Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Chromatography is a physical process used to separate mixtures of soluble substances, such as dyes, inks, and food colorings.
The Stationary Phase is the material that does not move (usually the chromatography paper).
The Mobile Phase is the solvent (such as water or ethanol) that moves through the stationary phase, carrying the components of the mixture.
Separation occurs because different substances have different solubilities in the mobile phase and different affinities for the stationary phase.
A Pure Substance will produce only one spot on the chromatogram, while a Mixture will separate into two or more spots.
The Baseline (starting line) must be drawn in pencil because pencil lead (graphite) is insoluble and will not dissolve in the solvent and interfere with the results.
The solvent level must be below the baseline so that the samples do not dissolve directly into the solvent reservoir.
Locating Agents (e.g., Ninhydrin) are used to visualize colorless substances like amino acids or sugars by reacting with them to produce a colored spot.
The Retention Factor () value is a ratio used to identify substances. For a specific solvent and temperature, the value for a substance is constant.
📐Formulae
💡Examples
Problem 1:
In a paper chromatography experiment, the baseline was drawn from the bottom of the paper. After the experiment, a red dye spot was found to have moved from the baseline, while the solvent front moved from the baseline. Calculate the value for the red dye.
Solution:
Explanation:
The value is calculated by dividing the distance moved by the solute (red dye) by the distance moved by the solvent. Both distances are measured from the starting baseline. Since it is a ratio of the same units, has no units.
Problem 2:
A student tests a sample of black ink. The resulting chromatogram shows three distinct spots at different heights. What can be concluded about the black ink?
Solution:
The black ink is a mixture of at least three different colored substances.
Explanation:
Because the chromatography process resulted in more than one spot, the original substance must be a mixture. Each spot represents a different component that has a different solubility in the mobile phase.