Post Lab Questions: Distillation (2 pt) Suppose you were going to perform a simp
ID: 717379 • Letter: P
Question
Post Lab Questions: Distillation
(2 pt) Suppose you were going to perform a simple distillation experiment in which the liquid mixture was colored green using a non-volatile organic dye. Would you expect the dye to stay in the source flask or collect in the receiving flask? Explain your answer to receive credit.
(2 pts) Explain (qualitatively) how the composition of the liquid mixture in the source flask changes during the course of a fractional distillation.
(1 pt) Explain why fractional distillation can be used to separate two miscible liquids with boiling points within 25 °C of each other, whereas simple distillation cannot normally be used for this purpose.
Explanation / Answer
Suppose you were going to perform a simple distillation experiment in which the liquid mixture was colored green using a non-volatile organic dye.I would expect the dye to stay in source flask because it is non-volatile. The volatile substance will only be collected in the receiving flask.
in a liquid mixture if one fraction boils at temperature A and another boils at higher temperature B, you will observe the thermometer temperature drop from A to a lower temperature before rising to B. This occurs because there is no fraction in the source flask being vaporized between temperatures A and B. That is to say that no vapor is generated between these temperatures, and because of its placement, the thermometer only reads the temperature of vapor that has risen up through the apparatus and is in contact with the thermometer. The temperature read by the thermometer does not represent the temperature of the liquid in the source flask, but rather the vapor temperature above the source flask surrounding the thermometer. Without vapor present, the thermometer cools until the next fraction is vaporized, at which point the thermometer reading will rise to the temperature of the vapor representing the next component, in this case,B.
Fractional distillation is a specific type of distillation that is typically used when trying to separate a mixture of liquids whose boiling points differ by less than 40 ºC. This lab utilizes fractional distillation because the boiling points of the impurities are unknown and could be close to the boiling temperature of acetone (approximately 56 °C). Ethanol for instance, is a common organic solvent that boils at 78 °C. If the waste acetone were contaminated with ethanol, fractional distillation would be required to separate the two components. The difference between fractional distillation and simple distillation is that the fractional distillation apparatus includes a fractionating column (in this case a condenser lightly packed with steel sponge) inserted between the source flask and the distillation head, providing greater surface area to ensure that the vapor of only one component, or fraction of the mixture reaches the second condenser. Additionally, fractional distillation requires the careful reading of vapor temperatures via a thermometer inserted into the top of the distillation head The temperature changes in the vapor during the course of a fractional distillation are very important because they are, in essence the boiling temperatures of the fractions in order of increasing temperature.