Chromatography

• What is the purpose of paper chromatography?

  To identify substances
• Why is it essential to learn the details of paper chromatography?

  It is a required practical
• What is labeled as U in the experiment?

  A sample of unknown food coloring
• What do the labels A to D represent in the experiment?

  Known food colorings
• How far from the bottom should the pencil line be drawn on chromatography paper?

  2 cm
• Why should the spots of food coloring be kept small?

  To prevent colors from spreading into each other
• What is the depth of water used in the beaker?

  1 cm
• What role does water play in the chromatography process?

  It acts as the solvent
• What happens if the pencil line touches the water?

  The ink will wash off the line
• Why do we put a lid on the beaker during chromatography?

  To reduce evaporation of the solvent
• When should the chromatography paper be removed from the beaker?

  When the water has traveled 3/4 up
• What does it indicate if the unknown color separates into three spots?

  It is a mixture of three colors
• How can we determine which known colors are in the unknown sample?

  By comparing the spots' alignment
• What does the RF value represent in chromatography?

  The ratio of distances moved by chemical and solvent
• How do you calculate the RF value?

  Distance moved by chemical / distance moved by solvent
• What is the RF value for color A if the chemical moves 14 mm and the solvent moves 70 mm?

  0.2
• Why might multiple chemicals have the same RF value?

  Different chemicals can have similar properties
• What should you do if a chemical has never been analyzed before?

  Conduct further analysis to identify it
• What are the steps for carrying out paper chromatography?

  1. Draw a pencil line on chromatography paper.
  2. Mark spots for known and unknown colors.
  3. Apply small spots of food coloring.
  4. Pour water into a beaker as solvent.
  5. Attach paper to a glass rod and lower it into the beaker.
  6. Ensure the pencil line is above water.
  7. Remove paper when water reaches 3/4 up.
  8. Mark the water level and hang to dry.
• What are the key points to remember during chromatography?

  • Pencil line must be above water.
  • Paper sides must not touch beaker walls.
  • Lid should be placed on the beaker to reduce evaporation.
• What are the limitations of RF values in chromatography?

  • Multiple chemicals can share the same RF value.
  • New chemicals may lack RF values in databases.
  • Further analysis may be needed for identification.