Composition of Inks

• Describe how to separate soluble coloured substances.

  Chromatography, place a spot of the sample on a pencil line on a piece of chromatography paper. Place the paper in a beaker of solvent below the pencil line, remove from the solvent and leave to dry once the solvent has travelled up 2/3 of the paper.
• Why are in spots place above the level of the solvent in the beaker?

  If they were below the solvent level the ink would dissolve in the solvent rather than moving up the chromatography paper.
• What is meant by a ‘solvent front’?

  The furthest distance reached by the solvent.
• How can you use chromatography to see if a certain substance is present in a mixture?

  Run a pure sample of this substance alongside the unknown mixture, if the Rf value of the pure substance matches the value of one of the spots from the mixture it is likely to be present.
• Why should chromatography paper be removed form the solvent before the solvent front reaches the top?

  To allow the distance moved by the solvent to be measured so that the Rf value can be calculated.
• What are the 2 phases in chromatography?

  Mobile phase - solvent which carries substances up the stationary phase.

  Stationary phase - paper or thin layer of inert substance on a glass plate.
• How do you calculate the Rf value?

  Distance travelled by substance / distance travelled by solvent, the Rf value is always between 0 and 1
• In paper chromatography, what is the stationary phase?


  The chromatography paper.
• In paper chromatography, what is the mobile phase?


  The solvent, e.g. water or ethanol
• Describe how to obtain a sample of pure water from ink.

  Simple distillation: gently heat the ink in a round bottomed flask using a Bunsen burner, the water from the ink evaporates then cools in the condenser, the pure water is collected in a beaker.
• How do you set up a condenser for simple distillation?

  The condenser should be horizontal with water in at the bottom and water out at the top.
• When using simple distillation to collect pure water, what temperature will be on the thermometer?

  100 degrees Celsius
• Precautions when using a Bunsen burner.

  Don’t leave unattended, turn of gas or leave on orange safety flame when not in use, tie back long hair, work in a clear space, move any flammable substances away.
• Precautions when handling harmful solvents.

  Wear gloves and safety goggles, use in a well ventilated lab or use a fume cupboard, clean up any spillages.