A chemical is placed in a beaker containing 20 g of soil and 500 mL of water. At equilibrium, the chemical is found in the soil at a concentration of 100 mg/kg of soil. The equilibrium concentration of this same chemical in the water is 250 µg/L. Calculate the partition coefficient for this chemical on this soil.
chemistry - DrBob222, Saturday, January 22, 2011 at 12:20pm
I don't know what you've been told about the K but it can be written either K for organic layer/water layer or water layer/organic layer. The Ks I have seen USUALLY have been written as Korganic/aqueous.
Ko/a = mass organic phase/mass aq phase.
soil phase = organic phase = 100 mg/kg which is 100E-3g/1000g which is 0.0001 g/g. The problem states a 20 g soil sample was used; therefore, 0.0001*20 = 0.002 g chemical A in the soil (organic phase). For water, it is 250 ug/L which is 250E-6g/L and we took a 500 mL sample; therefore, chemical A in the water is 250E-6*0.5L = 0.000125 g. So Ko/a = 0.002/0.000125.
Check my work. Check my thinking.