The complete lecture — separation and spectroscopy come alive in the live panel as you read. Scroll down; the animation keeps pace as the inks climb the paper and white light loses its colours.
Components held strongly by the stationary phase move slowly; those that prefer the mobile phase move fast — so the mixture spreads out. Separation is by adsorption (sticking to a surface) or partition (dissolving between two liquids).
Spot the mixture on a pencil base line, dip the paper in solvent below the spot, and let the solvent climb. Components separate; mark the solvent front, then measure.
Rf has no units, is between 0 and 1, and is constant for a compound — so it identifies it.
TLC uses a silica/alumina layer on a plate — faster and sharper than paper, by adsorption. In column chromatography the mixture is loaded on a packed column; weakly bound components elute first, strongly bound ones later, and each is collected separately.
Use a separating funnel; run off the lower layer. Several small extractions remove more solute than one large one.
Spectroscopy studies how matter interacts with EM radiation. In absorption, electrons jump up and remove certain wavelengths (dark gaps). In emission, they fall back and give bright lines. Each element has its own fingerprint.
| Ion | Flame colour |
|---|---|
| Na⁺ | golden yellow |
| K⁺ | lilac |
| Cu²⁺ | blue-green |
UV-visible reads electronic transitions (and concentration); IR reads bond vibrations (functional groups). A spectrometer = source → monochromator → sample → detector → recorder.