Lect. 9. solvent extraction

Solvent Extraction, Nernst Distribution law, Types of solvent extraction and its applications

1. Dr. Y. S. THAKARE M.Sc. (CHE) Ph D, NET, SET Assistant Professor in Chemistry, Shri Shivaji Science College, Amravati Email: [email protected] B Sc - II Year SEM-III PAPER-III PHYSICAL CHEMISTRY UNIT- V - PHASE EQUILIBRIUM Topic- Application of Nernst Distribution Law Solvent Extraction 25-September -20 1

2. Extraction The most important application of distribution law in industry as well as laboratory is the extraction. Extraction ( removal by a solvent) of an organic substance from an aqueous solution. The process is carried by shaking the aqueous solution with a immiscible organic solvent, say ether in a separating funnel . The distribution ratio of most of the organic compounds is very large in favour of organic solvents. On standing, the aqueous and ether layers separate in the funnel. Ether layer is separated and applied to distillation. The organic substance remains as residue in the flask.

3. Solvent Extraction Solvent extraction and is a method to separate compounds based on their relative solubilities in two immiscible liquids, usually water and an organic solvent. 19-September -20 19-September -20

4. EXTRACTION Simple Extraction Multiple Extraction There are two types of extraction 19-September -20

5. Simple Extraction: The extraction process when carried out with the total amount of given organic solvent in a single step is known as simple extraction.

6. Multiple Extraction: When the extraction is carried out in more number of steps by using small amounts of organic solvent from total solvent with same aqueous solution is known as multiple extraction. Multiple extraction gives more extraction of organic substance than single step extraction by using same amount of extracting solvent.

7. Equation for the solute left unextracted after n th extraction Suppose V ml of an aqueous solution contain ‘W’ kg of an organic substance. Let V 1 ml of given organic solvent is used for extraction in each step . Volume of aqueous phase =V mL Volume of organic phase =V 1 mL W kg

8. First extraction : Consider ‘x 1 ’ kg be the substance left unextracted in aqueous solution in the first operation.  Concentration in aqueous layer = and concentration in organic solvent =   Volume of aqueous phase =V mL Volume of organic phase =V 1 mL X 1 kg W-X 1 kg

9. From distribution law OR …..(1)  

10. Second extraction : Second extraction is carried by using same V 1 ml of fresh solvent from aqueous solution remained after first extraction. Let ‘x 2 ’ kg be the substance unextracted in aqueous layer.  Concentration in aqueous layer = and concentration in organic solvent =   Volume of aqueous phase =V mL Volume of organic phase =V 1 mL X 2 kg X 1 –X 2 kg

11. From distribution law OR ………(2) …..(3)  

12. 3) n th extraction : Similar to 2 nd extraction, n-extractions are carried out. Let ‘ x n ’ kg be the solute unextracted, then we get, ………(4)