Question

You want to decaffeinate your coffee by extracting the caffeine outwith dichloromethane. It's too late to extract the caffeinefrom the coffee beans because you've already brewed yourself a 200mL cup of coffee. Your particular brand of coffee contains100 mg of caffeine in that 200mL cup. The partitioncoefficient of caffeine in dichloromethane/water is 9.0. How much caffeine would still be in your 200 mL if you did: A. One extraction using 200 mL ofdichloromethane B. Two extractions using 100 mL ofdichloromethan each. Please show all steps! Thank you!

Answer 1

Dear friend

                                                                       [g/100 mL] in organic phase

                        Partition coefficient (K) =         ----------------------------------------------------

                                                                       [g/100 mL] in aqueous phase

The partition coefficient of caffeine in dichloromethane/water is 9.0. it means for every 100 mL 90 mg caffeine goes into dichloromethane and 10 mg goes into water.

A. One extraction using 200 mL of dichloromethane ------   10 mg remains because 90 mg goes into 200 mL dichloromethane

B. Two extractions using 100 mL of dichloromethan each ------    nothing remains because first 100 mL takes 90 mg then next 100 mL takes 10 mg into dichloromethane.

Thank you.