A certain organic acid (A) was prepared by dissolving 3 g of A in 100 mL. of wat

Question

A certain organic acid (A) was prepared by dissolving 3 g of A in 100 mL. of water. The solubility of A in water is 3g/100 mL and solubility in an organic solvent (dichloromethane) is 6g/100 mL. An organic chemistry student was asked to extract compound A using on either on portion of 50 mL. dichloromethane or two 25mL. portions of dichloromethane. a) What is the mass of compound A that can be extracted using one 50 mL portion of the organ solvent? b) What is the mass of compound A that can be extracted using two 25 mL portions of the organic solvent?

Explanation / Answer

1. Distribution coefficient for A = 6/3 = 2

a) extraction with 50 ml organic solvent

2 = (x/50)/[(3 - x)/100]

0.06 - 0.02x = 0.02x

x = 0.06/0.04 = 1.5 g

so 1.5 g would be extracted with a 50 ml portion of organic solvent

b) first extraction with 25 ml

2 = (x/25)/[(3 - x)/100]

0.06 - 0.02x = 0.04x

x = 0.06/0.06 = 1 g

Second extraction

2 = (x/25)/[(2 - x)/100]

0.04 - 0.02x = 0.04x

x = 0.04/0.06 = 0.667 g

total mass of A extracted = 1.667 g

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