Chromatography is a technique used to separate mixture into its individual components.
This method is commonly used to test ink, food colouring, and other coloured substances. It is widely used in a crime scene investigation. There are several types of chromatography, but we will only discuss paper chromatography.
Activity 1: Food Colouring
Objective: to test mixture of colours in food colouring
1. Draw a line on a rectangular filter paper about 1.5 cm from the bottom by using pencil
2. Put one drop of each food colouring (red, blue and green) on the line by using toothpick
3. Pour 20 ml distilled water into the beaker
4. Dip the filter paper in the beaker and hang it by using toothpick
5. Make sure the pencil line is above the water level.
6. Wait 10-15 minutes
7. Record your observations.
Results & Observation:
Red colour shows slightly orange at the top
Blue colour shows slightly purple
Green colour separates into blue and yellow
Discussion & conclusion:
Red food colouring shows the purest red colour, while green colour is a mixture.
Activity 2: Permanent marker
The steps are the same with Activity 1, only change the food colouring to marker.
We use 3 different colours (red, blue and black) from 3 different brands of markers.
From the results, the ink which traveled the highest is the most soluble in water.
Oppositely, the lowest distance traveled by the ink shows the ink is less soluble in water. So, buy that brand. You don’t want your writing easily wash away if it comes in contact with water, do you?
As for the mixture of colours, you have to test for yourself, as different marker gives different result. You may be surprise with the result.
Activity 3: Detective Play
I ask the students to draw a group symbol. It is hidden from other groups.
Each of the symbols is then put into an envelope.
Next, one group take one envelope (make sure they don’t get their own).
Now, they have to find out the owner of the symbol by testing the ink of the marker used.
The students get the sample ink from the note. They use the chromatography technique.
The result is then compared to the ink results from previous activity.
They should be able to find out the brand of the marker used and then name which group owns the symbol.
Out of 6 groups, 4 groups of students are able to state the correct owner of the symbol.
The fastest group with the correct answer is the winner.
Download the materials: