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.

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.

To know well about this lab on weigh 20grams soil sample in a breaker

To calculate the partition coefficient (Kd) for this chemical on the soil, we need to convert the concentrations to the same unit of measure.

Given information:
Soil mass = 20 g
Water volume = 500 mL

Concentration in soil = 100 mg/kg
Concentration in water = 250 µg/L

1 kg = 1000 g (Conversion factor for mass)
1 L = 1000 mL (Conversion factor for volume)

Converting the concentration in the soil to µg/L:
1 mg/kg = 1 µg/g (Conversion factor for mass)
100 mg/kg = 100 µg/g = 100 µg/1000 mL = 0.1 µg/mL = 0.1 µg/L

Now, we can calculate the partition coefficient (Kd):

Kd = (Concentration in soil)/(Concentration in water)
= 0.1 µg/L / 250 µg/L
= 0.0004

Therefore, the partition coefficient for this chemical on this soil is 0.0004.

To calculate the partition coefficient, we need to determine the concentration of the chemical in both the soil and the water.

First, we need to convert the concentration of the chemical in the soil from mg/kg to µg/g (since the partition coefficient is usually expressed in terms of µg/g).

Given that the concentration of the chemical in the soil is 100 mg/kg, we need to convert this to µg/g by multiplying it by 1000:
Concentration in soil = 100 mg/kg * 1000 µg/mg = 100000 µg/kg

Next, we need to convert the concentration of the chemical in the water from µg/L to µg/g. Since 1 L of water weighs 1000 g, we can convert the concentration by dividing it by the density (mass/volume) of the water at equilibrium.

Given that the concentration of the chemical in water is 250 µg/L, we can calculate the concentration i using the following steps:

1. Convert volume of water from mL to L:
Volume of water = 500 mL * (1 L/1000 mL) = 0.5 L

2. Calculate concentration i:
Concentration in water = 250 µg/L / 0.5 L = 500 µg/g

Now that we have the concentration of the chemical in both the soil and the water, we can calculate the partition coefficient:

Partition coefficient = Concentration in soil / Concentration in water
Partition coefficient = 100000 µg/kg / 500 µg/g

To get the partition coefficient in the same units, we need to convert µg/kg to µg/g. Since 1 kg = 1000 g, we can convert the units by dividing by 1000:

Partition coefficient = 100000 µg/g / (500 µg/g / 1000)
Partition coefficient = 100000 / 0.5

Therefore, the partition coefficient for this chemical on this soil is 200,000 µg/g.