Hypothesis: The purple food colouring from three different brands of purple coloured candies do not contain the same dyes Aim: To separate the dyes from three different brands of purple coloured candies using paper chromatography and compare the results obtained.
Apparatus and Materials: Four identical boiling tubes with stoppers and hooks, water, measuring cylinder, chromatography or newsprint, three different brands (A,B,C) of purple coloured candies Method:
1.Cut three pieces of chromatography paper/ newsprint 2cm x 8cm
2. Draw a line 1.5cm from one end of each piece of paper
3. Using one piece of paper for each brand of purple food colouring, put ne spot of the same size in the middle of the line drawn.
4. Measure the volume of water needed to reach about a quarter the height of the boiling tube Pour this Volume into each tube. Label the tubes A,B,C to match the brands.
5. Set up the investigations as shown in the diagram.
6. When the water reaches the top of the strips, remove each chromatogram and allow it to dry
7. Note the colours and positions of the spots Expected Results : The purple food colouring will separate into a number of colours each of which will form a spot at different positions in the chromatogram. If the colour of the spots and their positions are the same for each brand then the hypothesis is true and accepted.
Limitations/ Sources of error: If newsprint is used instead of chromatography paper, the spots may not separate completely. The spots of food colouring may not have been exactly the same size. Assumptions: Water is an efficient solvent for the different brands of purple food colouring.
