6. Show how mixtures can be separated using chromatography

Prior Learning: 

Use the previous lessons to recap on separation and mixtures before introducing chromatography. 

Starter

Introduce the topic of chromatography and its applications in separating mixtures by asking students what happens when ink runs.

Main Teaching

Explain that chromatography is a method used to separate mixtures based on the different properties of their components. Show a visual demonstration of chromatography, using food colouring in water as an example.

Activity (30 minutes):

• Provide each student with a filter paper, a petri dish or container and a marker pen.
• Instruct students to cut a piece of filter paper that fits into their container.
• Tell them to place the filter paper vertically into the container.
• Have students use the marker pen to make a single dot of colour at the bottom of the filter paper.
• Next, students will slowly add a solvent (water or alcohol) to the container, allowing it to rise up the filter paper.
• Observe and record the separation of the different pigments in the marker pen as the solvent reaches the top of the filter paper.
• Students can also compare the results obtained with different solvents.

Career Film: Harley Glover Newson is a Digital and Technical Solutions Degree Apprentice at Rolls-Royce. Harley explains why he opted for a career at Rolls Royce,

Expert Film: Dr Jason Owen from the James Hutton Institute demonstrates how chromatography can be used to separate mixtures.

Mission Assignment

CSI: Black Pen Investigation 

For this Mission Assignment, students should work in small groups and be given a selection of three fine liner/ felt tip pens. They should first  draw a line on a piece of filter paper in pencil, 1 cm from the bottom. 

One student should then make a small dot in the middle of the line on the filter paper using one of the black pens, keeping it secret from the others in their group.

They will now carry out a chromatography investigation to identify which pen was used. 

To do this they will need to set up three more pieces of filter paper like the first one and draw a dot using a different pen for each piece. 

The four pieces of filter paper can then be folded over the top of a splint each and secured in place with a paperclip. The papers should then be placed in individual beakers so that the splint allows the filter paper to hang down into the beaker, without touching the bottom.  

Water should be then poured into the beaker so that the bottom of the paper is in the water, but not above the pen dot. 

Students should wait until the water has been absorbed to the top of the filter paper and then take them out of their beakers. They should then compare the chromatograms for the mystery pen dot to the other three to determine which pen was used in secret. 

Differentiated tasks (Support/Core/Challenge)

Support:

• Provide visual aids and step-by-step instructions for the activity to support the students’ understanding of the concept of chromatography.
• Offer additional support and guidance during the experiment, helping students to complete the activity and interpret their results.
• Use simpler and more straightforward examples to explain chromatography, such as separating the colours in a fruit drink or candy.

Core: 

• Encourage students to identify patterns in their results and make predictions based on their observations.
• Provide opportunities for students to work in small groups, allowing them to collaborate and compare results.
• Challenge students to think critically about the experiment and its applications by asking questions such as: "Why do you think the colours are separated in this way?" "What are the potential real-world applications of chromatography?"

Challenge: 

• Encourage students to explore chromatography further by using different solvents or trying different types of filter paper.
• Provide opportunities for students to design their own experiments and compare their results with those of their peers.
• Challenge students to analyse their results and draw conclusions about the underlying scientific principles behind chromatography.
• Encourage students to research and present on real-world applications of chromatography, such as its use in the food and drug industries.