Experiment 4: Extraction of Acidic & Neutral Compounds via Liquid-Liquid Extraction & Thin-Layer Chromatography

Question 1

When doing a microscale boiling point determination, when should the temperature be read for the boiling point measurement?

Answer 1

when the last bubble escapes the pm capillary tube and liquid is sucked back into the tube

Question 2

Which of the following would be the best procedure for extracting acetaldehyde from an aqueous solution?

Answer 2

3 successive extractions with 33.3 mL portions of ether

Question 3

Which of the following should be done before, during and/or after an extraction?

Answer 3

Check that the separatory funnel is properly assembled. This includes placing a rubber O ring between the Teflon washer and Teflon nut on the stopcock to avoid leaks.

Question 4

A student reported the following amounts of her compound recovered with each of 3 successive extractions using the same volume of solvent each time: 0.45 g, 0.23 g, 0.30 g. Based on your understanding of the partition coefficient, why can’t this be correct?

Answer 4

She should’ve obtained smaller amounts of compound with each successive extraction.

Question 5

If you did all of the reading, then you know about the partition coefficient of a compound and how that affects the ‘completeness’ of each extraction. Without doing calculations, what is the big take home message that the calculations show you for each successive extraction?

Answer 5

Using multiple smaller volume extractions extracts a greater mass of the compound than does one larger volume extraction.

Question 6

! Suppose an extraction with methylene chloride (d = 1.33 g/mL), also called dichloromethane, is performed with the desired compound initially in brine (d = 1.04 g/mL). In a separatory funnel, which layer will be the organic layer?

Answer 6

the bottom layer

Question 7

Which of the following demonstrates the proper use of a separatory (“sep”) funnel during washings and/or extractions?

Answer 7

all of these

Question 8

During gravity filtration, a student forgets to heat the solution before running it through the filter. After capturing the filtrate, the student analyzes the sample by spectroscopy and finds none of the desired product in the filtrate. What likely occurred to the student’s product?

Answer 8

the product precipitated and is present in the residue

Question 9

Often, saturated sodium bicarbonate solution is used to do a wash during the extraction process. What is a saturated sodium bicarbonate solution?

Answer 9

It is NaHCO3 dissolved in water to a point that no more of it can dissolve in the water.