Chromatography Practice Questions PDF

Questions: 1. What is the general principle behind all chromatographic techniques? * A) Separation of compounds based on their boiling points. * B) Separation of compounds based on their differential interactions with a stationary and a mobile phase. * C) Separation of compounds based on their dens...

Questions: 1. What is the general principle behind all chromatographic techniques? * A) Separation of compounds based on their boiling points. * B) Separation of compounds based on their differential interactions with a stationary and a mobile phase. * C) Separation of compounds based on their densities. * D) Separation of compounds based on their melting points. 2. In thin-layer chromatography (TLC), what is the stationary phase typically? * A) A liquid solvent. * B) A thin layer of silica gel or alumina on a glass or plastic plate. * C) A gas, such as nitrogen or helium. * D) A porous solid packed into a column. 3. In thin-layer chromatography (TLC), what is the mobile phase? * A) A solid adsorbent. * B) A liquid solvent. * C) A gas. * D) The sample mixture itself. 4. What is the purpose of a developing tank/chamber in TLC? * A) To heat the TLC plate * B) To create a saturated atmosphere of the solvent * C) To dry the TLC plate. * D) To apply the sample 5. How should a TLC plate be placed in the developing tank? * A) With the base line above the level of the solvent. * B) With the base line below the level of the solvent * C) Completely submerged in the solvent. * D) The solvent is not placed in a developing tank. 6. How are colourless spots typically visualised on a TLC plate? * A) By heating the plate. * B) By using a UV lamp or a locating agent (e.g., iodine vapour). * C) By adding water to the plate. * D) By looking at the plate under a microscope. 7. What does the Rf value represent in TLC? * A) The distance travelled by the solvent front. * B) The ratio of the distance travelled by a compound to the distance travelled by the solvent front. * C) The distance travelled by the sample spot. * D) The time taken for the separation. 8. What factors affect the Rf value of a compound in TLC? * A) The solvent used, the stationary phase, and the compound's polarity. * B) The size of the TLC plate. * C) The temperature of the room. * D) The concentration of the sample. 9. In column chromatography, how are compounds eluted (collected) from the column? * A) By heating the column. * B) By continuously passing a solvent through the column. * C) By applying a vacuum to the column. * D) By scraping the stationary phase out of the column. 10. In column chromatography, what is the stationary phase? * A) A liquid solvent * B) A solid adsorbent packed into a glass column * C) A gas * D) The sample mixture 11. In column chromatography, what is the mobile phase? * A) A liquid solvent * B) A solid adsorbent packed into a glass column * C) A gas * D) The sample mixture. 12. In gas chromatography (GC), what is the mobile phase? * A) A liquid solvent. * B) A solid adsorbent. * C) An inert carrier gas (e.g., helium, nitrogen). * D) The sample mixture itself. 13. In gas chromatography (GC), what property of the compounds primarily determines their separation? * A) Their melting points. * B) Their boiling points and their interaction with the stationary phase. * C) Their densities. * D) Their colour. 14. What is the stationary phase in gas chromatography? * A) A high boiling point liquid adsorbed onto an inert solid support. * B) A solid adsorbent. * C) A gas. * D) The sample itself. 15. What is the purpose of the detector in gas chromatography? * A) To vaporise the sample. * B) To separate the components of the sample. * C) To detect the separated compounds as they elute from the column. * D) To control the temperature of the column. Answers and Explanations: 1. B - All chromatography relies on differences in how compounds distribute themselves between a stationary and a mobile phase. 2. B - Silica gel (SiO2) and alumina (Al2O3) are common stationary phases. 3. B - A suitable liquid solvent carries the sample mixture up the plate. 4. B 5. A 6. B - UV light or chemical stains (locating agents) make the spots visible. 7. B - Rf = (distance moved by compound) / (distance moved by solvent) 8. A - Polarity is a key factor in how strongly a compound interacts with the stationary and mobile phases. 9. B - The solvent (eluent) carries the separated compounds out of the column. 10. B 11. A 12. C - An inert gas carries the vaporized sample through the column. 13. B - Compounds with lower boiling points tend to travel faster through the column. Interactions with the stationary phase also play a role. 14. A 15. C - The detector senses the presence of each compound as it leaves the column, generating a signal.