mixtures and chromatography

• why should you put a lid on the container during a paper chromatography experiment?

  a lid helps to stop the solvent from evaporating
• true or false? when substances are combined in a mixture, their chemical properties change.

  false. the chemical properties of the substances in a mixture are unchanged.
• what is a solvent front?

  the point that the solvent in paper chromatography reaches as it moves up the paper
• what is a mixture?

  a mixture consists of two or more elements or compounds that are combined, but not chemically bonded together.
• explain why techniques to separate mixtures are combined in a mixture, their chemical properties change.

  the separation of a mixture is a physical process because it does not involve any chemical reactions, and no new substances are made.
• Stephen is doing a a paper chromatography experiment. he uses a pen to draw a line near the bottom of the filter paper. why is this wrong?

  the line should be drawn in pencil - pen contains ink that will dissolve in the solvent
• explain how chromatography could be used to separate a mixture containing three different dyes

  put a dot of dye mixture on the pencil line and place the filter paper in solvent. each different dye in the mixture will move up the paper at a different rate, separating out the dyes. you will end up with three different spots on your chromatogram