CHM142 experiment5a - ABSTRACT Another type of purification...

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ABSTRACT Another type of purification technique used in the laboratory is extraction. This method requires different solubilities of compounds in water versus a water-immiscible organic solvent. At first part, we visualize the effect of adding inorganic salt into a mixture of two immiscible liquids containing an organic solute. Two liquids water and n-amyl alcohol mixed and formed immiscible mixture into two test tubes where water is denser. Neutral organic salt, crystal violet was then put on each container forming a homogeneous phase, dark violet in color. After this, NaCl was mixed into one of the container. It is observed that the water portion of the mixture became light violet while the color of n-amyl alcohol portion became more pronounced. Afterwards, we perform extraction. The adipic acid was titrated using the prepared NaOH. Subsequently, two other titration of adipic acid was made but after going through extraction with ether. For these two titrations, extraction is done once and twice accordingly. At the end, the effects of number of extraction in distribution of coefficient and the percentage yield of the organic substance was determined. INTRODUCTION One process that is useful for separation and purification of organic compounds from a mixture is known to be liquid-liquid extraction. Extraction is one of humankind’s oldest chemical operations. The preparation of a cup of coffee or tea involves extraction of flavour and odour components from dried vegetable matter with hot water. Aqueous extracts of bay leaves, stick cinnamon, peppercorns, and cloves are used as food flavourings, along with alcoholic extracts of vanilla and almond. For the last century and a half, organic chemists have been extracting, isolating, purifying and then characterizing the myriad compounds produced by plants that have been used for centuries as drugs and perfumes. When a solution of a solute in a solvent is shaken with another solvent, which is immiscible with the first, the solute distributes itself between the two solvents in proportion to its solubility in two pure solvents. Thus, a constant ratio is set up between the concentrations of the solute in the two phases or immiscible solvent layer. This equilibrium ratio can be represented by the equation: where K d is the distribution coefficient, while C 1 and C 2 are the concentrations of the solute in two solvents. These concentrations are expressed in g per mL. K is approximately constant for all concentrations of C 1 and C 2 . However, K will vary with temperature as solubility is temperature dependent. The solubility of a substance particularly in aqueous phases can be decreased by the addition of neutral salts that reduce the solubility of the substance in that phase.
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In this type of separation technique, choosing an appropriate extracting solvent is also crucial. Properties of desirable extracting solvents are: (1) should be immiscible or very sparingly soluble
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This note was uploaded on 04/27/2011 for the course CHM 142 taught by Professor Ng during the Spring '11 term at Mapúa Institute of Technology.

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CHM142 experiment5a - ABSTRACT Another type of purification...

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