Question

Which of the following statements regarding thin layer chromatography are TRUE? In thin layer chromatography, a polar organic compound will be repelled by the adsorbent and therefore travel not as far up the plate than a non-polar compound In thin layer chromatography, a polar organic compound will be attracted by the adsorbent and therefore travel not as far up the plate as a non-polar compound Sample spots should be approximately 1 cm in diameter. Covering the sample jar is done to prevent fingerprints on the slide. The Rf value will change if the adsorbent material is changed. Thin layer chromatography is an example of adsorption chromatography, and not partition chromatography.

Answer 1

In thin layer chromatography, a polar organic compound is attracted to the polar stationary phase and moves less up the plate than a non-polar compound. Sample spots should be small, and covering the jar maintains solvent vapors, not to prevent fingerprints. TLC is adsorption chromatography, and the Rf value changes with different adsorbents.

Step-by-step explanation:

In thin layer chromatography (TLC), the interaction between the stationary phase and the compounds of interest is crucial for separation. A polar organic compound will be attracted by the adsorbent (usually a polar substance like silica gel) and, therefore, will travel not as far up the plate as a non-polar compound. This is because the polar compound forms stronger interactions with the polar stationary phase, causing it to move slowly within the mobile phase and have a lower Rf value.

Sample spots should not be large, ideally much less than 1 cm in diameter, to ensure a good resolution in the separation process. The common practice of covering the sample jar is actually to maintain a saturated environment of the solvent vapors, ensuring uniform development of the chromatogram, rather than to prevent fingerprints. Lastly, changing the adsorbent material will indeed change the Rf value for the compounds being separated because the interaction strength between the new adsorbent and each compound may vary significantly compared to the original adsorbent.

TLC is indeed an example of adsorption chromatography, which relies on the adsorption of substances to the stationary phase, unlike partition chromatography, where separation is based on the differential solubility of compounds between two immiscible phases.

Answer 2

a) False

b) True

c) False

d) False

e) True

f) True

Step-by-step explanation:

a) In thin layer chromatography, a polar organic compound will be repelled by the adsorbent and therefore travel not as far up the plate than a non-polar compound. FALSE. The adsorbent usually is a polar compound that will attract the polar organic compound.

b) In thin layer chromatography, a polar organic compound will be attracted by the adsorbent and therefore travel not as far up the plate as a non-polar compound. TRUE. The polar organic compound will be attracted by the adsorbent doing its travel not as far.

c) Sample spots should be approximately 1 cm in diameter. FALSE. Sample spots must be of 1-2 mm of diameter.

d) Covering the sample jar is done to prevent fingerprints on the slide. FALSE. The covering is doing to saturate the jar's air with solvent.

e) The Rf value will change if the adsorbent material is changed. TRUE. The travel of the compound depends of the retention that is made by the adsorbent material.

f) Thin layer chromatography is an example of adsorption chromatography, and not partition chromatography. TRUE. The mechanism of separation in thin-layer chromatography is differences of adsorption from different compounds.