Paper Chromatography Full Experiment Including Calculating Rf Values Science4Breakfast GCSE Science

Summary

In this video, the process of chromatography is demonstrated to separate an unknown mixture of colored dyes. Using chromatography paper, a pencil line is drawn, and dots of known and unknown inks are placed on it. The paper is then immersed in a solvent, allowing the dyes to travel up the paper, separating based on their solubility. The distances traveled by the solvent and the dyes are measured, and Rf values (retention factors) are calculated to identify the components of the unknown mixture. This experiment illustrates the principles of chromatography and how it can be used for analysis.

Takeaways

• 😀 The chromatography experiment is designed to separate components of an unknown mixture of colorful dyes.
• 😀 Chromatography paper (filter paper) is essential for the separation process and should be marked with a pencil, not ink, to prevent running.
• 😀 A pencil line should be drawn about 2 cm above the bottom of the chromatography paper to avoid interference with the solvent.
• 😀 Capillary tubes are used to place small dots of known ink colors (yellow, black, red) and the unknown mixture on the paper.
• 😀 The solvent, sodium hydrogen carbonate (or water), is poured into a beaker, and the chromatography paper is suspended in it with a wooden splint and paper clip.
• 😀 It's crucial that the solvent level does not touch or surpass the pencil line on the chromatography paper.
• 😀 As the solvent moves up the paper, the ink spots dissolve into it and are carried upwards, separating into different components.
• 😀 When the solvent approaches the top of the paper, the chromatography paper is removed and allowed to dry.
• 😀 RF values are calculated by dividing the distance traveled by the solute (dye spots) by the distance traveled by the solvent.
• 😀 An RF value helps identify different components in the unknown mixture based on their relative movement in the solvent.
• 😀 The RF value formula is: RF = distance traveled by the solute / distance traveled by the solvent, and RF values have no units.

Q & A

What is the purpose of chromatography in this experiment?

Chromatography is used to separate a mixture of colorful dyes into individual components based on their solubility and interaction with a solvent.

Why is it important to use pencil instead of ink for drawing the line on the chromatography paper?

Pencil is used because it is insoluble, meaning it won't dissolve and travel up the paper with the solvent. Ink, however, could dissolve and interfere with the experiment.

What is the role of the capillary tubes in the chromatography process?

Capillary tubes are used to place small dots of ink onto the chromatography paper. These dots will be separated during the experiment.

Why should the solvent level be below the pencil line when setting up the chromatography?

The solvent must not touch or be above the pencil line to ensure that it only carries the dye spots upward, allowing the separation to occur correctly.

What are the 'stationary phase' and 'mobile phase' in chromatography?

In chromatography, the 'stationary phase' refers to the paper (which doesn't move), while the 'mobile phase' is the solvent that moves up the paper, carrying the dyes with it.

What is the significance of the 'RF' value in chromatography?

The RF value is a ratio that represents how far a solute has traveled relative to the solvent front. It helps identify the compounds in the mixture.

How is the distance traveled by the solute measured?

The distance traveled by the solute is measured from the pencil line (where the dye was applied) to the center of the spot once it has separated.

Why is it important to measure the distance from the middle of the dye spot?

Measuring from the middle ensures accuracy, as the spot may not be perfectly round or even, and this gives a more representative distance.

What is the role of the solvent in this experiment?

The solvent dissolves the dyes, allowing them to travel up the chromatography paper. The solvent's properties affect how the dyes separate.

What should you do if the solvent level touches or exceeds the pencil line?

If the solvent level touches or exceeds the pencil line, you must restart the experiment, as this will cause the pencil line (and potentially the dyes) to move, leading to inaccurate results.