chromatography

    Subdecks (1)

    Cards (24)

    • what is chromatography used for
      to separate mixtures and can give information to help identify substances
    • what are mixtures separated by
      their solubility (how well a substance in a mixture dissolves in the solvent)
    • set up of chromatography
      .
    • during set up for chromatography why should we use pencil for the baseline rather than pen
      pen would dissolve in the solvent and move up the paper
    • what is the name given for the pencil line in paper chromatography
      base line
    • what are the two of phases chromatography
      stationary phase
      mobile phase
    • what is the mobile phase
      substance molecules can move in (e.g. liquid/gas)
    • what is the stationary phase
      substance molecules can't move in (e.g. solid thick liquid)
    • do substances in the sample remain at one phase through the whole investigation
      no, the will constantly shift between the two
    • how does the distance travelled by the substance determine how soluble it is
      the solutions travelling further up the paper means it was more attracted to the solvent (more soluble) and therefore spent more time in the mobile phase - which makes the solution move faster
      the solutions which remained closer to the start suggests that they were more attracted to the paper (less soluble) and therefore spent more time in the stationary phase - which makes the solution move slower
    • example of a pure compound in chromatography
      a pure compound will produce a single spot in all solvents
    • example of an impure mixture in chromatography
      the compounds in a mixture will separate into many different spots
    • what does the RF value show
      the ratio of the distance moved by a compound (centre of spot from origin) to the distance moved by the solvent 
    • calculating RF value
      measure the distance travelled by the solvent and each substance
      1. 1.5/9.7 = 0.15
      2. 3.7/9.7 = 0.38
      3. 8.2/9.7 = 0.85
    • why are no units needed
      as the ratio cancels out the units
    • what does a higher RF value mean
      the further up the chromatography paper the substance travelled