CHEM
Chem 278 Extraction Lab.docx

In part two we replaced water with 5 sodium

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like so benzoic acid only dissolves slightly in water because water is a polar molecule. In part two we replaced water with 5% sodium bicarbonate. Benzoic acid reacted with sodium carbonate to produce sodium benzoate, water and carbon dioxide (C 6 H 5 COOH + NaHCO 3 C 6 H 5 COONa + H 2 O + CO 2 ). In the presence of the water created by the reaction, sodium benzoate readily dissociates to form sodium ions and benzoic acid ions making it more soluble in water. After separating out the partitioned aqueous phase, 6M HCl was added to form a precipitate. The HCl is a strong acid and dissociates completely to react with the organic salt, re-forming the acid and an inorganic salt (Sodium chloride). The sodium chloride salt is soluble in water because the Na+ cation and the Cl- anion are attracted to the polar ends of water creating ions. However benzoic acid is now insoluble because the majority of benzoic acid is nonpolar and water is polar. By checking the pH and making sure it is acidic we can assume that all of the benzoic acid has precipitated out. After vacuum filtering the bezoic acid is recovered from solution. The K org is 0.1364 which is much smaller than part I. The reason for this is in part II the benzoic acid was mostly dissolved into the aqueous phase and not the DCM. Questions: 1. To separate benzoic acid from the methyl benzoate a method of base extraction can be used. An acid or base is added, and the pH of the aqueous phase is adjusted to bring the compound of interest into its required form much like we did in exercise II. 3. a.Extraction would work because sodium chloride is readily solable in water. However, paraffin wax is very nonpolar and will not dissolve in water. b. Extraction will work because decane is nonpolar and would be soluble in the DCM. Also pentaerytritol is a polar compound that would readily dissolve in water. c.Both sodium benzoate and sodium chloride are dissolvable in water making extraction not a good seperation technique d. Extraction will not work because both pentanol and hexanol are only slightly soluble in water.
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  • Fall '08
  • CZU
  • Solubility, sodium bicarbonate, Chemical polarity

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