5.0 mmol of benzoic acid is dissolved in 50.0 mL of water, and then washed with

Question

5.0 mmol of benzoic acid is dissolved in 50.0 mL of water, and then washed with 20.0 mL of dichloromethane. After extraction, 0.88 mmol of benzoic acid was left in the water layer. What is the partition coefficient of benzoic acid for this setup?

Using the information from our previous extraction —extracting 5.0 mmol benzoic acid into 20.0 mL of dichloromethane from 50.0 mL of water— determine how many moles of benzoic acid remain in the aqueous layer after 2 extractions with 20.0 mL of dicholoromethane.

Explanation / Answer

Partition coefficient= Concentration of the compound in Organic layer/concentration of the same compound in the aqueous layer

there is total of 5mmol of benzoic acid , out of which 0,88 mmol was there in the aqueous layer, rest is there in dichloromethane layer. mmol of benzoic acid in dichloromethane= 5-0.88=4.12 mmol= 4.12*10-3 moles

concentration = moles of benzoic acid in organic layer/20/ ( moles of benzoic acid in aqueous layer/50)

concentration of benzoic acid in organic layer= 4.12*10-3/20

Concentration of benzoic acid in water(aqueous layer)= 0.88*10-3/50

hence partition coefficinet= 4.12*10-3*50/(0.88*10-3*20)= 11.7

1st extraction is done with 20ml of dichloromethane. Let x= mill moles of Benzoic acid in organic layer, 5-x =millimoles of Benzoic acid in water latyer, expressing concentration in millimoles/liter or moles/liter in this problem does not change the calculations.

hence K=11.7= x/20/(5-x)/50

11.7= 50x/(100-20x)

11.7*(100-20x)= 50x

1170-234x=50x

284x=1170

x= 4.119mmol

after 1st extraction, 5-4.119 = 0.88 mmols of benzoic acid remain in the aqueous phase.

for the second extraction , let x' =mole of Benzoic acid in the organic phase

hence 11.7= x'/20/(0.88-x')/50

11.7= 50x'/(20*(0.88-x)

11.7= 50x'/(17,6-20x')

11.7*(17.6-20x')= 50x'

205.92-234x'=50x'

284x'=205.92

x'=205.92/284=0.725

hence mmoles of Benzoic acid in aqueous layer= 0.88-0.725= 0.155mmoles

Related Questions

Navigate

• Browse (All)
• Browse 5
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.