Chemical Analysis and Laboratory Skills
Core concepts
Analytical chemistry combines qualitative identification with quantitative measurement. Candidates must know flame tests (e.g. sodium yellow, potassium lilac, copper blue-green), precipitation tests (chloride with silver nitrate, sulfate with barium chloride), and gas tests (carbon dioxide turns limewater milky; hydrogen gives a squeaky pop).
Instrumental techniques include flame photometry, colorimetry, titration, and chromatography. Chromatography separates by differential affinity; Rf values are calculated as distance travelled by solute divided by distance travelled by solvent front.
Laboratory skills include safe handling, accurate measurement, correct use of burettes and pipettes, and recording results with appropriate precision and significant figures. Uncertainty and error analysis are examinable.
Traps to watch
- Using tap water rather than distilled water in qualitative tests.
- Forgetting to acidify with nitric acid before testing for halides (to remove carbonate interference).
- Recording readings with too many or too few significant figures.
- Confusing random and systematic errors.
- Assuming Rf values are independent of solvent and conditions.
Worked example
A spot travels 3.0 cm while the solvent front travels 6.0 cm: Rf = 3.0/6.0 = 0.50. Rule of thumb: measure both distances from the same baseline, and Rf must lie between 0 and 1.