Attached tile question in your pout-lab What it mean if two substances are run o
ID: 959622 • Letter: A
Question
Attached tile question in your pout-lab What it mean if two substances are run on the same TLC plate and are found to have the same R_f value Why do you use a pencil and not a pen to mark the TLC plates? Consider the following silica gel TLC plate of compounds A, B, and C. The plate was developed in hexanes. While using a ruler measure and calculate the R_f values of compounds A and B run on a silica gel TLC plate using hexanes as the solvent. Which compound between A and B is the most polar? An unknown compound C was eluted with hexane on different spots with A and B as shown. What can you say about unknown C based on the R_f values.Explanation / Answer
1. If the two compounds run on the TLC have same Rf values then the two compounds are said to be same (not always)
2. Because ink may dissolve in the solvent. A pencil mark is made of graphite which is not soluble in anything.
3.a. The retention factor, or Rf, is defined as the distance traveled by the compound divided by the distance traveled by the solvent.
for A, Rf = 3.5cm/4cm = 0.875 means less polar
for B, Rf = 2.5cm/4cm = 0.625 means more polar
b. Compound A with the larger Rf is less polar because it interacts less strongly with the polar adsorbent on the TLC plate.
c. compound c showing spots equal to compounds A and B hence it may be a mixture of A&B
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