Chem Lab

Here are the flashcards written out in a normal format:

TLC and Column Chromatography Flashcards (40)

1. What is chromatography?

• A separation technique where compounds in a mixture move at different speeds based on their affinities to the stationary and mobile phases.

2. What is the stationary phase in TLC?

• A thin layer of silica or alumina spread on a support (glass or plastic).

3. What is the mobile phase in TLC?

• An organic solvent mixture that moves the compounds up the TLC plate by capillary action.

4. What is the stationary phase in column chromatography?

• Silica or alumina packed into a column.

5. What is the mobile phase in column chromatography?

• A liquid solvent that carries the compounds through the column by gravity.

6. What is the Rf value?

• The ratio of the distance the compound traveled to the distance the solvent front traveled.

7. How is the Rf value calculated?

• Rf = Distance traveled by compound / Distance traveled by solvent front.

8. What is the purpose of TLC?

• To check the purity of compounds, identify compounds based on Rf values, and monitor reaction progress.

9. What is the purpose of column chromatography?

• To purify large amounts of compounds.

10. What happens if the solvent level covers the spots on a TLC plate?

• The spots will dissolve into the solvent pool, ruining the experiment.

11. How should TLC plates be handled?

• By the edges to avoid contamination.

12. What is elution in column chromatography?

• The process of compounds being carried out of the column by the mobile phase.

13. Which elutes faster in column chromatography, ferrocene or acetylferrocene?

• Ferrocene elutes faster because it is less polar.

14. What are the typical solvents used in TLC and column chromatography?

• Heptane and ethyl acetate in TLC; heptane and methyl t-butyl ether in column chromatography.

15. Why does acetylferrocene elute slower than ferrocene?

• Because acetylferrocene is more polar, it has a higher affinity for the stationary phase.

16. What is capillary action in TLC?

• The process by which the mobile phase moves up the TLC plate.

17. What are some applications of TLC?

• Checking purity, identifying compounds, and monitoring reactions.

18. What is a preparative method in chromatography?

• A method used to isolate and purify significant amounts of compounds.

19. What does a single spot on a TLC plate indicate?

• That the sample is pure.

20. What does it mean if multiple spots appear on a TLC plate?

• That the sample is a mixture of compounds.

21. How does polarity affect elution in chromatography?

• Polar compounds interact more with the stationary phase, causing them to move more slowly.

22. What safety measures are needed when handling ferrocene and acetylferrocene?

• Wear gloves, avoid inhalation, and work in a fume hood.

23. Why is dichloromethane considered hazardous?

• It is harmful if inhaled and is a carcinogen.

24. What happens if a column dries out in column chromatography?

• The column may crack, leading to poor separation of compounds.

25. What is the role of alumina or silica in chromatography?

• It acts as a polar stationary phase to which compounds bind.

26. What is the role of the sand in a column chromatography setup?

• To prevent the mobile phase from disturbing the stationary phase.

27. What visual techniques are used to see compounds on a TLC plate?

• UV light or chemical reactions that make compounds visible.

28. What is the retardation factor (Rf)?

• The ratio of the distance a compound traveled to the distance the solvent front traveled.

29. How can TLC be used to monitor reaction progress?

• By spotting the reaction mixture on a TLC plate and observing the appearance of new spots.

30. What happens if too much sample is spotted on the TLC plate?

• The spots may overlap, making it difficult to interpret results.

31. What type of stationary phase is typically used in TLC?

• Silica or alumina.

32. How does solvent polarity affect separation in column chromatography?

• A more polar solvent will increase eluting power, causing compounds to move faster.

33. What happens if the solvent in TLC has too high of an eluting power?

• All the compounds will elute immediately, leading to no separation.

34. What is the difference between analytical and preparative chromatography?

• TLC is analytical (small scale), and column chromatography is preparative (large scale).

35. Why is alumina highly polar?

• Due to its oxygen atoms on the surface, making it highly polar.

36. What is the function of the mobile phase in column chromatography?

• It carries the sample through the stationary phase by gravity.

37. How does a compound with high affinity for the stationary phase behave?

• It will elute slower because it interacts more with the stationary phase.

38. Why is column chromatography considered preparative?

• Because it is used to isolate large amounts of compounds.

39. What are some common errors in TLC experiments?

• Using too much solvent, overloading the TLC plate, or letting the solvent cover the spots.

40. What are some applications of column chromatography?

• Isolation and purification of large amounts of compounds.

Gas Chromatography and Refractive Index Flashcards (25)

1. What is gas chromatography (GC)?

• A chromatographic technique used to separate and analyze compounds based on their volatility and polarity.

2. What is the mobile phase in GC?

• An inert gas (e.g., nitrogen or helium).

3. What is the stationary phase in GC?

• A non-volatile liquid coated onto an inert solid support.

4. What is retention time (Rt) in GC?

• The time between the injection of the sample and the detection of a compound.

5. How does boiling point affect retention time in GC?

• Lower boiling point compounds elute faster, resulting in shorter retention times.

6. What is the carrier gas in GC?

• An inert gas, typically nitrogen or helium, that carries the sample through the column.

7. What is the purpose of the GC detector?

• To detect and measure the compounds as they elute from the column.

8. What is a chromatogram?

• A plot showing the detector response versus time, with peaks representing different compounds.

9. How does polarity affect retention time in GC?

• Polar compounds have longer retention times due to stronger interactions with the stationary phase.

10. What is the purpose of gas chromatography?

• To separate, identify, and quantify volatile compounds in a mixture.

11. What compounds can be analyzed using GC?

• Volatile liquids, gases, and low molecular weight solids.

12. What safety precautions should be taken when using GC syringes?

• GC syringes are sharp and fragile; handle with care to avoid injury.

13. What happens if the injection port in GC is left too long?

• The liquid may volatilize and expand, shooting the plunger out.

14. What is the relationship between peak area and compound amount in GC?

• The area under each peak is proportional to the concentration of the compound.

15. What is the refractive index (RI)?

• A measure of how much the speed of light is reduced as it passes through a material.

16. How is RI used in analysis?

• To identify substances or determine the composition of mixtures.

17. What does a high retention time indicate?

• A compound spends more time in the stationary phase, usually indicating higher boiling points or polarity.

18. What is the purpose of the Abbe Refractometer?

• To measure the refractive index of liquids for analysis.

19. What kind of samples can GC analyze?

• Gases, volatile liquids, and low molecular weight solids.

20. What is the purpose of the carrier gas in GC?

• To carry the sample through the column and aid in separation.

21. How does column temperature affect retention time?

• Higher column temperatures decrease retention times but may reduce resolution.

22. How do you calculate percent composition from a chromatogram?

• By comparing the areas of the peaks and calculating the relative proportions.

23. What factors affect retention time in GC?

• Boiling point, polarity, carrier gas flow rate, and column temperature.

24. What are some common errors in GC experiments?

• Incorrect injection volumes, improper temperature settings, or misinterpretation of peaks.

25. What happens if the carrier gas flow rate is too fast in GC?

• Shorter retention times, but the resolution of the peaks may decrease.

These flashcards should cover all the necessary information you need to study for your exam on both experiments. Let me know if you need further clarification!