Extraction Technique Quiz
1) 1) Consider the following solvent pairs. If mixed together, which pairs would form two layers? If they form two layers, which solvent would be on top?
- Hexanes and water
- Water and methylene chloride
- Hexanes and methylene chloride
- Methanol and hexanes
- Ethanol and water
- Acetone and toluene
2) You have 100 mL of water and add 4 mL of ether to it. You notice only one layer. Then, you add 6 mL more and see a small layer of a clear liquid on top of the water. Explain what is happening.
3) You want to extract a compound from water, and have determined that the compound is equally soluble in both hexanes and diethyl ether. Which solvent would be the better choice for the extraction?
4) The distribution coefficients for a compound are as follows:
- Kcyclohexane/water = 1.5
- Kpentane/water = 11.2
- Kdiethyl ether/water = 5.1
You have an aqueous mixture of the compound. Which solvent system, cyclohexane/water, pentane/water, or diethyl ether/water, would give the most efficient extraction into the organic solvent?
5) One gram of a compound requires the following quantities of solvent to dissolve: 47 mL of water, 8.1 mL of chloroform, 370 mL of diethyl ether, or 86 mL of benzene. Calculate the solubility of the compound in these four solvents (as g/100 mL). Estimate the partition coefficient of the compound between chloroform and water, ethyl ether and water, and benzene and water. Which solvent would you choose to extract the compound from an aqueous solution?
6) Five grams of Compound A is dissolved in 90 mL of water. The distribution coefficient for Compound A between hexanes and water is 5 (in other words, KCompound A(hexanes/water) = 5.)
- How much of Compound A will be in the hexanes if you extract it from the water one time with 90 mL of hexanes?
- How much of Compound A will be in the hexanes if you extract it from the water with three sequential extractions using 30 mL of hexanes each time, and then combine the hexanes extracts?
7) You carefully purified phenanthrene from a very long, complicated procedure. It took days. It is very important for you to hand the purified phenanthrene in to your TA in one hour to get a good grade. Oops! You accidentally put the phenanthrene into a vial which you thought was clean, but instead had a lot of NaCl clinging to the sides. What can you do to quickly purify the phenanthrene again?
8) Show the product of the following reactions. If there is no reaction, write "NR".
9) Which of the following compounds could be separated by acid-base extraction?
10) If you test an unknown organic compound and find it to be soluble in 5% aqueous NaHCO3, what functional group does it probably contain?
11) You are going to extract a compound into diethyl ether from water, using two successive extractions. Make a detailed step-wise summary of all operations in the procedure, paying attention to the location of the solute at each step and the position of each layer in the separatory funnel. Start with step 1 as "Put the separatory funnel in the ring on the ringstand."
12) Repeat the previous problem using methylene chloride as the extraction solvent.
13) Outline in a flowchart how you would separate the following compounds:
14) A reaction work-up for an aqueous reaction mixture calls for extraction first with diethyl ether and then a wash with saturated aqueous sodium chloride. What is the purpose of the saturated sodium chloride wash?
15) You have prepared an organic compound by reacting it with strong aqueous acid. The work-up calls for extraction into methylene chloride, then a wash with 5% NaHCO3. What is the purpose of the NaHCO3 wash?
16) What can you do if you do not know which layer is which in an extraction procedure?
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