Use Rf values to compare and identify substances.

Purity, formulations and chromatography treats Use Rf values to compare and identify substances as a separate Chemical analysis skill. The approved objective is: Use Rf values to compare and identify substances. The key evidence is spot and solvent-front distances, and the result to look for is Rf or separation evidence. This makes it different from nearby objectives because the answer must stay anchored to Use Rf values to compare and identify substances, not another Chemical analysis test. Useful curriculum keywords include Rf value. Keep the method, observation, and conclusion separate so the answer does not confuse gas tests, flame tests, cation tests, anion tests, chromatography, pure substances, or formulations. A strong exam response states the test or measurement, describes what is seen, and then links that evidence directly to Chromatography.