Question: Consider a sample that is a mixture composed of biphenyl, benzoic acid and benzyl alcohol. The sample is spotted on a TLC plate and developed in a dichloromethane-cyclobutane solvent mixture. Predict the relative Rf values for the three components in the mixture. (Hint: See Table 19.3 which gives elution sequence for compounds.)
My answer: I understand the order of Rf values and speed of travel. Seems like a guesstimate is in order as I'm not given any information about specific values. How about: Benzoic acid Rf about = .25; benzyl alcohol about = .50; biphenyl Rf about = .90.
Your answers are very helpful in pointing out my incorrect ways of evaluating the questions.
Sheryl
Rf value defined as the distance travelled by the elute divided by the distance travelled by the solvent
Rf value defined as the distance travelled by the elute divided by the distance travelled by the solvent
Rf value defined as the distance travelled by the elute divided by the distance travelled by the solvent
In this case, the relative Rf values for the three components in the mixture can be determined by looking at the elution sequence for the compounds in Table 19.3. Benzoic acid would have the lowest Rf value, followed by benzyl alcohol, and then biphenyl with the highest Rf value.
I'm glad you found my previous answers helpful! However, in this case, I can provide you with a more accurate prediction of the relative Rf values for the three components in the mixture.
According to the hint, Table 19.3 provides the elution sequence for compounds. Since biphenyl is nonpolar and usually elutes first, it would have the highest Rf value. Benzoic acid, being a polar compound, will have a lower Rf value compared to biphenyl. Benzyl alcohol, also being polar, will have a lower Rf value compared to both biphenyl and benzoic acid.
Based on this information, a more accurate prediction for the relative Rf values in the mixture would be:
Biphenyl: Rf value ~ 0.90
Benzyl alcohol: Rf value ~ 0.50
Benzoic acid: Rf value ~ 0.25
Keep in mind that these values are estimates and can vary depending on the specific conditions of the TLC experiment.
To predict the relative Rf values for the three components in the mixture, you can refer to Table 19.3 in your source material, which provides the elution sequence for compounds. The elution sequence indicates the order in which different compounds move on a TLC plate.
Based on the information provided and using Table 19.3 as a reference, here is one possible way to estimate the relative Rf values for biphenyl, benzoic acid, and benzyl alcohol:
1. Biphenyl: Since it is a non-polar compound, it will likely have a higher affinity for the non-polar solvent (dichloromethane) and will thus have a higher Rf value. You can estimate its Rf value to be around 0.90.
2. Benzyl alcohol: This compound is slightly polar due to the presence of the alcohol group. It will have some affinity for the polar solvent (cyclobutane) in the mixture but less than biphenyl. As a result, you can estimate its Rf value to be lower than biphenyl, perhaps around 0.50.
3. Benzoic acid: This compound is more polar than benzyl alcohol due to the presence of the carboxylic acid functional group. It will have a higher affinity for the polar solvent and will likely have the lowest Rf value among the three compounds. You can estimate its Rf value to be around 0.25.
Remember, these estimates are based on the general trends in polarity for the compounds and the given solvent mixture. The actual Rf values may vary depending on the specific conditions of the TLC experiment.
It's important to note that without more specific experimental data, these estimates are simply educated guesses. Performing an actual TLC experiment and comparing the spots to known standards would provide more accurate and reliable Rf values for the components in the mixture.