

Explanation-A simple distillation apparatus consists of a boiling flask which is attached to an adapter holding a thermometer .The adapter connects to a condenser into which cold water is constantly passed through. The condenser leads into a collection flask for the purified liquid.

Fractional distillation is essentially the same as simple distillation except that a fractionating column is placed between the boiling flask and the condenser.

6)During fractional distillation of a binary mixture, the temperature in the pot is different from the temperature in the head, because temperature gradient is created. The higher up in the column, the lower the temperature. The temperature in the pot is higher. The separation is based on the boiling point differences of the components of the mixture, usually less than 25 0C.   Using a fractionating column which allows for repeated simple distillations two mixtures can be successfully separated.  

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