Practical 12

• Outline a method to separate a mixture using thin layer chromatography.

  > Take a silica plate and draw a horizontal pencil line 2 cm from the bottom

  > Wear gloves to prevent contaminants from your skin from going onto the plate

  > Using a fine glass spotter add one drop of the mixture on to the pencil line. Repeat this step, allowing the spot to dry to create a concentrated spot

  > Using another clean glass spotter, add drops of known substances on the pencil line
• Outline a method to separate a mixture using thin layer chromatography. pt2

  > Add a small amount of solvent to a beaker

  > Place the plate into the beaker ensuring the solvent is below the pencil line. Put a lid on the beaker to reduce solvent evaporation and create a saturated solvent atmosphere

  > Remove the plate from the beaker before the solvent reaches the top of the plate and mark the solvent front

  > Allow the solvent to dry and place the plate under a UV lamp or stain with iodine

  > Calculate the Rf value for each spot and compare the Rf values
• State if the following steps are essential and why:

  Using gloves or tweezers to handle the plate.

  > Yes, to prevent contaminants from your skin from going onto the plate

  Drawing a pencil line 1 cm from the bottom of the plate.

  > No, the pencil line does not have to be drawn 1 cm from the bottom

  Adding a lid to the beaker which contains the plate and the solvent.

  > Yes, to reduce solvent evaporation and also create a saturated solvent atmosphere

  Removing the plate when the solvent reaches 2 cm from the top of the plate.

  > No, the substances and solvent move at a relative rate
• If the spots are not visible on the chromatogram, what can be done to make them visible?

  > Place the plate under a UV lamp or stain with iodine
• Explain why substances in a mixture separate out using thin layer chromatography.

  > The substances have a different attraction to the stationary phase (silica) and the mobile phase (solvent). Substances also have a different solubility in the solvent.