How Would The Rf Values Change If A More Polar Solvent Were Used

True or False: A sample of aspirin has an $R_f$ value of 0.20 when measured on a silica gel TLC plate with a certain solvent mixture. If the polarity of the solvent is increased, the $R_f$ value of the aspirin will become larger.

Would this be false? Because aspirin is polar (I believe would be considered polar because it dissolves in water despite some other sources saying that it is actually non-polar) and the silica in the TLC plates are also polar, aspirin would not be able to travel very far because it would interact with the silica. Thus, shorter distance over longer distance = lower $R_f$ value, with $R_f$ = distance spot moves/ distance solvent moves.

You are watching: How would the rf values change if a more polar solvent were used

*

*

I wish we would stop teaching chromatography in terms of “polar” and “nonpolar.”

The aspirin will interact fairly strongly with the silica due to hydrogen bonding/electrostatic interactions of the carboxylic acid and the ester with the silica. If you increased the “polar” component of the mobile phase, it would travel further due to the mobile phase competing more for binding spots of the silica gel.

So increasing the polarity of the mobile phase does raise $mathrm{R_f}$ of aspirin (or anything) on regular silica gel.

*

Since aspirin has a carboxylic acid group on it, it would be considered polar. Silica gel, consisting of $ce{SiO2}$, is also polar. Since polar molecules attract other polar molecules, the aspirin molecules will tend to bind to the silica and not move up the TLC plate in a nonpolar eluent, resulting in a low $R_f$ value.

See more: Anatomical Crown Vs Clinical Crown, Anatomic Crown: What It Is & The 3 Layers

When the polarity of the eluent is increased, its ability to attract polar molecules is increased. This means that it can better compete with the silica in attracting the aspirin, and the $R_f$ value will be higher.

*

Thanks for contributing an answer to brianowens.tv Stack Exchange!

Please be sure to answer the question. Provide details and share your research!

But avoid

Asking for help, clarification, or responding to other answers.Making statements based on opinion; back them up with references or personal experience.

Use MathJax to format equations. MathJax reference.

See more: What Do You Call Someone From Honduras Called In Spanish? Like I&#39M American

To learn more, see our tips on writing great answers.

Post Your Answer Discard

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged polarity chromatography or ask your own question.

*

site design / logo © 2021 Stack Exchange Inc; user contributions licensed under cc by-sa. rev2021.9.10.40187

Your privacy

By clicking “Accept all cookies”, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy.

Published

Leave a comment

Your email address will not be published. Required fields are marked *