Chromatography

• What does Paper Chromatography allow us to do

  Separate substances based on their different solubilities
• Give a quick summary of how you do chromatography(Not full Pratical)

  1)Get chromatography paper

  2)Draw pencil line near bottom

  3)Place dot for colours you have on line

  4)Place bottom of paper into a solvent(Liquid that dissolves substances)

  5)Solvent moves up paper and dissolves ink dots, which are then carried up the paper
• The paper in chromatography is in which phase and why

  Stationary phase because it does not move
• What phase do we call the solvent and why

  The mobile phase because it does move
• A pure compound will produce

  A single spot in all solvents
• The compounds in a mixture may separate into

  Different spots depending on the solvent
• A ink spot that travels further up the paper is

  More soluble
• An impure substance produces how many spots in paper

  2 or more spots
• Why do we draw our starting line in pencil

  The pen ink would move up the paper with the solvent
• what is the result of chromatography called

  Chromatogram
• What is an Rf value

  
  

  Is a ratio between the distance travelled by the dissolved substance(solute) and the distance travelled by the solvent
• How to calculate Rr Value

  Distance travelled by the Substance/ Distance travelled by the Solvent

  
  

  Make to when measuring substance we measure up to the centre
• How do you use paper chromatography to identify an unknown substance

  1)Placs dot of unknow chemical and place paper into solvent

  2)Wait for chemical to move

  3)Measure distance of unknow chemical From base line to chemical

  4)Measure the distance of solvent from baseline to solvent

  5)Find the Rf value from formula

  5)Compare value in data base to find identify of substance

  6)Several different substances could have the same Rf. we might have to repeat using a different solvent
• What happens if the value of Rf from unknown chemical has same value of several substances

  Repeat with different solvent
• What happens if unknown substance has never been analysed before

  There will be no Rf value on database so need to carry out further analysis