Paper chromatography is a technique used to separate mixtures of substances based on their different affinities for a stationary phase (the paper) and a mobile phase (the solvent). It works because different components of a mixture travel at different speeds across the paper.

Apparatus:

• A strip of chromatography paper (usually cellulose-based).
• A suitable solvent (e.g., water, ethanol, or a mixture of solvents).
• A container (e.g., a test tube or beaker) to hold the solvent.
• A pencil for drawing a line on the paper.
• A capillary tube or dropper for applying the sample.
• A clip or tape to hold the paper in the container.

Procedure:

1. Draw a light pencil line about 1-2 cm from the bottom of the chromatography paper. This is where the sample will be applied.
2. Dissolve the coloured mixture in a suitable solvent.
3. Using a capillary tube, carefully apply a small spot of the coloured solution onto the pencil line. Allow the solvent to evaporate completely.
4. Place the chromatography paper in the container, ensuring that the bottom edge of the paper is just above the solvent level. The solvent level should not touch the sample spot.
5. Cover the container with a lid or paper to prevent evaporation of the solvent.
6. Allow the solvent to travel up the paper by capillary action. As the solvent moves, it carries the different components of the mixture with it.
7. As the solvent reaches a certain height, remove the paper from the container and allow it to dry.
8. The separated components of the mixture will appear as distinct spots on the paper. The distance each component travels depends on its solubility in the solvent and its affinity for the paper. Components with higher solubility in the solvent will travel further.

The choice of solvent is crucial. It must be able to dissolve the components of the mixture but not the stationary phase (paper). A suitable solvent is one that allows for a good separation of the components.

Answer:

Answer: Sample X is impure.

Explanation: A pure substance will only consist of one component. Therefore, a pure substance will produce a single spot on the chromatogram. In this case, Sample X produces a single spot with an Rf value of 0.85. However, Sample Y produces a single spot with an Rf value of 0.92. This indicates that Sample X contains multiple components, and therefore is impure. If Sample X were pure, it would have produced only one spot.

Paper chromatography is a separation technique used to separate mixtures based on differences in the partition coefficient of the components between a mobile phase (the solvent) and a stationary phase (the paper). The principle behind this is that different substances have different affinities for the stationary and mobile phases. Substances with a higher affinity for the mobile phase will travel further up the paper than those with a higher affinity for the stationary phase.

Procedure:

• Preparation: A small spot of the mixture is applied near the bottom of a strip of chromatography paper. The paper is then mounted vertically in a container, ensuring the solvent level is below the spot.
• Solvent Choice: The choice of solvent is crucial. It should be a suitable organic solvent that dissolves all the components of the mixture. The solvent's polarity should be chosen so that it effectively dissolves the components but also has a reasonable affinity for the stationary phase (the paper). A solvent that is too polar will cause all components to travel up the paper very quickly and result in poor separation. A solvent that is too non-polar will not dissolve the components effectively. A test run is often performed to determine the optimal solvent.
• Locating Agent: After the solvent front has reached a suitable height, the paper is removed and allowed to dry. The separated components are then visualized using a locating agent. This is a reagent that reacts with the separated substances to make them visible. For example, if the components are organic, a developing agent like potassium permanganate (KMnO4) or iodine vapor can be used. The components will react with the developing agent, producing coloured spots at their respective locations.

The different components of the mixture will travel at different rates up the paper, resulting in their separation. The distance each component travels is related to its partition coefficient. The Rf value (retention factor) is calculated as the distance travelled by the spot divided by the distance travelled by the solvent front. This provides a characteristic value for each compound, allowing for identification.