Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Chromatography is a technique used to separate and identify components of a mixture based on their relative solubilities in a mobile phase and their affinity for a stationary phase.
The stationary phase is the phase that does not move (e.g., chromatography paper), while the mobile phase is the solvent (e.g., , ethanol, or propanone) that moves through the stationary phase.
The baseline (starting line) must be drawn in pencil because graphite is insoluble in the solvent and will not interfere with the results, unlike ink which would separate into its own components.
The level of the solvent must be below the baseline to prevent the sample spots from dissolving directly into the solvent in the beaker.
A pure substance will produce only one spot on a chromatogram, whereas a mixture will separate into two or more spots.
Locating agents (e.g., ninhydrin) are chemicals used to make colorless substances, such as amino acids or sugars, visible by reacting with them to form colored spots.
The (retention factor) value is a ratio used to identify substances; it is constant for a specific substance under identical conditions of solvent and temperature.
📐Formulae
💡Examples
Problem 1:
In a chromatography experiment, a sample of a dye moved from the pencil baseline. The solvent front reached a distance of from the same baseline. Calculate the value of the dye.
Solution:
Explanation:
The value is calculated by dividing the distance traveled by the component by the total distance traveled by the solvent front. Both measurements must be taken from the same starting point (the baseline).
Problem 2:
Two substances, and , have values of and respectively in a specific solvent. Which substance is more soluble in the mobile phase?
Solution:
Substance is more soluble.
Explanation:
A higher value indicates that the substance has traveled further up the paper. This means Substance has a higher solubility in the mobile phase (solvent) and a lower affinity for the stationary phase compared to Substance .