Partition Coefficient and Retardation Factor

[java22]

Homework Statement

Homework Equations

R_d = retardation factor = (1 + (ƥ_bK_d / n))

log(K_oc) = -0.55logS + 3.64

K_d = K_oc*f_oc

The Attempt at a Solution

Part C is the only part I feel sure on. I simply plugged 1480 mg/L into the log(K_oc) equation above to solve for K_oc. Then I multiplied K_oc by the f_oc given in the problem statement to obtain K_d. Finally, I plugged K_d in the R_d 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 R_d of solute A so that I could plug in and solve for K_d, then use that K_d for the solute B to solve for its R_d. However, plugging in 1 for R_d gives a K_d 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 R_d 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 R_d 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 R_d?

 

[NascentOxygen]

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.

This is not my area, but your approach here does seem to accord with http://www.ufaventures.com/ufa_ventures/tech_briefs/chem_retard.html