ChromatographyEdexcel A-Level Chemistry: Flashcards

What these 14 flashcards ask

What does chromatography separate?
What is the mobile phase?
What is the stationary phase?
Why do components separate in chromatography?
How is an Rf value calculated?
What are the units and range of Rf?
Why is the baseline drawn in pencil?
What is the stationary phase in TLC?
What is retention time?
What is the mobile phase in GC?
What is the mobile phase in HPLC?
When is HPLC used instead of GC?
Why is mass spectrometry linked to GC or HPLC?
Give two uses of GC–MS or HPLC–MS.

Exam questions on Chromatography

A forensic analyst separates the dyes in a sample of black ink using thin-layer chromatography (TLC). The plate is coated with a thin layer of silica gel, and a solvent rises up the plate. When the plate is removed, the solvent front has travelled 8.0 cm from the baseline and the centre of one dye spot is 3.2 cm from the baseline.
Explain why the dyes in the ink separate on the plate.2 marks
A laboratory tests urine samples from athletes for banned drugs using gas chromatography coupled with mass spectrometry (GC–MS). The sample is vaporised and carried through a long column by a gas.
Explain why the gas chromatograph is coupled to a mass spectrometer.2 marks
A student separates a mixture of two amino acids by one-way thin-layer chromatography. After development, the solvent front is 12.5 cm from the baseline. Spot 1 has its centre 4.5 cm from the baseline and spot 2 has its centre 9.0 cm from the baseline. Under identical conditions, a reference sample of leucine has an Rf value of 0.72.
Calculate the Rf value of each spot and deduce which spot is leucine.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).