c10 chemical analysis Flashcards
when is chromatography used?
to seperate mixtures of soluble substances and it can give information to help identify substances
what does separation depend on?
the distribution of substances between the phases
what do pure compounds produce
a single spot
what phase is paper?
the stationary phase as it does not move
what phase is the solvent?
mobile phase because it moves
what chemicals won’t move very far?
chemicals strongly attracted to the stationary phase (paper) won’t move very far
what chemicals will move further up the paper?
chemicals that are only weakly attracted will move further up the paper
required practical:
what does the required practical of chromatography use?
-4 known food colourings which could contain (A-D)
-plus an unknown mixture
what can help identify the compound?
different compounds have different rf values in different solvents
what do you draw on the chromatography paper?
-use a ruler to draw a horizontal pencil line and plot specific spots at equal spaces (1cm apart)
how far should the pencil line be from the bottom of the paper?
around 2cm
what do you use to put small spot of food colouring onto pencil spots ?
capillary tube (thin glass tube)
what must the sides of the paper not touch?
the walls of the beaker
why should you use a lid on the beaker?
to reduce evaporation of the solvent
when should you remove the paper and what do you do next?
remove the paper when water travelled 3/4 up then finally hang paper to dry
