Specification references covered: C2.7(e), C2.9–C2.11 (paper chromatography; mobile and stationary phases; Rf values; interpreting chromatograms; ink investigation)

Chromatography generates more calculation marks than any other CC2 topic, and the Rf question appears in most Edexcel papers. The Topic Mastery Sheet explains the mobile/stationary phase terminology, gives a complete 7-step practical method, explains why substances stay on the baseline (insoluble), provides the exact mark scheme wording for the “same ink?” deduction question, and works through Rf calculation with the requirement for 2 decimal places. The interpretation section covers pure vs impure identification and the full reasoning for comparing ink patterns across all spots.

The Student Exam Practice Sheet (20 marks) mirrors the official exam structure exactly - including the method description, why ink M stayed on the baseline, counting dyes in ink X, the same-ink deduction, Rf calculation, phase names, pencil baseline reasoning, and Higher Tier multi-substance identification questions.

The Teacher Answer Key includes all mark scheme wording verbatim, the 2-decimal-place requirement flagged in red, and the full reasoning for the same-ink deduction question.

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