You will be given a test tube containing two immiscible liquids and a solid or- 3
ganic compound that is dissolved in one of the liquids. You will be told the identity of the two liquids and the solid compound, but you will not know the relative positions of the two liquids or in which liquid the solid is dissolved.
2 Do not place the litmus or pH paper into the sample; the dye will dissolve. Instead, place a drop of solution from your spatula onto the test paper. With this method, several tests can be per- formed using a single strip of paper.
3 The sample you are given may contain one of the following combinations of solid and liquids (the solid is listed first): fluorene, methylene chloride, water; triphenylmethanol, diethyl ether, water; salicylic acid, methylene chloride, 1 M NaOH; ethyl 4-aminobenzoate, diethyl ether, 1 M HCl; naphthalene, hexane, water; benzoic acid, diethyl ether, 1 M NaOH; p-aminoacetophenone, methylene chloride, 1 M HCl.
A) Without doing any experimental work, predict where each liquid is (top or bottom) and in which liquid the solid is dissolved. Justify your prediction. You may want to consult a handbook such as The Merck Index or the CRC Handbook of Chemistry and Physics to determine the molecular structure of a compound or to find any other relevant information. Note that dilute solu- tions such as 1 M HCl are composed mainly of water, and the density will be close to 1.0 g/mL. Furthermore, you should assume that the density of a sol- vent is not altered significantly when a solid dissolves in the solvent.
B) Now try to prove your prediction experimentally. That is, demonstrate which liquid the solid compound is dissolved in and the relative positions of the two liquids. You may use any experimental technique discussed in this experiment or any other technique that your instructor will let you try. In order to perform this part of the experiment, it may be helpful to separate the two layers in the test tube. This can be done easily and effectively with a Pasteur pipette. Squeeze the bulb on the Pasteur pipette and then place the tip of the pipette on the bottom of the test tube. Now withdraw only the bottom layer and transfer it to another test tube. Note that evaporating the water from an aqueous sample takes a very long time; therefore, this may not be a good way to show that an aqueous solution contains a dissolved compound. However, other solvents may be evaporated more easily. Explain what you did and whether or not the results of your experimental work were consistent with your prediction.
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