Practical: Paper chromatography

Explain the method of paper chromatography

• Draw a pencil baseline near the bottom of a piece of chromatography paper.

• Place a small spot of the mixture (e.g., ink or food coloring) on the baseline using a capillary tube.

• Place the paper into a beaker containing a small amount of solvent, ensuring that the baseline is above the solvent level.

• Cover the beaker to prevent evaporation.

• Allow the solvent to move up the paper, carrying the components of the mixture with it.

• Remove the paper when the solvent has nearly reached the top and allow it to dry.

• Measure the distance traveled by the solvent (solvent front) and each component (Rf value = distance traveled by the component ÷ distance traveled by the solvent).

• Compare the Rf values to known standards to identify the components.

Why is a pencil used to mark the baseline in chromatography?

A pencil is used because it is insoluble in the solvent and does not interfere with the separation of components.

What happens if the solvent level is above the baseline in chromatography?

The sample could dissolve into the solvent, leading to inaccurate results.

What is the purpose of the solvent in paper chromatography?

The solvent carries the components of the mixture along the paper, separating them based on their solubility.

How is the Rf value used to identify substances?

The Rf value is compared to known values for a specific substance to identify the components in the mixture.

What is the role of the stationary phase in paper chromatography?

The stationary phase (chromatography paper) provides a surface for the components to interact with, causing separation.

What can affect the results of paper chromatography?

The choice of solvent, temperature, and quality of the chromatography paper can all affect the results.

How can you ensure accurate results in paper chromatography?

Ensure the solvent is clean, the sample is applied accurately, and the paper is not disturbed during the experiment.

Why do different components of the mixture travel at different speeds in chromatography?

Different components have different solubilities in the solvent and different affinities for the stationary phase.

What is meant by the solvent front in paper chromatography?

The solvent front is the furthest point reached by the solvent in the chromatography paper.

How do you calculate the Rf value?

Rf = Distance traveled by the component ÷ Distance traveled by the solvent.

How do you know if a sample is pure using chromatography?

A pure sample will produce only one spot, while impurities will cause additional spots.

Why is it important to use a fresh solvent in chromatography?

A fresh solvent ensures that there are no contaminants affecting the separation of the components.

How can you use chromatography to separate a mixture of food colorings?

Different food colorings will have different solubilities in the solvent and will travel at different speeds, allowing them to be separated.

What type of substances are typically analyzed using chromatography?

Ink, food colorings, plant extracts, and environmental samples like water or air pollutants.

What is the result if all components of a mixture have the same Rf value?

The components cannot be separated effectively as they travel together in the same direction.