Extractionworkshopkey

Extractionworkshopkey - Chemistry 14CL Extraction Workshop...

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Chemistry 14CL Winter 2008 Extraction Workshop Key 1. The solubility of benzoic acid in water is 3.4 g/L; in carbon tetrachloride it is 33.3 g/L. The pH of a saturated solution of benzoic acid in water is 2.8. (a) Calculate the K a for benzoic acid. Answer: Concentration of benzoic acid = 3.4g/122.2g mol -1 = 0.028 M [H+] = 10 -2.8 = 1.58 x 10 -3 K a = [H + ] 2 0.028 - [H + ] [H + ] 2 0.028 = (1.58 x 10 - 3 ) 2 0.028 = 8 .9 x 10 - 5 (b) Calculate the partition coefficient for benzoic acid in a water-CCL 4 solvent pair. Answer: K {organic/aqueous) = 33.3/3.4 = 9.8 (c) What weight of benzoic acid would be transferred to an aqueous phase if 1 g of benzoic acid were dissolved in 100 mL of carbon tetrachloride and the solution were extracted with 100 mL of water? Answer: 9.8 = (1-x)/x; x = 0.092 g (d) The solubility of benzoic acid in a 0.1-M solution of NaOH is 12.2 g/L. Explain why this is so much larger than the solubility in water. Answer: Benzoic acid reacts with the base to form the benzoate salt, which is more soluble in the aqueous phase than in the carbon tetrachloride. (e) Toluene has a solubility in water of 0.67g/L; it is miscible with carbon tetrachloride. Draw a flow chart to show how you could use extraction to separate a mixture of 0.3 g each of benzoic acid and toluene in 100 mL of carbon tetrachloride. Scheme 1
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Extractionworkshopkey - Chemistry 14CL Extraction Workshop...

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