Required Practical 6: 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 should you do before continuing with the chromatography video?

  Watch the previous video on atomic structure
• What is the sample of food coloring referred to in the experiment?

  U for unknown
• How many known food colorings are used in the experiment?

  Four
• What is the first step in carrying out paper chromatography?

  Draw a horizontal pencil line
• How far from the bottom should the pencil line be drawn on the chromatography paper?

  Around 2 cm
• What should be the distance between the pencil spots on the chromatography paper?

  Equal spaces with 1 cm clear at each side
• What is used to apply the food colorings to the chromatography paper?

  A capillary tube
• Why is it important to keep the spots small on the chromatography paper?

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

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

  It acts as the solvent
• What must be ensured about the pencil line during the chromatography process?

  It must be above the water surface
• Why should the sides of the paper not touch the beaker walls?

  It interferes with water movement
• What is usually placed on the beaker during chromatography?

  A lid
• What happens to the water during the chromatography process?

  It moves up the paper
• When should the chromatography paper be removed from the beaker?

  When the water has traveled 3/4 up
• What should be marked on the paper after removing it from the beaker?

  The point where the water reached
• What does the separation of the unknown color into three spots indicate?

  It is a mixture of three colors
• How can the identity of the unknown color be determined?

  By comparing spots with known colors
• What does the absence of color B in the unknown indicate?

  It does not contain color B
• What is the first step to calculate the RF value?

  Measure the distance from the pencil line
• How is the RF value calculated?

  Divide distance moved by chemical by solvent
• What is the RF value for the chemical in color A?

  0.2
• Do RF values have units?


  No, they do not have a unit
• What should be done if multiple chemicals have the same RF value?

  Repeat the experiment with a different solvent
• What if the chemical has never been analyzed before?

  Further analysis is needed to identify it
• Where can students find questions on this required practical?

  In the vision workbook
• What are the steps for carrying out paper chromatography?

  1. Draw a horizontal pencil line on chromatography paper.
  2. Mark pencil spots for known and unknown colors.
  3. Apply small spots of color using a capillary tube.
  4. Pour 1 cm of water into a beaker as solvent.
  5. Attach paper to a glass rod and lower into the beaker.
  6. Ensure the pencil line is above water and sides don't touch the beaker.
  7. Cover the beaker to reduce evaporation.
  8. Remove paper when water reaches 3/4 up.
  9. Mark the water level and hang the paper to dry.
• What are the key points to remember during chromatography?

  • Pencil line must be above water.
  • Sides of paper must not touch beaker walls.
  • Use a lid to reduce solvent evaporation.
• What is the process for identifying chemicals using RF values?

  1. Measure distance from pencil line to spot center.
  2. Measure distance moved by solvent.
  3. Calculate RF value by dividing distances.
  4. Compare RF value with a database.
  5. Repeat with different solvents if necessary.