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April 20, 2014

Homework Help: Sample purity

Posted by Sheryl on Sunday, October 15, 2006 at 4:16pm.

Question: A student spots an unknown sample on a TLC plate and develops it in pentane solvent. Only one spot, for which the Rf value is 0.05, is observed. Is the unknown a pure compound? What can be done to verify the purity of the sample using TLC?

My answer: It's not possible to tell if the sample is pure. The low Rf value indicates that the sample barely moved up the plate so more than one polar substance could well be sticking to the SiO2. A more polar solvent needs to be use to allow give the sample an opportunity to move up the plate and possibly separate. Purity will be verified if there is no separation.

Please check my answer.

Sheryl


That sounds ok to me.


how would you determine the degree of purity of a sample of sodium thiosulphate?

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