Answer to Question #120660 in Inorganic Chemistry for Rosa

Question

The partition coefficient of a base B (monoacidic) at a particular pH, in an octanol-water mixture is 1.45. Consider an experiment where 3.5 g of B are shaken with 100 mL of octanol and 50 mL of water.
Molar mass of B = 101.19 g mol-1

(i) Calculate the mass of B in the aqueous layer after shaking.

Answer 1

n_B = 3.5/101.19 = 0.035 mol ; n_{in octaniol} = x mol; n_{in water} = 0.035 - x mol

C_{in water} = (0.035 - x)/0.050 mol/L

C_{in octanol} = x/0.100 mol/L

K_D = C_{in octanol}/C_{in water}

1.45 = x*0.050/((0.035 - x)*0.100)

x = 0.026 mol

n_{in water} = 0.035 - 0.026 = 0.0090 mol

m_{in water} = 0.0090*101.19 = 0.91 g