CHEM - Paper Chromatography
Chemistry, separation techniques, paper chromatography - IGCSE | IBDP | DSE | GCE | AP Chemistry
Frequently asked in IGCSE Chemistry are questions on paper chromatography 😄
Paper chromatography is used to separate mixtures based on different solubility in a solvent.
How Paper Chromatography Works:
Calculating Retention Factor (Rf) Value:
Rf = (distance traveled by substance) / (distance traveled by solvent) = a / b
Let's now take a look at some questions from IGCSE Chemistry exams!!
Illegal drugs are sometimes used to affect the performance of racehorses. These drugs can be detected in horse urine using chromatography.
• A concentrated sample of urine from each horse is spotted onto the start line of a sheet of chromatography paper
• Known illegal drugs are also spotted onto the same paper
• Ethanol is used as the solvent
The chromatogram shows urine samples, A, B, C and D, and the two illegal drugs lasix and bute.
Explain which urine sample contains an illegal drug.
Sample C is composed of two substances. One of the substances traveled the same distance as bute, which means sample C contains bute.
A student investigates some food colourings, each of which is made up of one or more dyes. She produces a chromatogram using the safe colourings red (SR), blue (SB) and green (SG) and food colourings red (FR), blue (FB) and green (FG). The diagram shows her chromatogram.
Explain which food colourings are defintely safe to use.
A student investigates the pigments found in some vegetables and fruit. She obtains some coloured vegetable and fruit extracts from carrots, tomatoes and sweet potatoes. She places a spot of each extract on chromatography paper, along with spots of the three pigments beta-carotene, chlorophyll and lycopene. The diagram shows the chromatogram at the end of the experiment.
Key to vegetable and fruit extracts and pigments
V1 = carrots, , V2 = tomatoes, V3 = sweet potatoes, P1 = beta-carotene, P2 = chlorophyll, P3 = lycopene
(a) Suggest a reason why there is a spot on the starting line in the chromatogram for sweet potatoes.
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