TLC: Separation Of Silica Gel

As we know, the TLC is a separation technique that has two phases: the stationary phase and mobile phase. The stationary phase is silica gel (SiO2) which is very polar compound, while the mobile phase is 0.5% acetic acid which has less polar. Also, as we know, the compound will rather to stay with stationary phase or travel with mobile phase depend on its polarity. The result show as that the polarity of the solvent is the key factor for the compound to travel with it or stay in stationary phase. The result show us that the Caffeine has more polarity than other compounds because it stays in stationary phase which has high polarity. In contrast, the Ibuprofen is less polar, because it travels with the solvent which is less polar also. Therefore,
the polarity of the solvent and of the plate is play and key role to determine which compound is travel and which is stay. Moreover, if we change the solvent (0.5% acetic acid) with another solvent that has more polarity than the silica gel; therefore, the compound that has high polarity, such as caffeine, will travel with the solvent that has more polarity than the silica gel.
Meanwhile, the compound that has less polarity or non-polar will stay with stationary phase. In this experiment, the Rf value is determined by the difference of polarity between stationary phase and mobile phase. Rf (Retention factor) is a ratio between the travel distance of the sample to the travel distance of the solvent. It consider the identity of the compound and can help in the determination of unknown sample by comparing the known Rf value with the Rf value of unknown sample. Depend on the result, the more polar compound like caffeine has small Rf value (average 0.12) because it didn’t travel with the solvent. The Acetaminophen are less polar than the caffeine but more polar than the Aspirin and Ibuprofen and has average Rf value (0.4). The Aspirin has more Rf value (average 0.55) than the Caffeine and the Acetaminophen because it is less polar and travel with the solvent. The ibuprofen has the bigger Rf value in this experiment (average 0.7) because it has the lower polarity than the other samples in the experiment, so it travels away with the
solvent. Also, we determined the ingredients of unknown mixture by comparing it to the known mixture. We determined it visually and determined it after calculating the Rf value for it and compare with the known Rf value. For unknown mixture number 7, it contains Caffeine and Aspirin because they have almost similar Rf values with the known compounds. Also, we compared it visually we can see a spot near the line which mean this compound didn’t travel and this information is same as the information of the Caffeine. Also for the Aspirin, we see it visually it travels with the solvent more than spot number 2 for the known compound and this information, after calculating the Rf value, is same as the Aspirin. The small difference in Rf values between the same samples is due to human error like add a big drop on the plate with make the spot very big or add many drops which will cause a big tail and it will cause a mistake during calculating the distance travel by compound