Partition Coefficient and Retardation Factor

In summary: The partition coefficient, Kd, is the fraction of a solute that is partitioned between the aqueous phase and the solid phase."
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Homework Statement



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Homework Equations



Rd = retardation factor = (1 + (ƥbKd / n))

log(Koc) = -0.55logS + 3.64

Kd = Koc*foc

The Attempt at a Solution



Part C is the only part I feel sure on. I simply plugged 1480 mg/L into the log(Koc) equation above to solve for Koc. Then I multiplied Koc by the foc given in the problem statement to obtain Kd. Finally, I plugged Kd in the Rd equation above along with the bulk density of the soil and the soil porosity given, and solved. Seems straight forward enough.

Part A is simply a concept-type question, but I do not know how to relate coefficients to this type of graph shown. Since there is no textbook for the class, I have no way to confirm if I'm right or not in my current thinking. I answered that the partition coefficient would be biggest for solute C and smallest for solute A, because a small partition coefficient would imply it dissolves in water more easily, shown by the graph for solute A reaching equilibrium the quickest. Am I correct here?

Part B is the oddest for me. At first I thought it was giving me the Rd of solute A so that I could plug in and solve for Kd, then use that Kd for the solute B to solve for its Rd. However, plugging in 1 for Rd gives a Kd of 0, so it must not be the right method. So, I simply compared the times it took solute A and solute B, and multiplied solute A's Rd by the same factor. So since 3.5 hours is 1.75x more than 2 hours, I did (1 * 1.75) = 1.75 for the Rd of solute B. I'm sure this method is totally wrong, but I have no references to find the right way, so any help would be much appreciated.

One thing that immediately let's me know I'm wrong somewhere is that I never used the 20 cm length given in the problem statement. Is this somehow used to find solute B's Rd?
 
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  • #2

1. What is the difference between partition coefficient and retardation factor?

The partition coefficient (K) measures the distribution of a solute between two immiscible phases, such as a solid and liquid. It is defined as the ratio of the solute concentration in one phase to its concentration in the other phase. On the other hand, the retardation factor (R) is a measure of a solute's mobility in a porous medium, such as soil or rock, relative to the flow of water. It is calculated by dividing the velocity of the solute by the velocity of the water.

2. How are partition coefficient and retardation factor related?

Partition coefficient and retardation factor are related by the equation R = 1 + (Kf/n), where K is the partition coefficient, f is the porosity of the medium, and n is the degree of water saturation. This relationship shows that the retardation factor increases as the partition coefficient increases, indicating a stronger retention of the solute in the medium.

3. What factors influence the partition coefficient and retardation factor?

The partition coefficient is influenced by the chemical properties of the solute, such as its molecular weight, polarity, and solubility. It is also affected by the properties of the two phases, such as their polarity and temperature. The retardation factor is influenced by the properties of the porous medium, including its porosity, permeability, and surface area, as well as the properties of the solute and the flowing water.

4. How are partition coefficient and retardation factor used in environmental studies?

In environmental studies, partition coefficient and retardation factor are used to understand the fate and transport of contaminants in soil and groundwater. They can help determine the potential for a contaminant to leach into groundwater and the rate at which it will move through the subsurface. This information is important for assessing and managing environmental risks.

5. Are there any limitations to using partition coefficient and retardation factor?

While partition coefficient and retardation factor are valuable tools in environmental studies, there are some limitations to their use. Both measures assume equilibrium conditions, which may not always be the case in natural systems. They also do not take into account the effects of biodegradation, which can significantly impact the mobility of contaminants. Additionally, the accuracy of these measures may be affected by uncertainties in the data used to calculate them.

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