The Science Behind Solving Crimes
🕵️ The Science Behind Solving Crimes
In 1995, a forger was caught because forensic scientists ran chromatography on ink from a document. The ink produced three spots — the forger had mixed different inks to try to match the original. The genuine signature produced only one spot. Paper chromatography, a technique invented in 1944, uses nothing more than paper and solvent to separate mixtures into their individual components. Today it helps catch criminals, test food dyes, and quality-check medicines.
Chemistry glossary
- What is chromatography?
- A separation technique used to separate mixtures into their individual components based on different affinities for mobile and stationary phases
- What does Rf stand for and what does it measure?
- Rf = Retention factor. It measures how far a substance travels compared to the solvent (distance moved by substance ÷ distance moved by solvent)
Chromatography is a separation technique used to separate mixtures into their individual components and to identify those components.
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🧠 Memory Aid
Rf formula: "Rf = substance over Front"
Rf = distance by Substance ÷ distance by solvent Front
The capital S on top, capital F on bottom — "Substance over Front"
For what moves where: "More Soluble = Sprints further up"
For phases: "Mobile MOVES, Stationary STAYS"
Quick Check: A student runs chromatography on a suspected food dye and gets three spots. What does this tell them?
The food dye is a mixture — it contains at least three different coloured compounds. It is not a pure substance.
Now try it yourself
Quiz · Question 1 of 23
What is the purpose of chromatography?
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This topic in real past papers
Every real exam question we've found on chromatography, with a full worked answer.